AN EVALUATION OF MELANOPSIN FUNCTION AND LIGHT … · Govinda Ojha B. Optom Submitted in fulfilment...
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AN EVALUATION OF MELANOPSIN FUNCTION AND LIGHT EXPOSURE IN DEPRESSIVE DISORDERS Govinda Ojha B. Optom Submitted in fulfilment of the requirements for the degree of Masters of Applied Science Medical Retina Laboratory Institute of Health and Biomedical Innovation School of Biomedical Sciences Queensland University of Technology (QUT) Australia 2017
Transcript of AN EVALUATION OF MELANOPSIN FUNCTION AND LIGHT … · Govinda Ojha B. Optom Submitted in fulfilment...
AN EVALUATION OF MELANOPSIN FUNCTION AND
LIGHT EXPOSURE IN DEPRESSIVE DISORDERS
Govinda Ojha
B. Optom
Submitted in fulfilment of the requirements for the degree of
Masters of Applied Science
Medical Retina Laboratory
Institute of Health and Biomedical Innovation
School of Biomedical Sciences
Queensland University of Technology (QUT)
Australia
2017
i
ABSTRACT
Aberrant light exposure causes depression in animals through a pathway involving the
recently discovered intrinsically photosensitive Retinal Ganglion Cells (ipRGCs). The
photopigment melanopsin expressed in ipRGCs encodes irradiance to signal to the non-
image-forming centres of the brain, including the suprachiasmatic nucleus (SCN) for
circadian photoentrainment and the olivary pretectal nucleus (OPN) to control the pupil light
reflex. Mouse models have further identified ipRGC projections to the brain nuclei that
regulate mood and behaviour. In humans, the post-illumination pupil response (PIPR), a
sustained pupillary constriction after light offset, is used as a direct and non-invasive
biomarker of ipRGC function.
The PIPR amplitude is reduced in humans with seasonal affective disorder (SAD) that
shows a seasonal variation in depressive episodes with a peak manifestation in winter when
the solar light exposure is low, but a recent study including patients with non-seasonal
depressive disorder did not detect ipRGC dysfunction. Moreover, neither study measured the
ambient light exposure levels in patients with depression for comparison to healthy
individuals without depression. The knowledge of the role of light coding cells (ipRGCs) in
major depressive disorder (MDD) is incomplete unless the relationship between ambient light
exposure levels and melanopsin function is evaluated. This study aims to measure the
environmental light exposure levels and their relationship with melanopsin-mediated PIPR in
non-seasonal depression. It is hypothesised that the patients with non-seasonal depression are
exposed to low light levels and this is associated with impaired melanopsin function.
A sample of 22 adults was recruited, including people with non-seasonal depression (n
= 8, median age: 35 years) and healthy age-matched controls (n = 14, median age: 29 years).
The presence of a DSM-IV MDD was assessed using the Mini International Neuropsychiatry
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Interview (MINI 6). The severity of depression symptoms was assessed with the Beck
Depression Inventory (BDI-II). Individuals with recurrent MDD assessed with the MINI and
a positive screen on the Seasonal Pattern Assessment Questionnaire and the Hamilton
Depression Rating Scale-SAD (HDRS-SAD) were excluded as SAD. Both groups had visual
acuity ≥ 6/6, normal colour vision and intraocular pressure (IOP) ≤ 21 mmHg, no corneal and
lenticular opacities and normal retinae and optic discs. The ipRGC-mediated PIPR was
measured using a short duration (1 s) high irradiance (15.5 log quanta.cm-2.s-1) short
wavelength (blue appearing) light stimulus with a custom built Maxwellian view
pupillometer. Light exposure levels, sleep-wake times and sleep efficiency were determined
over 2 weeks with an ambulatory light sensor device (Geneactive).
The mean daily light exposure levels were similar between the groups and there were
no statistically significant differences between the groups for light exposure levels as a
function of clock hours, nor in the total number of minutes of exposure to light levels that are
commonly recommended for depression therapy with bright light (e.g., ≥ 10,000 lux, ≥ 5000
lux and ≥ 2500 lux). There were no statistically significant differences in the mean %
baseline PIPR amplitude between the patients with depression (mean % baseline ± SD, 60.31
± 9.2) and healthy control participants (mean % baseline ± SD, 60.25 ± 6.5).
This study expands previous knowledge in depressive disorder to demonstrate that non-
seasonal depression is independent of an individual’s ambient light exposure level and the
patients with non-seasonal depression can have normally functioning light coding ipRGCs.
While depression is a multi-factorial condition, future studies may focus on determining
whether ipRGC sub-types other than M1 with direct projections to brain mood centres have a
role in the pathophysiology of non-seasonal depression.
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KEY WORDS
Ambient light exposure, intrinsically photosensitive Retinal Ganglion Cells (ipRGCs),
melanopsin, non-seasonal depression, pupil light reflex, post-illumination pupil response.
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TABLE OF CONTENTS
ABSTRACT ................................................................................................................................ i
KEY WORDS .......................................................................................................................... iii
LIST OF FIGURES .................................................................................................................vii
LIST OF ABBREVIATIONS .................................................................................................... x
UNITS ......................................................................................................................................xii
ACKNOWLEDGEMENT ...................................................................................................... xiv
CHAPTER 1: INTRODUCTION .............................................................................................. 1
CHAPTER 2: LITERATURE REVIEW .................................................................................. 6
2.1 MELANOPSIN-EXPRESSING INTRINSICALLY PHOTOSENSITIVE RETINAL
GANGLION CELLS: MORPHOLOGY AND RETINAL DISTRIBUTION .......................... 6
2. 2 INTRINSICALLY PHOTOSENSITIVE RETINAL GANGLION CELL
CONTRIBUTIONS TO THE PUPIL LIGHT REFLEX ......................................................... 12
2.3 PROJECTION OF ipRGCs TO MOOD CENTRES IN THE BRAIN .............................. 21
2. 4 AMBIENT LIGHT AND DEPRESSION ........................................................................ 28
2.5 RETINAL FUNCTION IN DEPRESSIVE DISORDERS ................................................ 33
2.6 EXPERIMENTAL AIMS AND HYPOTHESIS ............................................................... 36
CHAPTER 3: EXPERIMENTAL METHODS ....................................................................... 38
3.1 ETHICS STATEMENT ..................................................................................................... 38
3. 2 PARTICIPANTS .............................................................................................................. 38
3.3 ACTIGRAPHY .................................................................................................................. 42
3.4 PSYCHOLOGICAL ASSESSMENTS FOR DEPRESSION ........................................... 44
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3.4.1 MINI INTERNATIONAL NEUROPSYCHIATRIC INTERVIEW .............................. 44
3.4.2 THE BECK DEPRESSION INVENTORY-II (BDI-II) ................................................. 44
3.4.3 SEASONAL AFFECTIVE DISORDERS ...................................................................... 45
3.4.3.1 THE HAMILTON DEPRESSION RATING SCALE -SEASONAL AFFECTIVE
DISORDER VERSION (HDRS-SAD).................................................................................... 45
3.4.3.2 THE SEASONAL PATTERN ASSESSMENT QUESTIONNAIRE (SPAQ) ........... 46
3.5 PUPILLOMETRY ............................................................................................................. 46
3.5.1 PUPILLOMETER CALIBRATIONS ............................................................................ 49
3.5.2 PUPILLOMETRY DATA ANALYSIS ......................................................................... 52
3.6 CONTRAST SENSITIVITY ............................................................................................. 53
3.7 SAMPLE SIZE CALCULATIONS AND POWER ANALYSIS ..................................... 53
3.8 STATISTICAL ANALYSIS ............................................................................................. 54
CHAPTER 4: RESULTS ......................................................................................................... 55
4.1 PARTICIPANT CHARACTERISTICS ............................................................................ 55
4. 2 THE MELANOPSIN-MEDIATED POST-ILLUMINATION PUPIL RESPONSE
(PIPR) ...................................................................................................................................... 59
4. 3 THE PUPIL LIGHT RESPONSE (PLR) .......................................................................... 63
4. 4 CONTRAST SENSITIVITY (CS) ................................................................................... 65
4. 5 LIGHT EXPOSURE ......................................................................................................... 66
CHAPTER 5: DISCUSSION, CONCLUSIONS AND FUTURE DIRECTIONS ................. 71
5. 1 LIMITATIONS ................................................................................................................. 77
5. 2 CONCLUSION AND FUTURE DIRECTIONS .............................................................. 80
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REFERENCES ........................................................................................................................ 83
APPENDICES ......................................................................................................................... 98
1.0 THE PUPIL LIGHT RESPONSE IN DEPRESSION AND CONTROL GROUPS ......... 99
2.0 THE MINI INTERNATIONAL NEUROPSYCHIATRIC INTERVIEW (MINI_6) ..... 101
3.0 THE HAMILTON DEPRESSION RATING SCALE -SEASONAL AFFECTIVE
DISORDER VERSION (HDRS-SAD).................................................................................. 132
4.0 THE BECK DEPRESSION INVENTORY (BDI-II) ...................................................... 137
5.0 THE BECK ANXIETY INVENTORY ........................................................................... 139
6.0 THE SEASONAL PATTERN ASSESSMENT QUESTIONNAIRE (SPAQ) ............... 140
7.0 THE SEASONALITY ASSESSMENT FORM (SAF) ................................................... 142
8.0 THE SLEEP CHART ...................................................................................................... 143
9.0 DEBRIEFING PROTOCOL ............................................................................................ 144
10.0 ACTIGRAPH SLEEP MACRO .................................................................................... 145
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LIST OF FIGURES
Figure 1: The schematic of retinal layers in a mouse model showing ipRGC sub-types. ....... 10
Figure 2: The spectral sensitivity curves of human photoreceptors. ....................................... 13
Figure 3: The pupillary light reflex pathway in primates. ....................................................... 15
Figure 4: The pupil light response plot of a healthy 29-year-old female with normal ocular
health. ....................................................................................................................................... 16
Figure 5: Projections of ipRGCs to the brain centres in a mouse model. ................................ 24
Figure 6: The neuronal and hormonal connections of the SCN............................................... 27
Figure 7: The schematic representation of current knowledge and hypothetical relationships
among ambient light, ipRGC function and depression. ........................................................... 31
Figure 8: The study protocol. ................................................................................................... 42
Figure 9: The Maxwellian view open-loop pupillometer system ............................................ 47
Figure 10: The pupillometry protocol used in the experiment ................................................ 49
Figure 11: The spectral output of the LEDS used in the pupillometer. ................................... 50
Figure 12: The irradiance output calibration of the red and blue LEDs. ................................. 51
Figure 13: The pupil light reflex traces showing the mean pupil diameter with 95%
confidence limits (CL) in patients with depression (n = 8) and control participants (n = 13). 61
Figure 14: The pupil light reflex traces showing a comparison between two stimuli conditions
in patients with depression (n = 8) and control participants (n = 13). ..................................... 61
Figure 15: The 6-second and the plateau PIPR to short and long wavelength light stimuli in
patients with depression (n = 8) and control participants (n = 13). ......................................... 63
Figure 16: The peak pupil constriction (peak PLR) and the transient PLR amplitudes to short
and long wavelength light stimuli in patients with depression (n = 8) and control participants
(n = 13). .................................................................................................................................... 64
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Figure 17: The time to peak pupil constriction amplitude (time to peak PLR) to short and long
wavelength light stimuli in patients with depression (n = 8) and control participants (n = 13).
.................................................................................................................................................. 65
Figure 18: Contrast sensitivity in patients with depression and control participants. ............. 66
Figure 19: Daily mean (±SD) clock hours (A) and circadian hours (B) light exposure
presented in logarithmic lux scales in patients with depression and healthy participants. ...... 68
Figure 20: Daily duration of exposure to the illuminance levels ≥ 10000 lux, ≥ 5000 lux and ≥
2500 lux in patients with depression and control participants. ................................................ 70
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LIST OF TABLES
Table 1: Study inclusion criteria and assessment procedures .................................................. 40
Table 2: BDI-II scores and depression Severity ...................................................................... 45
Table 3: The characteristics of the patients with non-seasonal depression ............................. 55
Table 4: Depression scores on SAD measures in patients with recurrent depressive episodes
on the MINI.............................................................................................................................. 57
Table 5: The demographic and solar exposure characteristics among the patients with
depression and healthy control participants ............................................................................. 59
Table 6: The mean and 95% CL of the PIPR and PLR metrics (% baseline) with red and blue
stimuli compared between the patients with depression and control participants ................... 62
Table 7: The light exposure and sleep profile compared between the patients with depression
and healthy control participants. .............................................................................................. 67
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LIST OF ABBREVIATIONS
AMD: Age-related Macular Degeneration
BDI: Beck Depression Inventory
BPD: Baseline Pupil Diameter
ERG: Electroretinogram
GSE: Global Solar Exposure
GSS: Global Seasonality Score
HDRS: Hamilton Depression Rating Scale
HC: Hippocampus
HPA: Hypothalamic-Pituitary-Adrenal
IGL: Intergeniculate Leaflet
IpRGC: Intrinsically photosensitive Retinal Ganglion Cell
IPL: Inner Plexiform Layer
LC: Locus Coeruleus
LGNd: Dorsal Lateral Geniculate Nucleus
LH: Lateral Hypothalamus
LHb: Lateral Habenula
MA: Medial Amygdala
MDD: Major Depressive Disorder
MINI: Mini International Neuropsychiatric Interview
OPN: Olivary Pretectal Nucleus
PLR: Pupillary Light Response
PIPR: Post-Illumination Pupil Response
SAD: Seasonal Affective Disorder
SCN: Suprachiasmatic Nucleus
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SPAQ: Seasonal Pattern Assessment Questionnaire
SNRI: Serotonin and Norepinephrine Reuptake Inhibitor
SSRI: Selective Serotonin Reuptake Inhibitor
vLGN: Ventral Lateral Geniculate Nucleus
VLPO: Ventrolateral Preoptic Area
VTA: Ventral Tegmental Area
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UNITS
Angle ° Degree
Spatial frequency cpd cycles per degree
Global Solar Exposure KWh.m-2 Kilowatt hour per metre square
Illuminance Lux Lux
Luminance cd.m-2 Candela per metre square
Irradiance watts.cm-2.s-1 watts per square centimetre per second
Log quanta.cm-2.s-1 Log quanta per square centimetre per
second
Time hr Hour
s Second
Wavelength nm Nanometre
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STATEMENT OF ORIGINAL AUTHORSHIP
The work contained in this thesis has not been previously submitted for a degree or diploma
at this or any other higher education institution. To the best of my knowledge and belief, the
thesis contains no material previously published or written by another person except where
due reference is made.
Student Signature: Date: June 2017
QUT Verified Signature
xiv
ACKNOWLEDGEMENT
I would like to express my sincerest gratitude to my supervisors at Queensland
University of Technology (QUT) Dr Beatrix Feigl, Associate Professor Andrew J Zele and
Professor Leanne Hides for providing me an opportunity to conduct my research study in the
Medical Retina and Visual Science laboratories. I am indebted to the continuous guidance
and support they have extended during my Master’s by Research study. I am thankful for the
knowledge they have passed on to me in order to steer me in the right direction whilst
consistently motivating to improve this thesis. Their doors were always open to me whenever
I had a trouble or a question during the course of my research.
I am thankful to Mr Stoyan Stoyanov for teaching me to use the mental health
instrument (MINI 6) for screening my participants. I am highly indebted to my colleague
Prakash Adhikari as he had always been a helping hand in every step of my research work. I
am grateful to the private practice (Psychology Consultants) and the QUT Psychology Clinic
for assistance with patient recruitment.
I must express my profound gratitude to my colleagues Daniel S Joyce, Michelle L.
Maynard and Amithavikram Rugvedi Hathibelagal for their support and encouragement
along my candidature. My deepest acknowledgement goes to my Nepalese friends Dr. Bharat
Raj Poudel, Dr. Apil Gurung and Dipesh Bhattarai, who have made my stay at QUT a fun
one.
I am indebted to all my participants for the time they have spared for my research.
Finally, I would like to thank my wife Reeti for her selfless support and allowing me to stay
away from home for study until late for the last 2 years.
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CHAPTER 1: INTRODUCTION
Depressive disorders are common mental health disorders, occurring in 2 to 17% of the
population, or more than 350 million people worldwide (Choe, Emslie, & Mayes, 2012;
Ferrari, Somerville, Baxter, Norman, Patten, Vos, & Whiteford, 2013; Luppa, Sikorski, Luck,
Ehreke, Konnopka, Wiese, Weyerer, König, & Riedel-Heller, 2012; World Health
Organization, 2008). Depressive disorders are more common in females than in males with
twice the number of females suffering from depression than males (Girgus & Yang, 2015).
Differences in biological response to stress, exposure to stressful life events and social equity
have been thought as few of the several factors leading to the higher proportion of females
with depression (Girgus et al., 2015). Given the increasing global prevalence of depressive
disorders, it is imperative to understand the pathophysiology of depression to inform the
development of new treatments.
Several studies have linked the role of the recently discovered inner retinal melanopsin-
expressing intrinsically photosensitive Retinal Ganglion Cells (ipRGCs) to the regulation of
effect of light on mood and cognitive functions in humans (Laurenzo, Kardon, Ledolter,
Poolman, Schumacher, Potash, Full, Rice, Ketcham, Starkey, & Fiedorowicz, 2016;
Roecklein, Wong, Ernecoff, Miller, Donofry, Kamarck, Wood-Vasey, & Franzen, 2013) and
animals (Legates, Altimus, Wang, Lee, Yang, Zhao, Kirkwood, Weber, & Hattar, 2012).
Aberrant light exposure can cause depressive behaviour in rodents with intact ipRGCs, but
not in those lacking ipRGCs, implicating the role of ipRGCs in regulating the effect of light
on mood (Legates et al., 2012). The regulation of mood in the animal models is thought to be
mediated through ipRGC projections to the brain mood centres (Fernandez, Chang, Hattar, &
Chen, 2016; Gooley, Lu, Fischer, & Saper, 2003; Hattar, Kumar, Park, Tong, Tung, Yau, &
Berson, 2006). In addition, ipRGCs encode irradiance with major inputs to the non-image-
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forming centres of the brain, including the suprachiasmatic nucleus (SCN) to adjust the
central circadian clock to the ~ 24 hours light-dark cycle (Berson, Dunn, & Takao, 2002;
Czeisler, Shanahan, Klerman, Martens, Brotman, Emens, Klein, & Rizzo, 1995a; Fernandez
et al., 2016; Gooley et al., 2003; Warner, Jethwa, Wyse, I'Anson, Brameld, & Ebling, 2010)
and to the olivary pretectal nucleus (OPN) to regulate the pupillary light response (PLR) and
the post-illumination pupil response (PIPR) (Baver, Pickard, Sollars, & Pickard, 2008; Ecker,
Dumitrescu, Wong, Alam, Chen, LeGates, Renna, Prusky, Berson, & Hattar, 2010; Gamlin,
McDougal, Pokorny, Smith, Yau, & Dacey, 2007; Gooley et al., 2003; Hattar et al., 2006;
Hattar, Liao, Takao, Berson, & Yau, 2002; Markwell, Feigl, & Zele, 2010).
The PLR is the pupil constriction in response to light and is contributed by both inner
retinal ipRGCs and outer retinal rods and cones (Adhikari, Zele, & Feigl, 2015b;
Barrionuevo, Nicandro, McAnany, Zele, Gamlin, & Cao, 2014; Joyce, Feigl, Cao, & Zele,
2015; McDougal & Gamlin, 2010) whereas the PIPR, which is a sustained pupil constriction
after light offset (Adhikari et al., 2015b; Gamlin et al., 2007; Hansen, Sander, Kessel,
Broendsted, Kawasaki, Herbst, LundAndersen, Medicinska, & Oftalmiatrik, 2012; Kankipati,
2009; Kankipati, Girkin, & Gamlin, 2010; Markwell et al., 2010; McDougal et al., 2010;
Park, Moura, Raza, Rhee, Kardon, & Hood, 2011; Young & Kimura, 2008), is predominantly
driven by ipRGCs (Adhikari, Feigl, & Zele, 2016a; Gamlin et al., 2007). The measurement of
the PIPR allows for the direct and in vivo assessment of ipRGC function in humans (Adhikari
et al., 2015b; Feigl & Zele, 2014; Gamlin et al., 2007; Kankipati et al., 2010; Markwell et al.,
2010; McDougal et al., 2010; Young et al., 2008). Collectively, the PIPR has been assessed
as a direct and non-invasive biomarker of ipRGC function in human eyes with and without
retinal disease (Adhikari, Zele, Thomas, & Feigl, 2016b; Feigl, Mattes, Thomas, & Zele,
2011; Feigl et al., 2014; Feigl, Zele, Fader, Howes, Hughes, Jones, & Jones, 2012; Kankipati
et al., 2010; Kankipati, Girkin, & Gamlin, 2011; Kelbsch, Maeda, Strasser, Blumenstock,
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Wilhelm, Wilhelm, & Peters, 2016; Markwell et al., 2010; Maynard, Zele, & Feigl, 2015) and
therefore can also be used to measure the input of ipRGC projections to the brain mood
centres to evaluate the melanopsin function in depressive disorders (Laurenzo et al., 2016;
Roecklein et al., 2013).
IpRGCs have highest sensitivity to short wavelength (bluish) light (max = 482 nm)
(Adhikari et al., 2015b; Feigl et al., 2011; Feigl et al., 2014; Gamlin et al., 2007; Markwell et
al., 2010; McDougal et al., 2010; Young et al., 2008), and blue light with high melanopsin
excitation has been shown to have an antidepressant effect in humans with major depressive
disorders (MDD), including seasonal affective disorder (SAD) (Glickman, Byrne, Pineda,
Hauck, & Brainard, 2006; Meesters, Dekker, Schlangen, Bos, & Ruiter, 2011) and non-
seasonal depression (Lieverse, Van Someren, Nielen, Uitdehaag, Smit, & Hoogendijk, 2011;
Royer, Ballentine, Eslinger, Houser, Mistrick, Behr, & Rakos, 2012). SAD is a type of
depression that shows a peak manifestation of depressive symptoms in winter when the solar
light exposure is low (Eastwood & Peter, 1988). The prevalance of SAD ranges from 0% to
9.7% worldwide depending on the latitude (Magnusson, 2000). Non-seasonal depression does
not show seasonal variation of depressive symptoms and the worldwide prevalence of non-
seasonal depression is higher than SAD (7-17%) (Luppa et al., 2012). The mechanism by
which ocular light exposure alleviates the depressive symptoms in patients with MDD is not
understood unless the relationship between environmental light exposure and ocular
photoreception function of the main light coding cells is known. While the patients with
SAD are exposed to a similar ambient light exposure level as healthy individuals, irrespective
of the season (Graw, Recker, Sand, Kräuchi, & Wirz-Justice, 1999; Guillemette, Hébert,
Paquet, & Dumont, 1998; Oren, Moul, Schwartz, Brown, Yamada, & Rosenthal, 1994),
studies have linked the role of retinal photoreception by rods and cones to justify the positive
effect of light in SAD (Lavoie, Lam, Bouchard, Sasseville, Charron, Gagné, Tremblay,
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Filteau, & Hébert, 2009; Ozaki, Rosenthal, Moul, Schwartz, & Oren, 1993; Szabó, Antal,
Tokaji, Kálmán, Kéri, Benedek, & Janka, 2004). The cone-pathway mediated visual contrast
sensitivity is reported to be similar or higher in SAD patients than in healthy individuals
(Szabó et al., 2004; Wesner & Tan, 2006) whereas studies on contrast sensitivity in non-
seasonal depression are inconsistent showing an increased (Wesner et al., 2006) or decreased
(Bubl, Tebartz Van Elst, Gondan, Ebert, & Greenlee, 2009; Fam, Rush, Haaland, Barbier, &
Luu, 2013) sensitivity among the patients with depression. Nevertheless, electrophysiology
studies consistently demonstrate a reduction in neuroretinal function in both SAD (Hébert,
Beattie, Tam, Yatham, & Lam, 2004; Hébert, Dumont, & Lachapelle, 2002; Lam, Beattie,
Buchanan, & Mador, 1992; Lavoie et al., 2009) and non-seasonal depression (Bubl, Kern,
Ebert, Bach, & van Elst, 2010; Bubl, Kern, Ebert, Riedel, van Elst, & Bach, 2015) indicating
that there are changes in retinal function involving the outer retinal rod and/or cone pathways.
Interestingly, the inner retinal ipRGC mediated PIPR amplitude is reduced in SAD in winter
when depressive episodes of the patients are at peak (Roecklein et al., 2013). A recent study,
however, observed no difference in the PIPR in patients with MDD including SAD
compared to healthy individuals (Laurenzo et al., 2016). The discrepancy in the PIPR results
among the patients with depression between the two studies may have occurred due to the
PIPR measurements in the (Laurenzo et al., 2016) study being conducted during both the
winter and summer months when depression and remission occur respectively, possibly
altering the melanopsin function with season (Münch, Kourti, Brouzas, & Kawasaki, 2016).
In particular, Laurenzo et al. (2016) demonstrated that the PLR to low intensity short and
long wavelength light stimuli, which preferentially reflects the outer retinal photoreception
when measured using the transient pupil response (Adhikari et al., 2015b; Feigl et al., 2012;
Kardon, Anderson, Damarjian, Grace, Stone, & Kawasaki, 2009), is reduced in patients with
MDD. Although, the PIPR and transient PLR in response to a high-intensity and short
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wavelength light stimulus have a significant positive relationship with light exposure in MDD
(Laurenzo et al., 2016), no study has compared the ambient light exposure through 24 hours
in a day in individuals with and without non-seasonal MDD. Treatment of depression with
ocular light exposure is commonly provided through light levels ranging from 2500 to 10,000
lux (Even, Schröder, Friedman, & Rouillon, 2008; Gallin, Terman, Reme, Rafferty, Terman,
& Burde, 1995; Glickman et al., 2006; Haffmans, Schouten, & den Hoed, 2008; Kräuchi,
Wirz-Justice, & Graw, 1990; Meesters et al., 2011; Naus, Burger, Malkoc, Molendijk, &
Haffmans, 2013; Szabó et al., 2004; Winkler, Pjrek, Praschak-Rieder, Willeit, Pezawas,
Konstantinidis, Stastny, & Kasper, 2005; Wirz-Justice, Graw, Roosli, Glauser, &
Fleischhauer, 1999), but no study has evaluated the habitual exposure durations to these
ranges of illuminance of ambient light in patients with non seasonal depressive disorders.
Hence, the relationship between light exposure and retinal photoreception that mediates light
therapy in non-seasonal depression is not known.
This study aims to evaluate the environmental light exposure levels and their
relationship to the inner and outer retinal photoreceptor function using the pupil light
response and contrast sensitivity in individuals with and without non-seasonal depression.
Using a Maxwellian view pupillometer and optimised stimulus paradigms that are robust in
detecting subtle melanopsin defects (Adhikari et al., 2015b; Adhikari et al., 2016b), the
present study tests the hypothesis that individuals with non-seasonal depression have reduced
PIPR and PLR amplitudes that are associated with lower daily ambient light exposure levels
compared to the healthy individuals. The study further examines the hypothesis that patients
with non-seasonal depression have reduced visual contrast sensitivity than healthy people.
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CHAPTER 2: LITERATURE REVIEW
This chapter includes review of the current literature on melanopsin-expressing
intrinsically photosensitive Retinal Ganglion Cells (ipRGCs) and their role in mediating the
pupil light reflex and mood through their projections to different brain areas. With ipRGCs,
rods and cones being the main “light sensors” of the visual system, the role of light exposure
in the etiology of depressive disorders and their relationship with rod, cone and ipRGC
function are reviewed. The review leads to the experimental aims and hypothesis of the
thesis.
2.1 MELANOPSIN-EXPRESSING INTRINSICALLY
PHOTOSENSITIVE RETINAL GANGLION CELLS: MORPHOLOGY
AND RETINAL DISTRIBUTION
Light-sensitive melanopsin was first discovered in the skin of the frog (Xenopus laevis)
(Provencio, Jiang, De Grip, Hayes, & Rollag, 1998; Rollag, 1996; Seldenrijk, Hup, de Graan,
& van de Veerdonk, 1979). However, the photic entrainment in mammalian vertebrates is
not extraocular (Nelson & Zucker, 1981) suggesting ocular photopigments being involved in
non-image-forming functions in mammals. Only four distinct photopigments were thought to
exist in the mammalian retina; one rod and three cone opsins, although there was an early
evidence of the existence of another photoreceptor class that regulated iris movement in blind
mice (Keeler, 1927). In addition, a reduction in the release of melatonin in response to light
in blind patients with rod and cone degeneration further suggested the presence of an
unknown photopigment (Czeisler et al., 1995a; Lockley, Skene, Arendt, Tabandeh, Bird, &
Defrance, 1997). A fifth class of photopigment, melanopsin, expressed in the ganglion cells
in the mammalian retina, was subsequently discovered and described using nocturnal mouse
models (Berson et al., 2002; Hattar et al., 2002; Provencio, Rollag, & Castrucci, 2002).
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Melanopsin-expressing retinal ganglion cells were subsequently identified in non-human
primates and in human’s retinae (Dacey, Liao, Peterson, Robinson, Smith, Pokorny, Yau, &
Gamlin, 2005) and these cells constitute 0.2% (~3,000) in the primates and 0.4% (~4,400)
human retinae (Liao, Ren, Peterson, Marshak, Yau, Gamlin, & Dacey, 2016).
IpRGCs are defined as a group of cells constituting uniform morphology and
physiology (Berson et al., 2002; Hattar et al., 2002). They can be histologically differentiated
in the retina from the midget and parasol ganglion cells of the parvocellular and
magnocellular pathway, based on their large cell bodies (diameter 19±3 µm to 23±3 µm in
human) and dendritic trees (diameter 646±151 µm to 690±148 um in human) which arborise
in the inner plexiform layer (Dacey et al., 2005; Liao et al., 2016). The dendritic field
diameter in both human and macaque retinae increases from the fovea to the periphery with
the dendritic field diameter in both human and macaque retina increasing from ~250 µm at
the fovea to ~1200 µm at ~16 mm of retinal eccentricity with dendrites at the fovea forming a
plexus surrounding the foveal pit (Dacey et al., 2005; Jusuf, Lee, Hannibal, & Grünert, 2007;
Liao et al., 2016). The peak ipRGC density decreases from the fovea (30-35 cells/mm2) to the
peripheral retina (8-10 cells/mm2) through ~16 mm of retinal eccentricity in the human retina
(Liao et al., 2016). However, in the mouse retina, the highest ipRGC density was seen in the
superior temporal quadrant (Galindo-Romero, Jiménez-López, Garcia-Ayuso, Salinas-
Navarro, Nadal-Nicolás, Agudo-Barriuso, Villegas-Pérez, Avilés-Trigueros, & Vidal-Sanz,
2013; Hattar et al., 2002).
Figure 1 shows the different ipRGC sub-types and their dendritic stratification within
the inner plexiform layer. Together with the two types of ipRGCs, the outer stratifying (M1)
and inner stratifying (M2) that were originally discovered, a third bistratified ipRGC (M3)
was identified in the mouse retina (Schmidt & Kofuji, 2011b; Schmidt, Taniguchi, & Kofuji,
2008; Viney, Balint, Hillier, Siegert, Boldogkoi, Enquist, Meister, Cepko, & Roska, 2007). In
8
humans and macaques, two sub-types of ipRGCs (M1 and M2) have been identified (Liao et
al., 2016). The M1 cells are the most prominent ipRGCs in number and have the largest
dendritic branches, but with the smallest soma size (Berson, Castrucci, & Provencio, 2010;
Provencio et al., 2002). The dendrites of outer stratifying M1 ipRGCs extend to the OFF sub-
laminae of the inner plexiform layer (Berson et al., 2002; Hattar et al., 2006; Hattar et al.,
2002; Liao et al., 2016) and receive OFF input when the signals from amacrine cells have
been blocked (Wong, Dunn, Graham, & Berson, 2007).
The outer stratifying M1 melanopsin cells receive synaptic contact from dopaminergic
axons of the amacrine cells, whereas the inner stratifying M2 melanopsin cells are contacted
by DB6 bipolar cells (Liao et al., 2016; Viney et al., 2007). A small number of M1 ipRGCs
(~ 10%) have been identified in the mouse retina that have axonal collaterals projecting back
to the inner plexiform layer where they provide synaptic input to dopaminergic amacrine
cells that are thought to be involved in the modulation of cone-driven light adaptation (Joo,
Peterson, Dacey, Hattar, & Chen, 2013; Prigge, Yeh, Liou, Lee, You, Liu, McNeill, Chew,
Hattar, Chen, & Zhang, 2016; Viney et al., 2007). The wild-type mice showed an increase in
the b-wave of the light-adapted ERG amplitude while no change in the b-wave amplitude
under similar condition was seen in the mice lacking M1 ipRGCs. The ERG response was
restored by the injection of dopamine receptor agonist (Prigge et al., 2016) indicating a
possible role of M1 ipRGCs in image forming visual functions as retrograde light signaling
from melanopsin to dopaminergic amacrine cells triggers the release of dopamine (Dkhissi-
Benyahya, Coutanson, Knoblauch, Lahouaoui, Leviel, Rey, Bennis, & Cooper, 2013), a
neurotransmitter that has role in the light-adapted visual function (Jackson, Ruan, Aseem,
Abey, Gamble, Stanwood, Palmiter, Iuvone, & McMahon, 2012).
M1 ipRGCs have been further classified into 2 distinct sub-types in mice based on the
expression of Brn3b transcription factor (Chen, Badea, & Hattar, 2011). Brn3b-negative M1
9
ipRGCs project the SCN for circadian photoentrainment and Brn3b-positive ipRGCs project
other brain targets, including the OPN for regulating the pupil light reflex (Chen et al., 2011).
Other ipRGC sub-types arborising in the ON sub-laminae of the inner plexiform layer also
show a Brn3b expression (Chen et al., 2011). Projection to the mood centres by outer
stratifying (M1) ipRGCs, that share similar expression to Brn3b as inner stratifying (M2, M4
and M5) ipRGCs, have not been confirmed in mice and humans. Yet, it is confirmed in mice
that pupillary light response and circadian photoentrainment are brought about by different
M1 ipRGC sub-types indicating the two processes being independent (Chen et al., 2011).
Similar Brn3b based differentiation of ipRGCs and projections of M1 ipRGCs in humans is
not known.
10
Figure 1: The schematic of retinal layers in a mouse model showing ipRGC sub-types.
The outer retina comprises a photoreceptor layer that contains rods and cones that synapse
with bipolar cells in the outer plexiform layer. The inner nuclear layer contains the cell bodies
of bipolar cells that synapse with the dendrites of ipRGCs in the inner plexiform layer. The
ganglion cell layer contains the ipRGCs. 5 sub-types of ipRGCs (M1, M2, M3, M4 and M5)
with their dendritic stratification to the inner plexiform layer are shown (see text for detail).
The expression of melanopsin in M1 ipRGCs is higher than that in other ipRGC sub-
types (Baver et al., 2008; Hattar et al., 2006). M2 cells have larger soma, dendritic length,
dendritic field and more complex dendritic arbors than M1 cells (Liao et al., 2016; Schmidt &
Kofuji, 2009). M2 ipRGCs are 10 times less sensitive to 480 nm light than M1 cells (Schmidt
et al., 2009). M2 cells are extended into the ON sub-laminae of the inner plexiform layer
(Dacey et al., 2005; Liao et al., 2016; Schmidt et al., 2008). M3 ipRGCs have bi-stratified
dendritic arbors encroaching both ON and OFF sub-laminae of the inner plexiform layer
11
(Provencio et al., 2002; Schmidt et al., 2011b; Warren, Allen, Brown, & Robinson, 2003).
M3 ipRGCs are identical to M2 with respect to the size of their soma and dendritic branching
(Schmidt et al., 2011b). An additional two types of ipRGCs named M4 and M5 were
identified in the mouse retina (Ecker et al., 2010), which Berson et al. (2010) described as
large alpha-like retinal ganglion cells (RGCs). M4 and M5 ipRGCs express weak melanopsin
and are less intrinsically photosensitive than M1, M2 and M3 (Ecker et al., 2010; Estevez,
Fogerson, Ilardi, Borghuis, Chan, Weng, Auferkorte, Demb, & Berson, 2012). The dendrites
of M4 and M5 ipRGCs stratify into the ON sub-laminae of the inner plexiform layer (Ecker
et al., 2010; Estevez et al., 2012). M4 ipRGCs have the largest somas, thickest dendrites and
a more radiating dendritic trees and these cells possess larger ON-centre and OFF-surround
receptive fields than other ipRGC sub-types (Ecker et al., 2010; Estevez et al., 2012). These
cells resemble ON alpha-like conventional retinal ganglion cells in mice and exhibit a
sustained and robust response like M2 cells (Estevez et al., 2012) with a higher intrinsic
response threshold (Berson et al., 2010; Estevez et al., 2012). M5 ipRGCs are small with
dense and bushy dendritic processes innervating the inner (ON) sub-laminae of the inner
plexiform layer (Ecker et al., 2010). M4 and M5 ipRGCs are believed to project to the dorsal
lateral geniculate nucleus (LGNd) and superior colliculus (SC) and are thought to contribute
to image forming visual functions (Ecker et al., 2010; Estevez et al., 2012). Recent evidence
suggests that there are more than 5 sub-types of ipRGCs (personal communication with Prof
D Berson, Friedenwald lecture, Annual Meeting of the Association of research in Vision and
Ophthalmology, 2015).
In conclusion, there are at least five ipRGCs sub-types in rodents and as yet, only two
ipRGC sub-types have been identified in humans and non-human primates, the outer
stratifying M1 and inner stratifying M2 ipRGCs. The axonal projection of ipRGCs through
the optic nerve to the brain areas regulating the pupil light reflex (Baver et al., 2008; Ecker et
12
al., 2010; Gooley et al., 2003; Hattar et al., 2006; Hattar et al., 2002), circadian rhythm
(Baver et al., 2008; Berson et al., 2002; Gooley, Lu, Chou, Scammell, & Saper, 2001; Gooley
et al., 2003; Hannibal, Hindersson, Østergaard, Georg, Heegaard, Larsen, & Fahrenkrug,
2004; Hattar et al., 2002) and mood (Davis & Whalen, 2001; Hattar et al., 2006; Hattar et al.,
2002; Matsumoto & Hikosaka, 2007; Schmidt, Chen, & Hattar, 2011a), have been
demonstrated in rodents, and these will be reviewed in the following sections.
2. 2 INTRINSICALLY PHOTOSENSITIVE RETINAL GANGLION
CELL CONTRIBUTIONS TO THE PUPIL LIGHT REFLEX
The Olivary Pretectal Nucleus (OPN) is the brain centre for regulation of the pupil light
response in mammals (Gamlin, Zhang, & Clarke, 1995). The OPN receives 45% of its
innervation from M1 and 55% from M2 ipRGCs (Baver et al., 2008) in mice. M1 ipRGCs
project to the shell of the OPN that controls the pupil light response and M2 ipRGCs
innervate the OPN core, but its function is unknown (Baver et al., 2008; Ecker et al., 2010;
Gooley et al., 2003; Hattar et al., 2006; Hattar et al., 2002). Although the photopigment
density of ipRGCs (~ 3 um-2) is lower than that of rods and cones (~ 25,000 um-2) (Liebman,
Parker, & Dratz, 1987), ipRGCs exhibit a larger single photon intrinsic response (Do, Kang,
Xue, Zhong, Liao, Bergles, & Yau, 2009). IpRGCs also receive extrinsic synaptic impulses
from rods and cones to serve non-image-forming functions (Belenky, Smeraski, Provencio,
Sollars, & Pickard, 2003; Dacey et al., 2005; Jusuf et al., 2007; Schmidt & Kofuji, 2010;
Wong et al., 2007). However, the extrinsic response has a higher temporal resolution
(Barrionuevo et al., 2014; Joyce et al., 2015) than the intrinsic response which is slower and
more sustained (Barrionuevo et al., 2014; Gamlin et al., 2007; Joyce et al., 2015; Kardon et
al., 2009; Markwell et al., 2010). The peak spectral sensitivity of the melanopsin
photopigment (max = 482 nm) lies between those of S-cones (max = 440 nm) and rods
13
(max = 507 nm) (Gamlin et al., 2007; Markwell et al., 2010; McDougal et al., 2010). Figure
2 shows the spectral sensitivities of ipRGCs, rods and L, M, S-cones.
Figure 2: The spectral sensitivity curves of human photoreceptors.
The peak spectral sensitivities of the S-cone (max = 440 nm), ipRGC (max = 482 nm), rod
(max = 507 nm), M-cone (max = 543 nm) and L-cone (max = 566 nm) are shown (from
Feigl & Zele, 2014).
Figure 3 shows a schematic of the pupillary pathway that modulates the pupillary light
reflex in primates. The autonomic pupil response is regulated by the autonomic innervations
to iris muscles, the sphincter and the dilator pupillae (for review, see McDougal & Gamlin,
2015). The sphincter pupillae consist of annular bands of muscle fibres that receive
cholinergic (parasympathetic) innervation to induce pupillary constriction in response to a
light stimulus, whereas the dilator pupillae are radial muscle fibres that receive adrenergic
(sympathetic) innervations at light offset to cause pupillary dilation (McDougal & Gamlin,
2015). The optic nerve serves as an afferent pathway projecting to the OPN which relays to
the Edinger-Westphal nuclei (Gamlin et al., 1995). The preganglionic fibres of the
14
parasympathetic pathway that originate from the Edinger-Westphal nuclei travel along the
oculomotor nerve to synapse with the postganglionic neurons in the ciliary ganglion. The
sympathetic pathway that originates at the ciliospinal centre located at C8-T2 in the spinal
cord travels up to the superior cervical ganglion in the neck where the neurons synapse with
the postganglionic neurons. The postganglionic neurons ascend up the neck through the
ciliary ganglion and enter into the eye via the short or long ciliary nerves or through the optic
canal to innervate the dilator muscle of the iris causing pupillary dilation (McDougal et al.,
2015). The parasympathetic and sympathetic innervations contribute to the steady state
(baseline) pupil diameter, which is influenced by several factors, including the retinal
illuminance, accommodation, emotional state (e.g., fear, stress, depression) and cognitive
functions (Bradley, Miccoli, Escrig, & Lang, 2008; Guinjoan, Bernabó, & Cardinali, 1995;
Steinhauer, Siegle, Condray, & Pless, 2004). Cholinergic agonists like pilocarpine constrict
the pupil while cholinergic antagonists (e.g., atropine, tropicamide) and adrenergic agonists
(e.g., Phenylephrine) cause pupillary dilation (McDougal et al., 2015).
15
Figure 3: The pupillary light reflex pathway in primates.
The optic nerve relays the light signal to the Olivary Pretectal Nucleus to regulate the pupil
light reflex. The Edinger-Westphal nuclei mediate the consensual pupil light reflex as each of
them project nerve fibres to both ipsilateral and contralateral pupils. The oculomotor nerve
serves as an efferent pathway for initiating pupillary constriction in response to a light
stimulus. The parasympathetic nerve fibres (red dashed line) and the sympathetic nerve fibres
(blue dashed line) are shown (see text for detail).
The pupil light reflex (PLR) is the pupillary constriction during light stimulus and both
outer (rods and cones) and inner (ipRGCs) retinal photoreceptors contribute to the PLR
(Adhikari et al., 2015b; Gamlin et al., 2007; Kardon et al., 2009; McDougal et al., 2010; Park
et al., 2011). Figure 4 shows the pupillary light reflex in response to a 1 s short wavelength,
bluish (464nm) pulsed stimulus during light stimulus (PLR) and after light offset (PIPR) with
different metrics that can be derived from the PLR and PIPR.
16
-1 0 0 1 0 2 0 3 0
3 0
4 0
5 0
6 0
7 0
8 0
9 0
1 0 0
T im e ( s )
Pu
pil
Dia
me
ter (
% b
as
eli
ne
)
B a s e l in e P u p i l D ia m e te r
P L R L a te n c y
T r a n s ie n t P L R
P e a k P u p i l
C o n s t r ic t io n
6 - s e c o n d P IP R
P la te a u P IP R
P o s t- i l lu m in a t io n P u p i l R e s p o n s e
( P IP R )
Figure 4: The pupil light response plot of a healthy 29-year-old female with normal
ocular health.
The plot of the pupil light response over time to a 1 s short wavelength, bluish (464 nm) light
stimulus (black rectangle) is shown. The gray line shows the exponential model fitted over
the PIPR trace (blue) in response to a 1 s short wavelength light stimulus. The 6 s PIPR
metric represents the pupillary constriction at 6 s after the light offset (gray vertical line). The
plateau metric is the plateau of the exponential model. The PLR is described by the PLR
latency, transient PLR and peak pupil constriction. The peak constriction amplitude is the
maximum pupil constriction during the light onset. The PLR latency is the time to 1%
constriction during light onset and the transient PLR is the peak change in pupil diameter
between 180 to 500 ms of light onset (see Adhikari et al, (2015b) for an overview of the PLR
and PIPR metrics).
The transient PLR is the initial pupil constriction (peak constriction between 180 to 500
ms) and it measures the outer retinal rod and cone contribution to the PLR (Adhikari et al.,
2016b; Feigl et al., 2012; Kardon et al., 2009; Laurenzo et al., 2016). The longer time to peak
constriction amplitude (1.4 - 1.9 s) in response to a short wavelength light stimulus of
irradiance > 11 log quanta.cm-2sec-1 is indicative of a slower response from the melanopsin
17
(Adhikari et al., 2015b; Joyce et al., 2015). The PLR to a short duration pulsed stimulus (< 10
s) is dominated by rods with a minimal contribution by cones (McDougal et al., 2010). The
PLR to longer duration stimuli (> 10 s) and at low irradiance (< 7 log quantacm-2sec-1) below
the melanopsin threshold (Dacey et al., 2005; Wong, 2012) has contributions from rods only
(Markwell et al., 2010; McDougal et al., 2010). Rod contributions to the PLR at higher
irradiances (> 11 log quanta.cm-2.sec-1) and long duration (> 10 s) stimuli are minimal and
PLR is mainly contributed by ipRGCs (McDougal et al., 2010).
The PLR measured with a sine wave sinusoidal light stimulus evaluates the response of
both inner and outer retinal photoreceptors (Feigl et al., 2014; Maynard et al., 2015). A phasic
amplitude percentage metric can be derived that measures the phasic peak-to-trough
amplitude during the stimulus presentation reflecting the inner and outer retinal interaction
(Feigl et al., 2014; Maynard et al., 2015). The PLR in response to a sinusoidal light stimulus
can be derived as a combined vector sum of the inputs from rod, cone and melanopsin
(Barrionuevo et al., 2014). At low irradiance (< 11.8 log quanta.cm-2.sec-1) the PLR is
contributed by rod and cone reflecting outer retinal contribution (Barrionuevo et al., 2014).
At high irradiance (> 11.8 log quanta.cm-2.sec-1), the PLR is contributed by melanopsin and
cones (Barrionuevo et al., 2014). At an intermediate range of irradiance (11.8 - 12.1 log
quanta.cm-2.sec-1), the PLR in response to a sinusoidal stimulus is contributed by all three
photoreceptors reflecting the interaction between the inner and outer retina (Barrionuevo et
al., 2014). Joyce et al. (2015) demonstrated that phasic peak-trough pupil amplitude is lower
and the time to initial constriction is longer under high melanopsin excitation condition
indicating a typical response derived from the inner retina. At low melanopsin condition, the
phasic peak to trough amplitude is higher and the time to initial constriction is shorter
reflecting outer retinal contribution (Joyce et al., 2015).
18
The PIPR is the sustained pupil constriction after light offset (Figure 4). The PIPR
amplitude measured > 1.7 s of the light offset reflects melanopsin functions, whereas the
early redilation phase of the PIPR < 1.7 s after the light offset has contributions from both,
melanopsin and rhodopsin (Adhikari et al., 2016a). The PIPR amplitude increases with
increasing retinal irradiance to attain half maximal pupil constriction (> 1.5 mm) at 13.5 log
quanta.cm-2.sec-1 and then plateaus to maximum constriction (> 2.9 mm) at a corneal
irradiance of ~ 15 log quanta.cm-2.sec-1 (Adhikari et al., 2015b; Gamlin et al., 2007; Joyce,
Feigl, & Zele, 2012).
Several studies have evaluated the PIPR with a range of stimulus paradigms in healthy
and diseased eyes using different metrics (for review, see Feigl & Zele, 2014). The PIPR has
been measured as percentage plateau amplitude of the baseline pupil diameter (Plateau PIPR)
(Adhikari et al., 2015b; Feigl et al., 2011; Gamlin et al., 2007; Kankipati et al., 2010;
Kankipati et al., 2011; Roecklein et al., 2013), at 6 s after light offset (6 s PIPR) (Adhikari et
al., 2015b; Laurenzo et al., 2016; Maynard et al., 2015; Park et al., 2011) (Figure 4), as the
net PIPR which is the difference in plateau PIPR in response to long and short wavelength
light stimuli (Feigl et al., 2012; Kankipati et al., 2010; Roecklein et al., 2013), and as early
and late area under the curve (early and late AUCs) (Adhikari et al., 2015b; Herbst, Sander,
Lund-Andersen, Broendsted, Kessel, Hansen, & Kawasaki, 2012). Although, the net PIPR is
used to control non-specific factors like fatigue in PIPR, the plateau and 6-second PIPR
metrics have the lowest coefficient of variation and are therefore recommended for clinical
studies (Adhikari et al., 2015b).
While stimuli durations of 1 s (Adhikari et al., 2016a; Adhikari et al., 2016b; Joyce,
Feigl, & Zele, 2016b; Laurenzo et al., 2016; Park & McAnany, 2015; Park et al., 2011), 10 s
(Feigl et al., 2011; Feigl et al., 2012; Kankipati et al., 2010; Kankipati et al., 2011) and 30 s
(Roecklein et al., 2013) are routinely used, the 1 s short duration stimulus is shown to
19
generate a larger PIPR than a long duration 10 s or 30 s pulse possibly because ipRGCs adapt
to a continuous light pulse (Adhikari et al., 2015b; Joyce, Feigl, & Zele, 2016a; Park et al.,
2011; Wong, Dunn, & Berson, 2005). Importantly, the PLR and PIPR amplitudes vary with
stimulus field size exhibiting higher constriction and PIPR amplitudes with a larger field size
(Joyce et al., 2016b; Park et al., 2015) and in the central retina compared to the peripheral
retina (Joyce et al., 2016b). Based on the previous works (Adhikari et al., 2015b; Joyce et al.,
2016b; Park et al., 2011), a short duration (1 s) short wavelength (465 nm) pulsed stimulus
with a high corneal irradiance (15.5 log quanta.cm-2.sec-1) and a large field size (field
diameter 40°) stimulus will be used for determining the melanopsin function in patients with
non-seasonal depressive disorders in this study.
The pupil light response in human is measured with a pupillometer to control the light
input and record the change in pupil diameter, typically under an infra-red illumination
(Loewenfeld & Lowenstein, 1993). A pupil is a mobile aperture that influences the amount of
light irradiance reaching the retina. With a closed-loop condition, the retinal irradiance is
reduced due to shading by the iris and this decreases the pupil constriction amplitude in
response to short (1 s) or long (30 s) duration light stimuli. Iris shading is expected with a
short duration (1 s) light stimulus because of very short pupil constriction latency (200 – 240
ms) (Adhikari et al., 2015b; Bergamin & Kardon, 2003), causing iris movement for
approximately 1/4th -1/5th a second. Hence, a constant retinal irradiance cannot be achieved
under a closed-loop condition without the use of pharmacological pupil dilation (Loewenfeld
et al., 1993). Since, a Newtonian view pupillometer projects a divergent beam under a closed-
loop condition, preclinical changes in the pupil responses may be harder to detect given the
controlled retinal illumination can only be achieved with a pharmacological dilated pupil that
allows for the measurement of the largest consensual pupillary response (Adhikari, Pearson,
Anderson, Zele, & Feigl, 2015a). An open-loop condition allows a complete entry of the light
20
into the eye without iris shading (Loewenfeld et al., 1993) and can be achieved by using a
Maxwellian view system (Loewenfeld et al., 1993) that focuses the light beam on a small
area of the pupil to ensure the complete entry of the light irrespective of the pupil size
(Westheimer, 1966). With a Maxwellian view system, the pupil diameter of the stimulated or
contralateral eye can be recorded without pupil dilation (Adhikari et al., 2015a).
Previous studies in major depressive disorder (MDD) and seasonal affective disorder
(SAD) used Newtonian view pupillometer without pharmacological pupillary dilation
(Laurenzo et al., 2016; Roecklein et al., 2013) and showed discordant results. The initial
study of patients with SAD by Roecklein et al. (2013) measured the PIPR amplitude in
response to a long duration (30 s) short wavelength light stimuli (12.3 log quanta.cm-2.s-1)
and observed a significant reduction in the PIPR amplitude compared to the healthy controls
(Roecklein et al., 2013). In contrast, the second study by Laurenzo et al. (2016) measured the
PIPR in response to a shorter duration (1 s) and a higher irradiance (~ 14.8 log quanta.cm-2.s-
1) short wavelength light stimulus and did not detect a difference in PIPR amplitude in MDD
patients including SAD compared to healthy controls (Laurenzo et al., 2016). Although, there
is no study comparing the sensitivity and specificity between the Maxwellian and Newtonian
optics pupillometers, Maxwellian optics pupillometers have been used to detect subtle
melanopsin defects in glaucoma suspects, early glaucoma and early age-related macular
degeneration (Adhikari et al., 2016b; Maynard et al., 2015). Hence, the differences in PIPR
between the MDD/SAD and healthy group in the previous studies (Laurenzo et al., 2016;
Roecklein et al., 2013) is expected to have increased with Maxwellian view pupillometers.
The difference in the PIPR between the studies may also have occurred due to the seasonal
variation of the PIPR (Münch et al., 2016) in the recent study (Laurenzo et al., 2016) that was
conducted in both winter and summer months as opposed to the previous SAD study
(Roecklein et al., 2013), which was conducted in winter when the depressive episodes of the
21
patients with SAD were at peak. The Laurenzo et al. (2016) study further quantified the peak
constriction amplitude and transient PLR in response to low intensity red and blue light
stimuli (~ 11.9 log quanta.cm-2.s-1) and observed a significant reduction in the peak
constriction and transient PLR amplitudes in MDD (Laurenzo et al., 2016). In the present
study, the consensual pupil light reflex will be measured using optimised stimulus conditions
and applying an open-loop Maxwellian view pupillometer with the pupil receiving the high
irradiance light stimulus being pharmacologically dilated to ensure a constant retinal
irradiance and to detect subtle melanopsin defect in non-seasonal depression that was not
detected by Laurenzo et al. (2016) in a mixed cohort of non-seasonal MDD and SAD.
2.3 PROJECTION OF ipRGCs TO MOOD CENTRES IN THE BRAIN
This research focuses on the ipRGC projections to the brain mood centres (Davis et al.,
2001; Hattar et al., 2006; Hattar et al., 2002; Matsumoto et al., 2007; Schmidt et al., 2011a)
based on the recent evidence in humans (Roecklein et al., 2013) and animal models (Legates
et al., 2012) that ipRGC function can be influenced in depressive disorders. Regulation of
mood may occur via direct innervation of ipRGCs to mood-regulating centres of the brain
(e.g., medial amygdala and lateral habenula) and their indirect projections to the mood
centres via the suprachiasmatic nucleus (SCN) (Hattar et al., 2006; Hattar et al., 2002;
Schmidt et al., 2011a).
Regulation of mood via the direct pathway is believed to take place via direct ipRGC
projections to the brain mood centres (see Figure 5), including the Medial amygdala (MA),
the lateral habenula (LHb), the locus coeruleus (LC), the ventral tegmental area (VTA), the
dorsal raphe nucleus (DRN) and the hippocampus (HC). It is not known which ipRGC sub-
type innervates these brain areas. These areas are known to have roles in the stress stimuli
response (Sara & Bouret, 2012; Schmidt et al., 2011a), behavioural adaptation and regulation
22
of mood in animals (Bayer & Glimcher, 2005; Matsumoto et al., 2007; Sara et al., 2012;
Schultz, Dayan, & Montague, 1997) and in humans (Campbell, Marriott, Nahmias, &
MacQueen, 2004; Russo & Nestler, 2013).
A recent study in a mouse model shows that depression-like behaviours can be
modulated through a direct aberrant light pathway to the brain mood centres, independent of
the circadian system (Legates et al., 2012). Nocturnal mice developed depression symptoms
after being exposed to 3.5 hrs light-dark ultradian cycles with light pulses during the animal’s
active phase (night). Depression in mice was not driven through the circadian pathway as 3.5
hrs light-dark pulses presented aberrantly (light pulse at night), as opposed to normal 12 hrs
light-dark pulse, did not affect the rhythms of the body temperature, general activity and the
central (SCN) and peripheral (liver) molecular circadian clocks (Legates et al., 2012).
Conversely, the ultradian aberrant light cycle did not depress the mice that lacked ipRGCs
(Legates et al., 2012). These findings are consistent with an earlier animal study in mice that
proposed that the SCN is not required to drive mood and cognition; surgical removal of
bilateral SCN in rats did not affect their performance during the swim test as it tests several
mobility behaviours (e.g., swimming, jumping, diving and head shakes) that distinguish
normal animal from those with depression (Tataroğlu, Aksoy, Yılmaz, & Canbeyli, 2004).
Light therapy in non-seasonal depression is thought to be driven via the direct mood
pathway independent of the circadian rhythm (Yamada, Martin-Iverson, Daimon, Tsujimoto,
& Takahashi, 1995). Although both morning and evening bright light altered the circadian
phase significantly in patients with non-seasonal depression, there was no relationship
between the changes in phase shifts and depression scores (Yamada et al., 1995) suggesting
that the direct mood pathway might have driven mood improvement with light exposure in
non-seasonal depression. The relationship among ipRGCs projecting to the brain mood
centres, environmental light exposure, and non-seasonal depression is yet to be determined.
23
The indirect ipRGC pathway in mood regulation originates from the SCN, which is the
central circadian clock. The SCN receives projections from M1 ipRGCs via the
retinohypothalamic tract (RHT) in humans (Hannibal et al., 2004) and mice (Baver et al.,
2008; Berson et al., 2002; Fernandez et al., 2016; Gooley et al., 2001; Gooley et al., 2003;
Hannibal et al., 2004; Hattar et al., 2002). In mice, the SCN receives 99% of the direct
innervations from ipRGCs, of which 80% of the projection is contributed by M1 and the
remaining 20% by M2 cells (Baver et al., 2008). IpRGCs also project to other brain circadian
centres like the intergeniculate leaflet (IGL), the ventral lateral geniculate nucleus (vLGN),
the ventrolateral preoptic area (VLPO), the lateral hypothalamus (LH) and the
subparaventricular zone (SPZ) for the circadian functions (Hattar et al., 2006). Unlike the
SCN, which is the central circadian clock, the VLPO, the LH and the SPZ are peripheral
circadian clocks that receive photic information directly from ipRGCs and indirectly via the
SCN for sleep regulation (Gooley et al., 2003; Hattar et al., 2006; Schmidt et al., 2011a). The
SCN also contributes to mood regulation via its projections to the brain mood centres such as
the VTA, the LHb, the LC and the HC (Figure 5 b).
24
Figure 5: Projections of ipRGCs to the brain centres in a mouse model.
(a) Projections of ipRGCs to mood centres (Green trace), circadian and sleep centres (Black
trace e.g., SCN, IGL, VLPO) and the pupillary centre (Blue trace, e.g., OPN). (b) Direct and
indirect projections of ipRGCs to brain areas that regulate mood and circadian
photoentrainment [Modified from (LeGates, Fernandez, & Hattar, 2014)].
These brain areas receive innervations from the SCN to regulate circadian rhythm
dependent mood and behaviour (Hattar et al., 2006; LeGates et al., 2014). The LC is the
principal site of norepinephrine synthesis, a neurotransmitter that has a role in processing the
responses to panic and stress (Sara et al., 2012). The HC has neuronal and hormonal
connections with the SCN [see Figure 5 (b)] and it is considered a site for learning and
memory encoding (Karatsoreos & McEwen, 2011; Russo et al., 2013). Experimental studies
have observed an impairment of hippocampal learning and memory in animals exposed to
acute and chronic circadian phase shifting (Craig & McDonald, 2008; Devan, Goad, Petri,
Antoniadis, Hong, Ko, Leblanc, Lebovic, Lo, & Ralph, 2001; Fekete, Van Ree, Niesink, & de
Wied, 1985) further suggesting that circadian rhythm disruption indirectly affects mood in
animals. Circadian rhythm and sleep disorders are common in depressive disorder
(Argyropoulos & Wilson, 2005; Borbély & Wirz-Justice, 1982; Wirz-Justice, 2006). Greater
degree of sleep fragmentation has been reported in both bipolar and unipolar depression than
in healthy individuals (Gillin, 1979). Sleep deprivation has further been shown to alter the
25
depressive state from depression to mania (Linkowski, Mendlewicz, Leclercq, Brasseur,
Hubain, Golstein, Copinschi, & Cauter, 1985). SAD is accompanied by circadian rhythm
disorders associated with shorter photoperiod and melatonin phase delay in winter (Lewy,
Sack, Miller, & Hoban, 1987; Wehr, Duncan, Sher, Aeschbach, Schwartz, Turner,
Postolache, & Rosenthal, 2001). Overall, mood disorders associated with circadian rhythm
disruption are believed to be driven by the SCN’s innervation to the brain mood centres.
The SCN is the pacemaker of the central circadian clock (Figure 6). It is a part of the
hypothalamic-pituitary-adrenal (HPA) axis that constitutes the body stress system (Chrousos,
1995, 2009; Karatsoreos et al., 2011; Nader, Chrousos, & Kino, 2010). On activation of the
HPA axis by stress, the adrenal gland cortex releases glucocorticoids (cortisol in humans and
corticosterone in rodents) (Bao, Meynen, & Swaab, 2008; Chrousos, 2009). Cortisol
increases calcium ion uptake at the synapses in order to increase the release of
neurotransmitters that subsequently decreases the stress (Schmidtke, 2013). Circadian
disruption slows down the HPA axis, resulting in a non-uniform production of the cortisol
hormone, leading to a poor response to the external stressors and depression (Chrousos, 1995;
Karatsoreos et al., 2011; Nader et al., 2010). Increased levels of cortisol releasing hormones
(CRH) and cortisol hormones are associated with increased signs and symptoms of
depression (Bao et al., 2008).
The SCN also acts as the central pacemaker of pineal melatonin production. Melatonin
secretion is regulated by the multi-synaptic neural pathways from the SCN (Moore, 1996;
Teclemariam‐Mesbah, Ter Horst, Postema, Wortel, & Buijs, 1999). Melatonin levels increase
in the evening in both nocturnal and diurnal animals. Exposure to bright light, specifically
short wavelength high irradiance light (5.58 x 1013 photons.cm-2) suppressing nocturnal
melatonin secretion (Brainard, Hanifin, Greeson, Byrne, Glickman, Gerner, & Rollag, 2001;
Thapan, Arendt, & Skene, 2001), indicates the role of ipRGCs in regulating melatonin
26
rhythm. The production and duration of active diurnal and nocturnal melatonin production is
altered in MDD such as bipolar disorder and SAD (Arendt, 1989; Crasson, Kjiri, Colin, Kjiri,
L’Hermite-Baleriaux, Ansseau, & Legros, 2004; Srinivasan, Smits, Spence, Lowe, Kayumov,
Pandi-Perumal, Parry, & Cardinali, 2006; Thompson, Franey, Arendt, & Checkley, 1988;
Wehr et al., 2001) suggesting that mood is related to the ipRGC and the SCN-driven pineal
melatonin rhythm in response to light. Therefore, circadian rhythm disruption affects mood
and cognition via the multiple neuronal and hormonal connections of the SCN to the brain
mood and circadian centres (see Figure 6).
27
Figure 6: The neuronal and hormonal connections of the SCN.
The SCN is the Master clock that receives photic input from ipRGCs and sends the neuronal
information (solid lines) to the peripheral clocks (blue symbols): the paraventricular nucleus
(PVN) and the thalamic relays. The PVN has neuronal connections with the anterior pituitary
and spinal cord that send neuronal and hormonal (dashed lines) connections to the peripheral
clocks (pineal gland, peripheral tissues, adrenal gland, pre-frontal cortex (PFC), HC and
MA). The PFC, HC and MA also send reciprocal information to the PVN and SCN for
restoring the homeostasis of the HPA axis (developed based on Karatsoreos & McEwen,
2011)
In conclusion, ipRGCs directly and indirectly (through the SCN) innervate brain areas
regulating light-mediated mood in humans and animals. The projection of M1 ipRGCs to the
brain mood centers in human is unknown. M1 ipRGCs project to multiple brain nuclei,
including few mood centers in rodents (Fernandez et al., 2016). If considered same for the
28
humans, measuring the function of M1 ipRGCs using the pupillometric paradigms, non-
image forming light inputs to the brain mood centers may be indirectly measured.
Light exposure is an established therapy in SAD (Burgess, Fogg, Young, & Eastman,
2004; Deppe, 2002; Glickman et al., 2006; Golden, Gaynes, Ekstrom, Hamer, Jacobsen,
Suppes, Wisner, & Nemeroff, 2005; Kräuchi et al., 1990; Lam, Levitt, Levitan, Enns,
Morehouse, Michalak, & Tam, 2006; Lewy, Bauer, Cutler, & et al., 1998; Terman & Terman,
2005; Wirz-Justice, Graw, Kräuchi, Gisin, Jochum, Arendt, Fisch, Buddeberg, & Pöldinger,
1993) and non-seasonal depression (Deltito, Moline, Pollak, Martin, & Maremmani, 1991;
Deppe, 2002; Epperson, Terman, Terman, Hanusa, Oren, Peindl, & Wisner, 2004; Even et
al., 2008; Friedman, Even, Dardennes, & Guelfi, 2004; Goel, Terman, Terman, Macchi, &
Stewart, 2005; Loving, Kripke, Elliott, Knickerbocker, & Grandner, 2005; Naus et al., 2013;
Terman et al., 2005; Tuunainen, Kripke, & Endo, 2004; Yamada et al., 1995), suggesting an
impaired light signaling within the retina or altered ambient external light exposure, or a
combination of both in MDD. This thesis aims to understand the relationship between ipRGC
function and environmental light exposure in depressive disorders and hypothesises that
patients with non-seasonal depressive disorders have impaired sensitivity of ipRGCs to
external light and/or are exposed to lower ambient light levels. The current literature on the
effect of ambient light exposure in depressive disorder is reviewed below.
2. 4 AMBIENT LIGHT AND DEPRESSION
Exposure to ambient environmental light, whether natural or artificial, is a key determinant of
human mental and physical well-being (Cao & Barrionuevo, 2015a, 2015b; Czeisler,
Johnson, Duffy, Brown, Ronda, & Kronauer, 1990; Czeisler, Kronauer, Mooney, Anderson,
& Allan, 1987; Czeisler & Waterhouse, 1995b; Smolders, De Kort, & Van den Berg, 2013).
Reduction in daylight exposure with seasonal changes has been associated with a decrease in
29
the production of brain-serotonin and vice versa (Lambert, Reid, Kaye, Jennings, & Esler,
2002). Although, the response from ipRGC is attenuated with recent light adaptation (Joyce
et al., 2016a; Wong et al., 2005), the effect of long term exposure to bright light on ipRGC
function is not known. Munch et al. (2016) showed a significantly greater PIPR and PLR
responses in summer than in winter suggesting lower pupil response with decreasing light
levels with season. The mechanism of change in light sensitivity of photoreceptors may be
modulated by the alteration of monoaminergic activity with season and light exposure
(Goldman, 2001; Lambert et al., 2002).
Circadian desynchronization has also been recognized to be associated with SAD; short
photoperiods during winter triggers winter depression (SAD) in some individuals and this is
hypothesised to be due to a dysfunctional ipRGCs requiring more light to remain euthymic
(Roecklein et al., 2013; Wehr et al., 2001). The dysregulation of melatonin and dopamine in
the retina and central nervous system of SAD patients (Lam & Levitan, 2000) may contribute
to the reduction in the PIPR that is modulated by melatonin levels (Münch, Léon, Crippa, &
Kawasaki, 2012; Zele, Feigl, Smith, & Markwell, 2011). Light exposure study in a normal
adult population in San Diego, California, USA found that individuals scoring higher on
atypical mood symptoms (like in SAD) spent less time in bright illumination (Espiritu,
Kripke, Ancoli-Israel, Mowen, Mason, Fell, Klauber, & Kaplan, 1994). This association
between a deficient natural light and depression in humans has been well established (Gou,
Lau, & Qian, 2015; Harb, Hidalgo, & Martau, 2015). Evidence also suggests that animals
exposed to short photoperiod, aberrant light cycle and night-time light demonstrate
depression-like symptoms that are reversed with antidepressants (Ashkenazy-Frolinger,
Kronfeld-Schor, Juetten, & Einat, 2010; Ashkenazy, Einat, & Kronfeld-Schor, 2009;
Bedrosian, Fonken, Walton, Haim, & Nelson, 2011; Fonken, Finy, Walton, Weil, Workman,
Ross, & Nelson, 2009; Fonken, Kitsmiller, Smale, & Nelson, 2012; Fujioka, Fujioka,
30
Tsuruta, Izumi, Kasaoka, & Maekawa, 2011; Legates et al., 2012; Workman, Manny,
Walton, & Nelson, 2011). Patients with SAD exposed to similar total daylight levels as those
without SAD, irrespective of the seasons (Graw et al., 1999; Guillemette et al., 1998; Oren et
al., 1994), have reduced melanopsin-mediated PIPR (Roecklein et al., 2013), indicates a
different ocular photoentrainment in patients with SAD than healthy individuals. In other
words, when light levels are low in winter, individuals with dysfunctional ipRGCs are
vulnerable to depression and those with healthy ipRGCs are not. Patients with severe visual
impairment involving retinal pathologies affecting ipRGC function such as glaucoma
(Adhikari et al., 2016b; Agorastos, Skevas, Matthaei, Otte, Klemm, Richard, & Huber, 2013;
Feigl et al., 2011; Kankipati et al., 2011) and age-related macular degeneration (Casten &
Rovner, 2008; Maynard et al., 2015) suffer from sleep disorders (e.g., increased or decreased
sleep duration and poor sleep quality) (Khurana, Porco, Claman, Boldrey, Palmer, &
Wieland, 2016; Pérez-Canales, Rico-Sergado, & Pérez-Santonja, 2016) and SAD (Madsen,
Dam, & Hageman, 2015). The relationship between ipRGC function, light exposure, and
depression in human is yet to be determined. Figure 7 shows a schematic linking the ipRGC
function in relation to the light exposure and depressive state based on the findings of human
and animal studies.
31
Figure 7: The schematic representation of current knowledge and hypothetical
relationships among ambient light, ipRGC function and depression.
Animals with normal ipRGCs exposed to short ultradian light cycle show depression-like
symptoms (left upper red quadrant) whereas those exposed to normal light cycle do not
(Legates et al., 2012) (left blue lower quadrant). Humans exposed to lower daylight in winter
and have a reduction in ipRGC function, suffer from winter depression (Roecklein et al.,
2013) (right upper red quadrant). It is hypothesised that abnormal ipRGC function found in
glaucoma (Feigl et al., 2011; Kankipati et al., 2011) and in age-related macular degeneration
(AMD) (Feigl et al., 2014; Maynard et al., 2015) may lead to depression as can be frequently
found in these common eye diseases (Agorastos et al., 2013; Casten et al., 2008) (right red
lower quadrant). In particular, depression and SAD have been associated with severe visual
impairment from retinal disorders (Madsen et al., 2015).
To determine the effect of ambient light exposure on patients with depression, light
exposure needs to be measured. To do this, an Actigraphy device (Actiwatch) can be used.
An Actigraphy device is an accelerometer-based watch-like device that monitors activity and
light exposure. Actigraphy is widely used to monitor sleep/wake cycle, circadian rhythm and
32
diagnose sleep disorder (Ancoli-Israel, Cole, Alessi, Chambers, Moorcroft, & Pollak, 2003;
Sadeh & Acebo, 2002). Geneactive (Activinsights, Kimbolton, Cambridgeshire, UK) and
Actiwatch 2 (Philips, USA) are the examples of ambulatory devices that are worn around the
wrist to measure light exposure at the wrist level.
Light exposure levels that are used to treat depression are duration dependent (Even et al.,
2008; Shirani & St Louis, 2009). Typically, light levels ≥ 2500 lux are used and duration of a
treatment session commonly decreases with an increase in illumination level (Even et al.,
2008). Most studies showing comparable treatment as psychopharmacotherapy in SAD
patients used illumination 2500 lux, 5000 lux and 10,000 lux for 2 hrs, 1 hr and ½ hr
respectively (Even et al., 2008; Gallin et al., 1995; Glickman et al., 2006; Haffmans et al.,
2008; Kräuchi et al., 1990; Meesters et al., 2011; Naus et al., 2013; Szabó et al., 2004;
Winkler et al., 2005; Wirz-Justice et al., 1999). The outcome of light treatment in comparison
to the conventional antidepressants in non-seasonal depression also showed similar trend
when treatment was done with light levels ranging from 2500 lux-10,000 lux (Beauchemin &
Hays, 1997; Corral, Wardrop, Zhang, Grewal, & Patton, 2007; Kripke, Mullaney, Klauber,
Craig Risch, & Christian Gillin, 1992; Lieverse et al., 2011; Martiny, Lunde, Unden, Dam, &
Bech, 2005; Naus et al., 2013; Wirz-Justice et al., 1999; Yamada et al., 1995). Successful
treatment outcome with these light levels may indicate that patients with depression may not
spend sufficient time in these light levels and/or they have impaired inner or outer retinal
photoreception. Although Glickman et. (2006) did not quantify the melanopic lux of blue
light used to treat depression in SAD, it is shown that blue light was as effective as white
light compared to red light. The photoreceptor pathway that broadband bright white light and
blue light trigger depression treatment in SAD is yet to be understood. Nevertheless, the
lower melanopsin sensitivity in patients with SAD (Roecklein et al., 2013) and the success of
light therapy with short wavelength (blue) light (Glickman et al., 2006) with high melanopic
33
excitation are suggestive that ipRGCs are contributing to the pathological mechanisms of
depression in SAD. The contribution of ipRGCs to non-seasonal depressive disorder and its
relationship to environmental light exposure remains to be determined and will be an aim of
this thesis.
There is evidence suggesting a role of ipRGCs in the outer retinal photoreceptors-
mediating image-forming functions via the intraretinal dopaminergic system (Joo et al., 2013;
Prigge et al., 2016). The image-forming functions of ipRGCs are thought to be driven via the
retrograde projection of the axons of ipRGC to the outer retina through the dopaminergic
system (Joo et al., 2013; Prigge et al., 2016). The next section reviews the current literature
on the image-forming retinal functions in depressive disorder.
2.5 RETINAL FUNCTION IN DEPRESSIVE DISORDERS
Electroretinogram (ERG) has been widely used to measure the electrical responses
from rod and cone in the outer retina and bipolar, muller and amacrine cells in the inner
retina. (Hamel, 2007; Miller & Dowling, 1970; Wachtmeister & Dowling, 1978). A typical
ERG response consists of a, b, c, d waves and oscillatory potentials origination from rod-
cone, ON bipolar and muller cells, pigment epithelium, OFF bipolar cells and amacrine cells
respectively (Hamel, 2007; Marmor & Hock, 1982; Wachtmeister et al., 1978). A recent
study optimized stimuli to match the ipRGC spectral sensitivity and showed that ERG
response can be elicited from ipRGCs (Kuze, Morita, Fukuda, Kondo, Tsubota, & Ayaki,
2016).
Most studies report lowered retinal sensitivity in patients with SAD than healthy
controls. While one study suggests there is no change in retinal sensitivity in SAD (Oren,
Moul, Schwartz, Alexander, Yatnada, & Rosenthal, 1993), Hebert et al., (2002, 2004) report
a seasonal variation in retinal sensitivity in humans with lower retinal sensitivity occurring
34
during winter (Hébert et al., 2004; Hébert et al., 2002). Indeed, lower electroretinogram
(ERG) b-wave amplitudes are reported in the patients with SAD compared to the normal
controls (Hébert et al., 2004; Hebert, Dumont, & Lachapelle, 2002). There is also a positive
correlation between the severity of seasonal mood changes and the ERG b-wave amplitude
(Hebert et al., 2002) in SAD. A reduction in ERG amplitude in SAD is an indicative of
impaired dopaminergic and serotonin (monoamines) neurotransmission in the retina and
central nervous system (Hébert et al., 2004; Lavoie, Illiano, Sotnikova, Gainetdinov,
Beaulieu, & Hébert, 2014).
Several other studies have proposed retinal hypersensitivity in SAD on ophthalmic
measures of visual function (Oren, Joseph-Vanderpool, & Rosenthal, 1991; Terman &
Terman, 1999; Wesner et al., 2006). The patients with SAD adapt more rapidly in dark than
the healthy controls (Oren et al., 1991). In addition, the patients with SAD have higher
photopic contrast sensitivities (CS) (Wesner et al., 2006) than the healthy people. The
scotopic (rod) and photopic (cone) thresholds in an incremental detection task are lower in
summer than in winter (Terman et al., 1999) and the thresholds are lower in the patients with
SAD than in healthy individuals in winter indicating that rod and cone pathways may be
supersensitive in the patients with SAD (Terman et al., 1999). This indicates outer retinal
photoreceptor sensitivity varies with season with higher sensitivity in summer than in winter
and in particular rod and cone pathway sensitivities in the patients with SAD are higher than
in healthy individuals in winter.
Similar to the patients with SAD, there are mixed findings as to the effect of non-
seasonal depression on visual function. While Wesner and Tan, (2006) observed increased
contrast sensitivity (CS) in non-seasonal depression measured using Gabor stimuli modulated
at higher spatial (12 cpd) and low temporal frequencies (2 Hz with Gabor target of 4 cpd),
Fam et al, (2013) demonstrated a reduction in contrast sensitivity measured with the Freiburg
35
visual acuity and contrast test (FrACT) compared to healthy control participants (Fam et al.,
2013). However, there was no difference in the mean pattern ERG (PERG) and full field
ERG (ffERG) amplitudes among both groups (Fam et al., 2013). The PERG amplitude was
significantly reduced in the patients with depression compared to the controls, with the
reduction being strongly correlated with the depression severity, but independent of the anti-
depressive medication (Bubl et al., 2010; Bubl et al., 2015). Bubl et al. (2015) further showed
that the VEP amplitude, a measure of visual cortical response, was reduced, but not to the
extent as the PERG based contrast amplitude reduction in major depression, indicating that
visual cortex in depression is affected and is preceded by the reduction in retinal contrast
sensitivity. Another study demonstrated a significant reduction in contrast sensitivity in MDD
and bipolar disorder patients when measured with 2 cpd Gabor targets, with the reduction
being independent of the severity and anti-depressive medication (Bubl et al., 2009). While,
methodological variations might have shown inconsistent visual contrast sensitivity findings,
depressive disorders have been most strongly associated with a reduction in visual contrast
sensitivity. This suggests, like SAD, people with non-seasonal depression also may have an
impaired intra-retinal dopaminergic system, analogous to Parkinson’s disease (Harnois & Di
Paolo, 1990; Ikeda, Head, & Ellis, 1994), which is associated with reduced visual contrast
sensitivity (Bodis-Wollner, Marx, Mitra, Bobak, Mylin, & Yahr, 1987; Ikeda et al., 1994;
Price, Feldman, Adelberg, & Kayne, 1992) that is improved following administration of
dopamine (Büttner, Kuhn, Patzold, & Przuntek, 1994). Hence, this study will also determine
the retinal visual function by measuring visual contrast sensitivity using conventional
ophthalmic charts.
36
2.6 EXPERIMENTAL AIMS AND HYPOTHESIS
This study compares intrinsically photosensitive Retinal Ganglion Cell (ipRGC)
function and outer retinal function in patients with non-seasonal depressive disorder to a
healthy age-matched control group. The pupil light reflex is used as an objective and non-
invasive biomarker of inner and outer retinal function; melanopsin function is isolated using
the ipRGC-mediated post-illumination pupil response (PIPR) and outer retinal function is
determined from the peak pupil constriction (peak PLR), transient pupil constriction
(transient PLR) and time to peak constriction amplitudes (time to peak PLR). Outer retinal,
cone-pathway mediated visual function is determined using a Pelli-Robson contrast
sensitivity charts (Pelli & Robson, 1988). Ambient light exposure is quantified using
Actigraphy in terms of the average day and night light exposure (per minute, per hour) and
time spent daily under bright light levels (≥ 2500 lux, ≥ 5000 lux and ≥ 10,000 lux) in
patients with depression and age-matched controls. The aims and hypotheses of the study are
as follows:
Aim 1
To quantify the relationship between the post-illumination pupil response (PIPR), transient
and peak pupil constriction amplitude, time to peak constriction amplitude and the ambient
environmental light exposure in individuals with and without non-seasonal depression. It is
hypothesised that the PIPR and PLR amplitudes will be lower in patients with non-seasonal
depression than in healthy control participants. The ambient daylight exposure levels are
predicted to be lower in patients with non-seasonal depression compared to the healthy
control participants. The PIPR and PLR amplitudes will positively correlate with the light
exposure levels among the patients with depression.
37
Aim 2
To determine the visual contrast sensitivity in individuals with and without non-seasonal
depression. It is hypothesised that the patients with depression will have lower contrast
sensitivity scores than the healthy control participants. Reduction in contrast sensitivity will
positively correlate with the transient PLR among the patients with depression.
38
CHAPTER 3: EXPERIMENTAL METHODS
3.1 ETHICS STATEMENT
All procedures were approved by the QUT Human Research Ethics Committee
(Approval Number: 1500000597) and followed the Declaration of Helsinki. All participants
signed an informed consent before participation.
3. 2 PARTICIPANTS
Participants consisted of two groups; participants with non-seasonal depression
(depression group) and healthy individuals without depression (control group). All
participants in the depression group were taking medications for depression, including
selective serotonin reuptake inhibitors (SSRIs), serotonin and norepinephrine reuptake
inhibitors (SNRIs), monoamine oxidase inhibitors (MAOI), agomelatine, and antimanic
drugs. A summary of the inclusion criteria for the two groups and the assessment procedures
is provided in Table 1. The depression group was required to have (i) current Diagnostic and
Statistical Manual of Mental Disorders, 4th Edition (DSM-IV) MDD assessed using the Mini
International Neuropsychiatric Interview (MINI), version 6.0.0, (ii) at least mild levels of
depressive symptoms in the last 2 weeks on the Beck Depression Inventory-II and (iii) a
negative screen on both clinician-rated and self-report measures of SAD (winter depression),
including the Hamilton Depression Rating Scale-Seasonal Affective Disorder (HDRS-SAD)
and the Seasonal Pattern Assessment Questionnaire (SPAQ). The HDRS-SAD and SPAQ
were administered to the participants who had recurrent depression on the MINI. Those with
recurrent MDD with at least two depressive episodes during the winter in the past two
consecutive years with remission in the summer were identified as meeting the DSM-IV
criteria of SAD. People with self-reported history of a psychotic or bipolar disorders were
39
excluded. The presence of bipolar and psychotic disorders was also confirmed with MINI 6.
People with a cognitive impairment and/or intellectual disability were also excluded as they
were unlikely to understand the purpose of the research in order to provide informed consent.
The healthy control group was required to have a negative screening on all measures of
depressive symptoms and disorders and no lifetime history of depression.
On the ophthalmic assessment (Table 1), all participants had a best corrected visual
acuity (BCVA) better than 6/6, normal colour vision, no previous intraocular surgery, no
ocular disease and no diabetes. All participants had a colour vision examination with a
L’anthony D-15 test, slit-lamp examination, anterior chamber angle assessment, a pupillary
light reflex screen with a torchlight, indirect ophthalmoscopy and optical coherence
tomography (OCT) (Nidek RS-3000 OCT Retiscan Advanced, NIDEK CO., LTD) to detect
any ocular pathology.
40
Table 1: Study inclusion criteria and assessment procedures
Examination Instrument Inclusion criteria (Non-seasonal
depression)
Inclusion criteria
(healthy controls)
Psychology MINI MDD (Current) and no psychotic
and bipolar disorder
No MDD and
No psychotic and bipolar
disorder
HDRS-SAD Recurrent depressive episodes
(MINI) with score of > 19 on the
HDRS and ≤ 4 on the atypical
subscale
A score of < 19 on the
HDRS and ≤ 4 on the
atypical subscale
BDI-II
SPAQ
Score > 10
Recurrent depressive episodes
(MINI) with GSS < 11, not feeling
worst in the winter months (June,
July and August)
Score < 9
GSS < 11, not feeling
worst in the winter
months (June, July and
August)
Cognition Observation No intellectual disability and
cognitive impairment
No intellectual disability
and cognitive impairment
Visual Acuity Bailey-Lovie Log
MAR Chart
6/6
Colour Vision L’anthony
Desaturated Panel
D-15 test for
colour vision
Normal colour vision
Ophthalmoscopy Binocular Direct
Biomicroscopy (90
D/78D lenses)
Normal retina and optic disc
IOP I-Care Tonometer ≤ 21 mmHg
Ocular Media Nikon Slit Lamp
Biomicroscope
No corneal and lenticular opacities
Macula and
Optic Disc
Optical Coherence
Tomography
(OCT)
Normal macular and RFNL thickness
BDI-II, Beck Depression Inventory, 2nd edition; GSS, Global Seasonality Score; HDRS-SAD,
Hamilton Depression Rating Scale -Seasonal Affective Disorder; MINI, Mini International
Neuropsychiatric Interview; SPAQ, Seasonal Pattern Assessment Questionnaire;
41
In accordance with the human research ethics approval (Approval Number:
1500000597), patients with depression were approached and recruited from the Queensland
University of Technology (QUT) Psychology and Counselling, Health clinic and General
practices, two private psychology clinics in Brisbane (Psychology Consultants), depression
support groups around the Brisbane central business district and via newspaper
advertisements. Advertisements were distributed via flyers, student emails and word of
mouth within QUT to recruit both the depression group and age and gender matched healthy
controls. Psychologists were provided with the study details and flyers to distribute to the
potential participants with depression. They were followed up and reminded through regular
meetings, emails and telephone contacts. Figure 8 displays the study protocol.
42
Figure 8: The study protocol.
The study consisted of 2 visits. During the 1st visit (Blue), participants provided informed
consent and were screened for ocular and mental health and received a Geneactive device
(Actigraph). During the 2nd visit (green), participants underwent the pupillometry (see text for
detail).
3.3 ACTIGRAPHY
All participants were provided with a light sensor watch (Geneactive, Activinsights,
Kimbolton, Cambridgeshire, UK) for 2 weeks from the months November 2015 through
August 2016 in Brisbane, Australia (27.5° S, 153.0° E). They were instructed to wear the
device on the non-dominant wrist continuously during the 2 weeks to determine the daily
light exposure and sleep-wake timings and duration. Each participant was asked to maintain a
log of bedtime, time to sleep after going to bed, number of times awake after bed, maximum
number of minutes awake after going to the bed (between sleep), final wake time, number of
day naps and maximum number of hours of day naps. After two weeks of the wear, the raw
43
data were extracted and imported to an Excel spreadsheet sleep macro constructed by
Activinsights (Kimbolton, Cambridgeshire, UK) that allows interpreting the sleep-wake
timings, sleep length, mid-sleep time, Geneactive wear times and minutes of light exposure
(lux). The mid-sleep time was computed to compare the circadian phase and chronotype
between the MDD and control groups (Martin & Eastman, 2002; Terman, Terman, Lo, &
Cooper, 2001; Zavada, Gordijn, Beersma, Daan, & Roenneberg, 2005). Using the macro
spreadsheet, the minutes and hours of day and night light exposure (lux) for 14 days (20,160
min) and light exposure duration to broadband light (≥ 10,000 lux, ≥ 5000 lux, ≥ 2500 lux)
that are the illuminance ranges recommended for depression light therapy (Even et al., 2008;
Gallin et al., 1995; Glickman et al., 2006; Haffmans et al., 2008; Kräuchi et al., 1990;
Meesters et al., 2011; Naus et al., 2013; Szabó et al., 2004; Winkler et al., 2005; Wirz-Justice
et al., 1999) were computed. To account for the differences in light exposure due to different
wake times among the participants, circadian time was normalized to individual wake time.
Sleep length and sleep efficiency were derived from the sleep macro and sleep onset latency
(time to sleep after going to bed) was derived from the participants’ self-reported sleep
charts.
The time to first light, last light and the global solar exposure (GSE) of Brisbane,
Australia were recorded for every day for each participant from the websites of the
WillyWeather and Australian Government, Bureau of Meteorology, respectively (Australian
Government, 2016; WillyWeather, 2016). Light exposure artefacts were excluded. Artefacts
were determined by light exposure data generated over non-wear times of the Geneactive
device and the data indicating complete darkness with activity during the day when the
person was not in bed. Artefacts could occur by participants not wearing the watch and by
their clothes covering the light sensors. However, artefacts were minimized at best by
instructing the participants not to remove the watch or cover the light sensor with clothing
44
throughout the study period. The participants were also followed up for the compliance at the
final visit.
3.4 PSYCHOLOGICAL ASSESSMENTS FOR DEPRESSION
3.4.1 MINI INTERNATIONAL NEUROPSYCHIATRIC INTERVIEW
The MINI 6 was used to assess for the presence of 12-month DSM-IV diagnosis of
depression and anxiety disorders. (Lecrubier, Sheehan, Hergueta, & Weiller, 1998). It is a
brief diagnostic structured interview [average time to administer = 16.4 min (Pinninti,
Madison, Musser, & Rissmiller, 2003)] which can be easily administered by non-specialized
interviewers. The Mini has been validated against the Composite International Diagnostic
Interview (CIDI) and the Structured Clinical Interview for DSM-IH-R (SCID) to assess for
the presence of 17 disorders based on DSM-IV diagnostic criteria (Lecrubier, Sheehan,
Weiller, Amorim, Bonora, Harnett Sheehan, Janavs, & Dunbar, 1997). It contains a
suicidality section that assesses whether the individual has ‘seriously thought about
committing suicide’ (suicidal ideation), ‘made a plan for committing suicide’ (suicide plan)
and ‘attempted suicide’ (suicide attempt) in their ‘lifetime’ and ‘within the past month’. A
score of 1-8 indicates they are at low risk, 9-16 points indicated moderate risk and > 17
points indicates high risk. Participants with high suicidal risk as assessed with MINI were not
included in the study.
3.4.2 THE BECK DEPRESSION INVENTORY-II (BDI-II)
The Beck Depression Inventory-II (BDI-II) is a 21-items self-report measure of the
severity of depression symptoms (Beck, Steer, Ball, & Ranieri, 1996). BDI-II has been
validated in 414 students showing high internal consistency and validity (Storch, Roberti, &
45
Roth, 2004). Each question is rated on a 4-point scale that ranged from 0 = no depression
symptom to 3 = obvious depression symptom to derive a total score indicative of depression
severity (See Table 2 for interpretation).
Table 2: BDI-II scores and depression Severity
BDI-II Scores Severity of Depression
0-9 Normal
10-16 Mild Depression
17-29 Moderate Depression
30-63 Severe Depression
BDI-II, Beck Depression Inventory, 2nd edition
3.4.3 SEASONAL AFFECTIVE DISORDERS
Those participants who met criteria for recurrent depression on the MINI 6 (recurrent
MDD with at least two depressive episodes during winter in the past two consecutive years
with remission in the summer) completed both clinician-rated and self-report measures of
SAD to exclude patients with SAD.
3.4.3.1 THE HAMILTON DEPRESSION RATING SCALE -SEASONAL
AFFECTIVE DISORDER VERSION (HDRS-SAD)
The HDRS-SAD consists of two clinician-rated scales: the 21-item Hamilton
Depression Rating Scale (HDRS) and 8-item atypical features of SAD (ATYP) scale
(Williams, Link, Rosenthal, & Terman, 1988). A score of at least 19 on HDRS and a score of
4 or more on the 8 ATYP symptom score was indicative of SAD (Terman, Terman, &
Rafferty, 1990). The inter-rater reliability trial of HDRS-SAD shows relatively low inter-rater
discrepancy (5.6%), specially with items- “”depressed mood”, “work and activities”, “middle
46
insomnia”, and “hypochondriasis” and atypical (SAD) items- “fatigability” and
“Hypersomnia” (Rohan, Rough, Evans, Ho, Meyerhoff, Roberts, & Vacek, 2016). Given,
some degree of discrepancy recorded with HDRS-SAD, the diagnosis of MDD and SAD will
be made in conjunction with MINI, BDI-II and SPAQ that are shown to have high internal
consistencies (Lecrubier et al., 1997; Magnusson, Friis, & Opjordsmoen, 1997; Storch et al.,
2004).
3.4.3.2 THE SEASONAL PATTERN ASSESSMENT QUESTIONNAIRE
(SPAQ)
The self-report SPAQ assesses the degree of seasonal variations of mood and behaviour
on six items including mood, sleep duration, social activities, weight, appetite and energy
rated on a 4-point scale (no change = 0 to extremely marked change = 4). A global
seasonality score (GSS) of > 11 is indicative of SAD, and requires individuals to “feel
worst” in winter (July and/or August), compared to summer (January and/or February) and to
experience at least moderate problems with season change (Kasper, Wehr, Bartko, Gaist, &
Rosenthal, 1989).
The participant’s level of distress was also monitored throughout the study procedure
(as indicated by voice tone/affect/self-reported mood). Participants were directly asked “are
you feeling ok?” if they were feeling any distress at the end of the study experiment. Any
participant reporting distress was debriefed by using a debriefing protocol (Appendix 9.0).
3.5 PUPILLOMETRY
The PLR and PIPR were measured with an extended Maxwellian view open-loop
pupillometer that was custom-built and calibrated for wavelength and irradiance in the
Medical Retina Laboratory at the Institute of Health and Biomedical Innovation (IHBI), QUT
47
(Adhikari et al., 2015b; Feigl et al., 2014). The pupillometer consists of narrow band light-
emitting diode (LED) light sources (Figure 9) projected in the pupil plane of the left eye via
two Fresnel lenses (100 mm diameter, 127mm and 70 mm focal lengths respectively,
Edmund Optics, Singapore) and a 5° light-shaping diffuser (Physical optics Corp., Torrance,
CA, USA) (Adhikari et al., 2015b).
Figure 9: The Maxwellian view open-loop pupillometer system
A Maxwellian view pupillometer system consists of an LED light source placed in a rotating
wheel positioned in the focal plane of the 1st Fresnel lens (F1). The LED projects a divergent
beam to F1 which produces a parallel beam after refraction and projects to the 2nd Fresnel lens
(F2) which is positioned such that rays after refraction from (F2) focuses on the pupil plane of
the left eye. The infrared (IR) LED illuminates the right eye via reflection through two
parallel mirrors (M). The camera (C) records the pupil light reflex of the right eye. An
aperture (A) is placed at the focal planes of F1 and F2 which controls the field of view of the
system.
48
The left pupil was dilated with 0.5% Tropicamide (Minims; Chauvin Pharmaceuticals
Ltd., Romford, UK). The participant was dark adapted for 10 minutes in a darkened
laboratory (< 1 lux) and the consensual pupil light reflex in the right eye was recorded under
an infrared LED illumination (851 nm). A custom developed Matlab software (version
7.12.0; Mathworks, Nitick, MA, USA) was used to control the stimulus presentation and
analyse the pupil light reflex. The pupillometry procedure was done between 10 AM to 5 PM
to minimize the effect of circadian variation of the PIPR amplitude in humans (Münch et al.,
2012; Zele et al., 2011).
In accordance with standard procedures developed and validated in the Medical Retina
Laboratory (Adhikari et al., 2015b; Adhikari et al., 2016b), the pupil light reflex was
measured under high melanopsin and low melanopsin excitation conditions. The high
melanopsin excitation stimulus included a narrow-band blue appearing light (464 nm) with
20 nm band-width at half maximum, 2.9 log cd.m-2 luminance, 15.5 log quanta.cm-2.s-1
corneal irradiance and 8601.7 α-opic lux (Lucas, Peirson, Berson, Brown, Cooper, Czeisler,
Figueiro, Gamlin, Lockley, O’Hagan, Price, Provencio, Skene, & Brainard, 2014). The low
melanopsin excitation control stimulus was narrow-band red appearing light (637 nm) with
22 nm band-width at half maximum, 3.1 log cd.m-2 luminance, 15.5 log quanta.cm-2.s-1
corneal irradiance and 0.5 α-opic lux. The red light stimulus (637 nm) was used to determine
the outer retinal photoreceptor contribution to PLR and control fatigue in PIPR (Gamlin et al.,
2007; Kankipati et al., 2010; Markwell et al., 2010; Zele et al., 2011). The measurement for
each wavelength was repeated twice with an interval minimum of ~ 2 minutes between
stimuli so that the sustained PIPR of the first recording did not affect the subsequent
recordings (Adhikari et al., 2015b). The stimuli were alternately presented to account for the
effect of melanopsin bistability (Mure, Rieux, Hattar, & Cooper, 2007). Figure 10 shows the
pupillometry protocol of stimuli presentation and recording.
49
Figure 10: The pupillometry protocol used in the experiment
Following 10 mins of dark adaptation (black) to the laboratory illumination (< 1 lux), the
baseline pupil diameter was recorded for 10 s (gray) which was followed by the pupil
recording with a 1 s long wavelength light (red) stimulus. The post-illumination pupil
recording was done for 40 s after light offset (gray). The procedure was repeated for the short
wavelength light (blue) stimulus after 2 mins break in dark. Two repeats for each of the red
and blue light stimulus were recorded with 2 mins break between the repeats.
Two PIPR metrics were quantified: the 6 s PIPR and the plateau PIPR amplitudes. The
net PIPR (Kankipati et al., 2010; Roecklein et al., 2013) was not reported because it has both
higher intra- and inter-individual variation than the plateau and 6-second metrics (Adhikari et
al., 2015b). The maximum pupil constriction (PLR), transient PLR and time to peak
constriction in response to short (blue) and long (red) wavelength stimuli were analysed for
all participants. Custom developed Matlab software (version 7.12.0; Mathworks, Nitick, Ma,
USA) was used to control the stimulus presentation, analyse the pupil light reflex metrics and
linearly interpolate the missing data points due to blinks.
3.5.1 PUPILLOMETER CALIBRATIONS
The spectroradiometric calibrations were performed for the red and blue LEDs. The
spectral outputs of the LEDs were measured with a spectroradiometer (StellarNet, Tampa,
FL, USA) positioned in the optical system at the position of the eye. The spectral output
normalized to the peak irradiance for blue and red LEDs is shown in Figure 11.
50
3 5 0 4 0 0 4 5 0 5 0 0 5 5 0 6 0 0 6 5 0 7 0 0 7 5 0
0 .0
0 .2
0 .4
0 .6
0 .8
1 .0N
orm
ali
se
d I
rra
dia
nc
e (
Wa
tts
.cm
-2
. s-1)
W a v e le n g th (n m )
max = 4 6 4 n m 6 5 8 n mmax =
Figure 11: The spectral output of the LEDS used in the pupillometer.
The spectral output calibration of blue (max = 464 nm) and red (max = 658 nm)
normalized to their peak irradiance are shown.
The irradiance of the LEDs was measured with a calibrated ILT 1700 Research
Radiometer (International light technologies, Inc., Peabody, MA, USA) (Nygaard &
Frumkes, 1982) at the plane of the artificial pupil which gave a representation of actual eye
position during the pupillometry procedure. Calibrations were done in a dark room 10 mins
after turning on the radiometer. The radiometer was first set at zero to the dark light. The
irradiance levels were controlled by adjusting the 8-bit Digital to Analogue Converter (DAC)
values using Matlab software manually. The DAC value ranges from 0 (minimum) to 225
(maximum). The measurement was done by varying the DAC values from 1 to 225 in both
ascending and descending order for both wavelengths. The corresponding radiometer
readings (irradiance) were measured and 3 measurements were averaged for each DAC value.
A linear trendline was fitted to the irradiance as a function of DAC values (Figure 12) were
calculated for required irradiance levels using the following equation:
Y = mx + c (Equation 1)
51
Where
Y = irradiance, x = DAC value, m = slope of the trendline, c = intercept of the trendline to the
y-axis.
0 5 0 1 0 0 1 5 0 2 0 0 2 5 0
0 .0 0 0 0
0 .0 0 0 5
0 .0 0 1 0
0 .0 0 1 5
0 .0 0 2 0
D A C V a lu e
Ou
tpu
t (W
att
s.c
m-2)
Figure 12: The irradiance output calibration of the red and blue LEDs.
The irradiance output (watts.cm-2) as a function of DAC values for short wavelength (blue)
and long wavelength (red) stimuli LEDs.
Radiometric unit of power (watts. cm-2.s-1) was converted to an actinometric unit of
quanta (log quanta.cm-2.s-1) by following the relationships explained below.
The relationship between quanta (Φ) and radiant power (φ) is given by
Φ = φ*hc (Equation 2)
52
Where is the wavelength in meters, h is the planks constant (6.626 x 10-34) and c is the
speed of light (2.998 x 108 m/s). For a point light source, quanta flux (quanta/s) and radiant
power (Watts) are related to irradiance (Watts/m2) and quanta irradiance (quanta/m2/s) by
φ = ER*A and
Φ = Eq*hc
Where ER is irradiance, Eq is quanta irradiance and A is the area of the surface that receives
light. By combining the above equations,
ER = Eq *hc (Equation 3)
3.5.2 PUPILLOMETRY DATA ANALYSIS
The pupil light reflex data were fitted with linear and exponential models (Feigl et al.,
2011; Zele et al., 2011). The first 10 s pre-stimulus phase, defined as the baseline pupil
diameter (BPD) which was fitted with a constant. The second phase started with the light
onset reaching up to the maximum constriction (PLR) from where the pupil partially redilated
and plateaued to give rise to the PIPR. This PIPR phase that started at stimulus offset was
fitted with an exponential model described by the following equation, by minimising the
sums of square differences in Microsoft Excel 2010 (Microsoft Corporation) using the Solver
analysis tool:
y = S * Exp (k * x) + P (Equation 4)
Where S is a constant, k is the pupil redilation velocity (Global rate constant; GR) in mm/s, x
is time in second, and P is the plateau of the PIPR in mm (Feigl et al., 2011). The 6 s PIPR
amplitude was determined as the pupil diameter at 6 s after light offset on the exponential
model fitted to the PIPR phase. The PLR and PIPR amplitudes were normalized to the dark-
53
adapted baseline pupil diameter to account for the differences that would occur due to
differences in baseline pupil diameter.
3.6 CONTRAST SENSITIVITY
Contrast sensitivity (CS) was measured in all participants with a wall mount Pelli-
Robson chart (Clement Clarke International Ltd.) (Pelli et al., 1988). The Pelli-Robson chart
is a 90 x 60 cm chart that consists of 8 rows of letters with different contrast. Each row
consists of 6 letters with 3 letters (triplet) on the left with higher contrast than the triplet on
the right. The contrast decreases downwards and towards the right. The highest left triplet
letters have the highest contrast (1 or 100%) and the lowest right triplet letters have the
lowest contrast (0.006 or 0.6%). All letters in the chart are of equal size, subtending 1 cycle
per degree (cpd) at the recommended testing distance of 1 m (Pelli et al., 1988). Photopic
contrast sensitivity was tested in the left eye for all participants. The chart illuminance on
average was 450 lux. The contrast sensitivity score was recorded for the last triplet of which
at least 2 letters were correctly reported in accordance with the triplet scoring procedure
suggested by Pelli et al, (1988). Contrast sensitivity was recorded as log contrast sensitivity
(Log CS).
3.7 SAMPLE SIZE CALCULATIONS AND POWER ANALYSIS
Sample size calculation was done based on the means and standard deviations of a
recent SAD study that showed significant results in the PIPR amplitude in a sample of 15
participants (Roecklein et al., 2013). A minimum of 45 participants was calculated to detect a
significant difference in the PIPR with an effect size of 0.70 and power of 0.95 at a
significance level of 0.05.
54
3.8 STATISTICAL ANALYSIS
Statistical data analysis was done with IBM SPSS 22 and GraphPad Prism (GraphPad
Software, Inc., CA, USA). Prior to the data analysis, the data were screened to assess the
assumptions for parametric testing. Light exposure, quantified in terms of the average day
and night light, hourly light exposure and number of minutes of light exposure derived from
the Geneactive macro, and the PLR (peak constriction amplitude, transient PLR and time to
peak constriction) and the PIPR (6 s and plateau PIPR) metrics were tested for normality
using Shapiro-Wilk test. Independent t-test (for parametric distribution) and Mann-Whitney
test (for non-parametric distribution) were used to determine the difference in daily light
exposure between the groups. Mean and SD were reported for parametric data and median
values were presented for non-parametric data. The effect of medications on the PLR and
PIPR was analysed by comparing these parameters separately for each medication between
patients taking the medication and healthy controls. Hourly light exposure (lux) values were
log transformed to fulfil the assumption of parametric tests. A factorial univariate one-way
ANOVA was used to analyse the interaction of hourly light exposure among the groups for
time of the day and seasons. Pearson’s (for parametric data) and Spearman’s (for non-
parametric data) correlation coefficients were calculated to analyse the effects of PIPR on
sleep parameters and depression severity and the effect of seasonal variation in light levels on
the daily exposure levels within the groups. The analysis of covariance was done for gender,
photoperiod and GSE to eliminate the potential effect of these factors on the light exposure
and PIPR amplitude. The effect of depression severity on the visual contrast sensitivity was
analysed with a linear regression model. The statistical significance was determined based on
whether or not the slope of the best-fitting linear regression line was significantly different
from zero using an F-test (95% confidence interval, p < 0.05).
55
CHAPTER 4: RESULTS
4.1 PARTICIPANT CHARACTERISTICS
All participants were recruited during the months November 2015 to August 2016.
Based on the season, the recruitment period was classified as summer dominating months
(Nov-Mar) or winter dominating months (Apr-Aug). A total of 22 participants was recruited.
Thirteen participants were recruited during the summer dominating months (depression, n =
4; control, n = 9) and nine during the winter dominating months (depression, n = 4; control, n
= 5). A total of 14 patients with depression were referred for participation in the study. Of
these 14 patients, six were excluded as two patients had glaucoma, two had a history of
psychosis and two did not have a current major depressive disorder (MDD) on the MINI.
Table 3 shows the characteristics of the patients with depression.
Table 3: The characteristics of the patients with non-seasonal depression
SN Sex Age
(Y)
MDD Diagnosis* Diagnosis
Duration
Episode Severity**
1 F 23 Current MDD 2 years 1 Moderate
2 F 34 Current MDD 3 years 1 Moderate
3 M 39 Current MDD with panic
disorder lifetime with
agoraphobia and social phobia
3 years 2 Severe
4 F 18 Current MDD with panic
disorder lifetime with
agoraphobia
1 Year 1 Moderate
5 F 36 Current MDD 21 years 1 Severe
6 F 57 Current MDD with panic
disorder lifetime with
agoraphobia and social phobia
21 Years 1 Mild
7 F 61 Current MDD with post-
traumatic stress disorder
18 Years 2 Moderate
8 F 32 Current MDD with panic
disorder lifetime without
agoraphobia
2 Years 2 Moderate
MDD, major depressive disorder
*Diagnosis based on the Mini International Neuropsychiatric Interview, Version 6 (MINI 6)
**Severity based on the Beck Depression Inventory, Version II
56
A total of 16 control subjects with a negative screen for a current depressive disorder were
recruited. Two control subjects with family history of depression were excluded. One female
control participant was excluded from the pupillometry analysis as she was unable to
maintain her eye wide open during the procedure such that the pupil margins were not
tracked by the Matlab software. This resulted in eight patients (7 females /1 male, median age
= 35 years) with depression and 14 healthy controls (7 females / 7 males, median age = 29
years) for light exposure analysis and 13 controls (6 females / 7 males, median age = 29
years) for pupillometry analysis. The time at which pupillometry procedure was done
between the groups were not significantly different (p = 0.47). The groups did not differ in
age (p > 0.05, Mann-Whitney test). The current study has a higher proportion of females
(87.5%) than the general female estimates among the Australian population with depression
(63.6%) (Wilhelm, Mitchell, Slade, Brownhill, & Andrews, 2003). The proportion is
consistent with the recent studies with patients with SAD (86.8%) (Roecklein et al., 2013)
and MDD including SAD (79%) (Laurenzo et al., 2016). There was no significant group
effect of the gender on the pupil and light exposure measures (p > 0.05, Mann-Whitney test).
There was also no significant difference in PIPR amplitude (F 1,16 = 0.6, p = 0.4) and mean
daylight exposure (F 1,16 = 0.8, p = 0.4) between the groups when gender was analysed for a
covariate.
The mean BDI-II scores were 25.8 ± 5.7. Although three patients with depression met
MINI criteria for recurrent depression and had HDRS-SAD atypical scores above the clinical
cutoff for SAD, these patients were not excluded from study as they did not have winter
depression with worst mood during the winter months on the SPAQ. Their GSS was also
below the clinical cut for SAD on the SPAQ (see Table 4).
57
Table 4: Depression scores on SAD measures in patients with recurrent depressive episodes on
the MINI
SN MINI No. of
episodes
(n = 8)
HDRS (21
item)
(n = 3)
HDRS-SAD
(Atyp)
(n = 3)
SPAQ
(GSS)
(n = 3)
(SPAQ)
winter worst
(n = 3)
1 1
2 1
3 2 23 10 3 NO
4 1
5 1
6 1
7 2 10 6 3 NO
8 2 9 8 9 NO
GSS, global seasonality score; HDRS-SAD, Hamilton depression rating scale for seasonal affective
disorder; MINI, Mini international neuropsychiatric interview; SPAQ, Seasonal pattern assessment
questionnaire
All patients with depression were on psychotropic medication for depression. The
patients with depression had current treatment with selective serotonin reuptake inhibitors
(SSRIs) (87.5%) and/or combined with norepinephrine reuptake inhibitors (SNRIs) (25%),
monoamine oxidase inhibitors (MAOI) (12.5%), agomelatine (12.5%), anticholinergic
(Nortriptyline) (12.5%) and antimanic (25%) drugs. Although two patients with depression
were taking antimanic drugs (Lithium carbonate) as mood stabilizers, they neither had self-
report history of bipolar disorder nor were assessed as bipolar disorder in the MINI. One
female participant in the depression group was taking hormonal contraceptive and one was
under hormonal therapy for thyroid dysfunction. None of the control participants were taking
any medication during the study. As most of the patients with depression in the study were
taking SSRIs and mixed reports of their effect on the resting pupil diameter (increased or
decreased baseline pupil diameter) have been reported (Bitsios, Szabadi, & Bradshaw, 1999;
Phillips, Bitsios, Szabadi, & Bradshaw, 2000; Schmitt, Riedel, Vuurman, Kruizinga, &
Ramaekers, 2002), the PLR and PIPR data of the patients were normalized to their individual
dark adapted baseline to nullify the effect of the differences in the resting pupil diameters.
The antidepressants of the class SNRI are expected to affect the baseline pupil diameter,
58
pupil constriction amplitude and time to pupil recovery after stimulus offset (Bitsios et al.,
1999; Phillips et al., 2000; Siepmann, Ziemssen, Mueck-Weymann, Kirch, & Siepmann,
2007). Hence, a separate analysis was performed to examine the differences in PLR and PIPR
between the patients with depression not taking the SNRIs (n = 6) and the control group (n =
13) (see sections 4.2 and 4.3). Although, the effects of anticholinergic drugs on the pupil
reflex have been reported (Bye, Clubley, Henson, Peck, Smith, & Smith, 1979; Loewenfeld
et al., 1993), the drug (Nortriptyline) taken by one patient in this study has been shown to
have no effect on the resting pupil diameter and the pupil light reflex (Åsberg & Germanis,
1972; Bye et al., 1979). Hence, separate analysis of the effect of Nortriptyline was not
examined. The effects of other less commonly used antidepressants (MAOI and agomelatine
by one patient and antimanic drug by 2 patients) on the pupil are not known. Nevertheless,
there was no effect of these medications on the main outcome parameter, the 6 s PIPR
amplitude among the patients with depression (P < 0.000, Mann-Whitney test).
The light exposure data were excluded as artefacts in 0.8% and 4% of the patients with
depression and control participants, respectively. The groups did not differ in the global solar
exposure (GSE) (p > 0.05, Mann-Whitney test) and the photoperiod (p > 0.05, independent t-
test) during the study period. There was no significant difference in PIPR amplitude
(Photoperiod, F 1,16 = 0.5, p = 0.5, GSE, F 1,16 = 0.07, p = 0.8) and mean daylight exposure
(Photoperiod, F 1,16 = 0.02, p = 0.9, GSE, F 1,16 = 0.1, p = 0.7) between the groups when
photoperiod and GSE were analysed for covariates. Table 5 shows the demographic and solar
exposure characteristics of the participants in both groups. The GSE calculated over the study
period during the summer dominating months (median GSE = 6.1 KWh.m-2) was
significantly higher (P < 0.000, Mann-Whitney test) than that during the winter dominating
months (median GSE = 3.9 KWh.m-2).
59
Table 5: The demographic and solar exposure characteristics among the patients with
depression and healthy control participants
Control (n = 14) Depression (n = 8) P value
Age (y) 18-53 years (median
age: 29)
18-61years (median
age: 35)
0.129
% Females 50 (n = 7) 87.5 (n = 7)
Months recruited Nov-Aug Jan-Aug
Mean (±SD) photoperiod
(hrs) (Fig: 17)
13.30 (1.59) 12.27 (1.13) 0.128
Median GSE (KWh/m2) 5.10 4.41 0.258
GSE, global solar exposure; SD, standard deviation
4. 2 THE MELANOPSIN-MEDIATED POST-ILLUMINATION PUPIL
RESPONSE (PIPR)
The mean and 95% confidence limits (CL) of the pupil light reflex in response to 1 s
short wavelength (blue) and long wavelength (red) light stimuli in patients with depression
and healthy control participants are shown in Figure 13. The Figures indicate a similar mean
pupil light reflex in response to red and blue light stimuli in patients with depression and the
control group. The PIPR in response to the short wavelength blue light stimulus in the
patients with depression, however, shows a greater variability than the control group. The
mean pupil light reflex data ( 95% confidence limits) for the patients with depression and
the control participants comparing the responses from two stimuli conditions are shown in
Figure 14 and the individual data are shown in Appendix 1.0. The pupil metrics for all
outcome parameters with short and long wavelength light stimuli in patients with depression
and control participants are shown in Table 6. The baseline pupil diameter was not
significantly different between the groups (depression, 6.9 ± 1.0 mm, control, 7.2 ± 0.7 mm;
p > 0.05, independent t-test). The 6 s and the plateau PIPR amplitudes in response to blue
stimulus were not significantly different between the groups (p > 0.05, independent t-test)
(Figure 15) and therefore, only the 6 s PIPR data are reported as PIPR amplitude in the
60
further analysis. The linear regression of the PIPR amplitude in response to short wavelength
blue light stimuli as a function of age among the control participants was not significantly
different from zero, indicating that PIPR was independent of age (R2 = 0.0003, F1,11 =
0.003.92, p = 0.95;) as previously demonstrated (Adhikari et al., 2015a; Kankipati et al.,
2010). There was no correlation between the PIPR amplitude and the BDI-II scores
(Spearman r = 0.03, p = 0.90) among the patients with depression. Since the PIPR amplitude
did not differ between the groups and the sample size was small for the group comparison
with respect to season, the participants from both groups were combined to analyse the effect
of seasons. There was no significant difference in the PIPR amplitude between the
participants recruited during the summer and winter dominating months (p > 0.05,
independent t-test). The linear regression line of PIPR against photoperiod in patients with
depression and healthy controls was not significantly different from zero (R2 = 0.13, p = 0.1).
61
-1 0 0 1 0 2 0 3 0 4 0
3 0
4 0
5 0
6 0
7 0
8 0
9 0
1 0 0A
-1 0 0 1 0 2 0 3 0 4 0
B
C o n tro l µ ± 9 5 % C L
D e p re s s io n µ ± 9 5 % C L
6 s P IP R6 s P IP R
C o n tro l µ ± 9 5 % C L
D e p re s s io n µ ± 9 5 % C L
T im e (s )
Pu
pil
dia
me
ter
(% b
as
eli
ne
)
Figure 13: The pupil light reflex traces showing the mean pupil diameter with 95%
confidence limits (CL) in patients with depression (n = 8) and control participants (n =
13).
The mean pupil diameter ± 95% CL with time (s) in response to 1 s (black rectangle) long
wavelength (A) and short wavelength (B) light stimuli in patients with depression and control
group. The shaded areas and the thinner lines show the 95% CL of the mean (µ) for control
participants and patients with depression respectively. The vertical lines indicate the 6 s PIPR
amplitude.
-1 0 0 1 0 2 0 3 0 4 0
3 0
4 0
5 0
6 0
7 0
8 0
9 0
1 0 0A
Pu
pil
dia
me
ter
(% b
as
eli
ne
)
C o n tro l
R e d µ ± 9 5 % C L
B lu e µ ± 9 5 % C L
T im e (s )
6 s P IP R
-1 0 0 1 0 2 0 3 0 4 0
B
D e p re s s io n
R e d µ ± 9 5 % C L
B lu e µ ± 9 5 % C L
6 s P IP R
Figure 14: The pupil light reflex traces showing a comparison between two stimuli
conditions in patients with depression (n = 8) and control participants (n = 13).
The mean pupil diameter (µ) ± 95% confidence limits (CL) with time (s) in response to 1 s
(black rectangle) long (red) and short (blue) wavelength light stimuli in control participants
(A) and patients with depression (B). The shaded areas and thinner red lines show the 95%
CL of the mean (µ) for blue and red light stimuli respectively. The vertical lines indicate the
6 s PIPR amplitude.
62
Since there was only 1 male patient with depression and there is a known higher
prevalence of depression in females (Girgus et al., 2015), only female patients with
depression (n = 7) were compared with the females in the control group (n = 7). There was no
difference in the PIPR amplitude among females between the groups (p > 0.05, Mann-
Whitney test).
Given the known effects of SNRIs on the baseline pupil diameter and the PIPR (Bitsios
et al., 1999; Phillips et al., 2000; Siepmann et al., 2007), a separate analysis in two patients
with depression taking that drug showed no significant difference in the baseline pupil
diameter and the PIPR amplitude compared to the healthy control group (p > 0.1, Mann-
Whitney test).
Table 6: The mean and 95% CL of the PIPR and PLR metrics (% baseline) with red and blue
stimuli compared between the patients with depression and control participants
Measurements Blue stimulus Red stimulus
Depression Control Depression Control
6 s PIPR 60.31 ± 9.2 60.25 ± 6.5 94.7 ± 1.3 93.6 ± 2.4
95% CL (52.6-
68.0)
95% CL (56.4-
64.2)
95% CL (93.6-
95.8)
95% CL (92.2-
95.1)
Plateau PIPR 78 ± 12.0 79.1 ± 10.1 94.8 ± 3.6 95.7 ± 2.2
95% CL (68.0-
88.0)
95% CL (73.3-
85.0)
95% CL (91.8-
97.8)
95% CL (94.3-
97.0)
Peak PLR 46.1 ± 4.4 43.9 ± 6.1 56.9 ± 7.1 55.1 ± 5.7
95% CL (42.5-
49.8)
95% CL (40.2-
47.6)
95% CL (51.0-
62.8)
95% CL (51.7 -
58.6)
Transient PLR 23 ± 5.5 22 ± 5.2 22.4 ± 8.2 21.4 ± 5.6
95% CL (18.3-
27.5)
95% CL (19-
25.2)
95% CL (15.5-
29.3)
95% CL (18-
24.7)
Time to peak PLR 2.8 ± 0.8 2.5 ± 5.2 1.4 ± 0.2 1.5 ± 0.1
95% CL (2.2-
3.5)
95% CL (2.2-
2.8)
95% CL (1.3-
1.6)
95% CL (1.4-
1.5)
CL, confidence limit; PIPR, post-illumination pupil response; PLR, pupillary light response
63
3 0
4 0
5 0
6 0
7 0
8 0
9 0
1 0 0
6 s P IP R
A
PIP
R a
mp
litu
de
(%
ba
se
lin
e)
P la te a u P IP R
3 0
4 0
5 0
6 0
7 0
8 0
9 0
1 0 0
C o n tro l D e p re s s io n
B
C o n tro l D e p re s s io n
Figure 15: The 6 s and the plateau PIPR to short and long wavelength light stimuli in
patients with depression (n = 8) and control participants (n = 13).
The box and the whisker plots show the median, inter-quartile range and range of the 6 s
PIPR (left panel) and the plateau PIPR (right panel) in response to red and blue light stimuli.
There is no significant difference in the 6 s and plateau PIPR in response to short wavelength
(panel A) test stimuli or long wavelength control (panel B) stimuli between patients with
depression (open circles) and control participants (filled circles). Amplitudes are expressed as
percentage baseline pupil diameter.
4. 3 THE PUPIL LIGHT RESPONSE (PLR)
The peak pupil constriction amplitudes (peak PLR) and the transient PLR in response to
1 s short wavelength (blue) and long wavelength (red) light stimuli in patients with
depression and control participants are shown in Figure 16. There was no significant
difference between the groups for short wavelength (blue) (p > 0.05, independent t-test) or
long wavelength (red) stimuli (p > 0.05, independent t-test). The time to peak constriction
amplitude (Figure 17) in response to short and long wavelength light stimuli were not
significantly different between the groups (p > 0.05, independent t-test). Since there is an
64
indication that pupil constriction amplitude can be affected by SNRIs (Bitsios et al., 1999;
Phillips et al., 2000; Siepmann et al., 2007), an additional analysis was done in two patients
with depression compared to the control participants to examine whether SNRI’s had an
effect on the pupil constriction. There was no significant effect of SNRIs on the peak PLR in
response to red (p > 0.05, Mann-Whitney test) and blue (p > 0.05, Mann-Whitney test)
stimuli in the patients with depression compared to the healthy control group.
2 0
3 0
4 0
5 0
6 0
7 0
8 0
Pe
ak
PL
R (
% b
as
eli
ne
) A
B lue R ed
0
1 0
2 0
3 0
4 0
5 0
6 0
Tra
ns
ien
t P
LR
(%
ba
se
lin
e)
C o n tro l D e p re s s io n
B
C o n tro l D e p re s s io n
Figure 16: The peak pupil constriction (peak PLR) and the transient PLR amplitudes to
short and long wavelength light stimuli in patients with depression (n = 8) and control
participants (n = 13).
The box and the whisker plots show the median, inter-quartile range and range of the peak
PLR (A) and the transient PLR (B) in response to short wavelength blue (left panel) and long
wavelength red (right panel) stimuli in patients with depression and healthy controls
measured during 1 s light stimuli. Amplitudes plotted as percentage baseline pupil diameter
for the patients with depression (open circles) and control participants (filled circles) show no
significant differences between the groups.
65
0
1
2
3
4
5T
ime
to
pe
ak
PL
R (
s)
C o n tro l D e p re s s io n
A
C o n tro l D e p re s s io n
B
Figure 17: The time to peak pupil constriction amplitude (time to peak PLR) to short
and long wavelength light stimuli in patients with depression (n = 8) and control
participants (n = 13).
The box and the whisker plots showing the median, inter -quartile range and range of the time
to peak PLR amplitude in response to 1 s short wavelength blue (A) and long wavelength red
(B) stimuli in patients with depression and healthy controls indicates no significant difference
between the groups.
4. 4 CONTRAST SENSITIVITY (CS)
The photopic log contrast sensitivity scores are shown in Figure 18. The log CS were
not different between the groups (depression, 1.83 ± 0.1, control, 1.76 ± 0.1, p > 0.05,
independent t-test). The linear regression line of BDI-II scores in the patients with depression
as a function of log CS was not significantly different from zero (R2 = 0.16; F1, 6 = 01.22; p =
0.31) indicating that depression severity is not associated with contrast sensitivity in this
sample of participants.
66
C o ntro l D e p re s s io n
1 .6
1 .7
1 .8
1 .9
2 .0L
og
CS
Figure 18: Contrast sensitivity in patients with depression and control participants.
Photopic log contrast sensitivity (CS) measured with the Pelli-Robson chart in patients with
depression (open circles) and control participants (filled circles) showing no significant
difference in log contrast sensitivity between the groups. The box and the whisker plots
indicate median, inter-quartile range and range.
4. 5 LIGHT EXPOSURE
Daily average daylight exposure, nightlight exposure and sleep parameters (sleep
length, sleep efficiency and sleep onset latency) in patients with depression and control group
are shown in Table 7. The patients with depression and control participants went to bed at
similar clock times (~ 23:00 hrs) with the mean time to bed in the patients with depression
and control participants being 22:59 hrs and 23:16 hrs, respectively. Similarly, the patients
with depression did not have different times to wake than the control participants with mean
wake up times in the patients with depression and control participants being 7:36 hrs and 7:37
hrs, respectively. Hence, their sleep lengths (p > 0.05, Mann-Whitney test) and mid-sleep
times (p > 0.5, independent t-test) were not significantly different. The sleep efficiency was
not significantly different between the groups (p > 0.05, Mann-Whitney test). The sleep onset
67
latency was, however, significantly longer for the patients with depression than the control
participants (p < 0.05, independent t-test). There was no significant correlation between the
PIPR amplitude and the sleep length (Spearman r = -0.3, p = 0.42), sleep efficiency
(Spearman r = 0.26, p = 0.53) and sleep onset latency (Spearman r = -0.21, p = 0.61) among
the patients with depression.
Table 7: The light exposure and sleep profile compared between the patients with depression
and healthy control participants.
Depression (n = 8) Control (n = 14) P value
Mean (SD) daylight (lux) 831 (391)
95% CI (666-1229)
947 (488)
95% CI (504-1158)
0.57
Median nightlight (lux) 24.5 15 0.76
Median sleep length (hrs) 8.6 8.1 0.65
Median sleep efficiency (%) 61 65 0.33
Mean (SD) sleep onset latency (mins) 20.8 (19.7) 9.1 (3.5) 0.03*
*p < 0.05; SD, standard deviation; CI, confidence interval
There was no significant effect of the season and time of the day in light exposure
levels between the groups (p = 0.95, factorial univariate ANOVA). The combined mean daily
light exposure levels among the patients with depression and healthy control participants
were not significantly different between the winter (806 ± 508 lux) and summer (973 ± 410
lux) (p > 0.1, independent t-test) months. There was no significant correlation between the
GSE and the mean daylight exposure experienced by the patients with depression (Pearson r
= 0.40, p = 0.32) and the control participants (Pearson r = 0.27, p = 0.36).
Daily clock hours light exposure starting and ending at 0:00 hrs and the circadian hours
light exposure starting with the wake time in patients with depression and healthy control
participants are shown in Figures 19 (A) and 19 (B) respectively. The Figures show the group
data (depression; n = 8 and control; n = 14) on a logarithmic lux scale and the symbols show
the mean and standard deviation.
68
1
1 0
1 0 0
1 0 0 0
1 0 0 0 0
1 0 0 0 0 0
C o n tro l
D e p re s s io n
T im e (H H :M M )
0 :0 0 4 :0 0 8 :0 0 1 2 :0 0 1 6 :0 0 2 0 :0 0 2 3 :0 0
S LE E P (C ontro l)
S L E E P (D e p re s s io n )
D a y L ig h t co n tro l
D a y L ig h t D e p re s s io n
T w ilig h t (s c o to p ic + M e s o p ic )
O ff ic e (p h o to p ic )
O v e rc a s t d a y /s h o p p in g c e n tre s (p h o to p ic )
F u ll D a y L ig h t (p h o to p ic )
D a rk O u td o o r/In d o o r A re a s
(m e s o p ic + P h o to p ic )
AL
ux
1
1 0
1 0 0
1 0 0 0
1 0 0 0 0
1 0 0 0 0 0
C o n tro l
D e p re s s io n
A fte r-w a k e h o u rs
D a y L ig h t D e p re s s io n
D a y L ig h t c o n tro l
O ff ic e (P h o to p ic )
O v e rc a s t d a y /s h o p p in g c e n tre s (P h o to p ic )
F u ll D a y L ig h t (p h o to p ic )
T w ilig h t (s c o to p ic + M e s o p ic )
S LE E P (C ontro l)
7 :3 7 1 5 :3 7 2 3 :3 7 6 :3 7
7 :3 6 1 5 :3 6 2 3 :3 6 6 :3 6
W a k e T im eS le e p (D e p re s s io n )
B
Lu
x
D a rk O u td o o r/In d o o r A re a s
(m e s o p ic + P h o to p ic )
0 2 4 6 8 10 12 14 16 18 20 22
Figure 19: Daily mean (±SD) clock hours (A) and circadian hours (B) light exposure
presented in logarithmic lux scales in patients with depression and healthy participants.
Light blue circles (mean ± SD) show the light exposure in the control participants. Dark blue
squares (mean ± SD) show the light exposure in patients with depression. The illuminance
(lux) data are expressed on a logarithmic lux scale (log10). Duration of daylight and sleep in
patients with depression and control participants are shown in the upper panel (A). Actual
clock hours and sleep duration in patients with depression and control participants are shown
in the lower panel (B). Scales on the right (A and B) show the typical conditions at which
specific light exposure levels are experienced. Individuals in both groups experience similar
light levels most of the time during the day.
69
The mean daylight exposure in the patients with depression was not significantly
different from that of the control participants (p > 0.05, independent t-test) (Table 7). The
control participants and the patients with depression experienced similar light exposure of ~
2.9 log lux immediately after waking up. After an hour and a half of wake time (9:00 hrs), the
control participants experienced a peak light exposure of 3.1 log lux which then plateaued
at ~ 3 log lux for the next 3 hours (10:00 hrs – 13:00 Hrs). Light exposure in the patients with
depression showed a gradual increase to a peak level of ~ 3 log lux after 6 hours of wake time
(15:00 hrs). The light exposure levels at clock hours when light levels peaked for both groups
(9:00 hrs for control participants and 15:00 hrs for patients with depression) did not differ
significantly (p > 0.05, factorial univariate ANOVA). During the day, both groups were
exposed to the photopic illumination equivalent to that on an overcast day for at least 8 hours
after wake time (8:00 to 16:00 clock hours). Both groups experienced light levels equivalent
to an office light exposure (photopic) between 16:00 to 18:00 clock hours. During the night
hours, both groups were exposed to scotopic and mesopic ranges and the median nightlight
exposure between the groups was not significantly different (p > 0.05, Mann-Whitney test)
(Table 7). Despite different daylight trends between the groups, the light levels as a function
of clock hours were not significantly different between the groups (p = 0.90, factorial
univariate ANOVA).
The daily mean number of minutes of light exposure experienced by both groups to
three common illuminance ranges (≥ 10,000 lux, ≥ 5000 lux and ≥ 2500 lux) recommended
for light therapy in depression is shown in Figure 20. The patients with depression were
exposed to a light level ≥ 10,000 lux for a mean duration of 21 ± 9 (95% CL: 14-29) min
daily which was not significantly different (p = 0.6, independent t-test) than the mean
minutes exposed to ≥ 10,000 lux by the control group (24.6 ± 15 min; 95% CL: 16-33.4). The
mean duration of daily light exposure in the patients with depression was 36 ± 25.5 (CL: 15-
70
57.5) min and 47 ± 37.4 (95% CL: 16-78.5) min daily to exposure levels of ≥ 5000 lux and ≥
2500 lux, respectively. Control participants were exposed daily to the light exposure levels ≥
5000 lux and ≥ 2500 lux for 40 ± 29 (95% CL: 23-56.5) min and 57.7 ± 44 (95% CL: 32.3-
83) min respectively. The exposure duration between the groups was not significantly
different for light levels ≥ 5000 lux (p = 0.76, independent t-test) and ≥ 2500 lux (p = 0.58,
independent t-test). The median group light exposure duration (min) was less than the
recommended duration (Even et al., 2008; Gallin et al., 1995; Glickman et al., 2006;
Haffmans et al., 2008; Kräuchi et al., 1990; Meesters et al., 2011; Naus et al., 2013; Szabó et
al., 2004; Winkler et al., 2005; Wirz-Justice et al., 1999) at ≥ 10,000 lux (30 min), ≥ 5000 lux
(60 min) or ≥ 2500 lux (120 min).
0
3 0
6 0
9 0
1 2 0
1 5 0
Du
rati
on
(m
ins
)
C o n tro l
D e p re s s io n
1 0 ,0 0 0 5 0 0 0 2 5 0 0
Lux
Figure 20: Daily duration of exposure to the illuminance levels ≥ 10000 lux, ≥ 5000 lux
and ≥ 2500 lux in patients with depression and control participants.
The box and the whisker plots show the median, inter-quartile range and range of the duration
(min) spent to light levels ≥ 10,000 lux, ≥ 5000 lux and ≥ 2500 lux by patients with
depression and control participants. The filled circles and open circles represent cumulative
minutes to light exposure levels shown under x-axis spent by the control participants and
patients with depression respectively. The blue horizontal lines represent the recommended
treatment duration with specific light levels showing none of the groups on average spent
recommended time daily.
71
CHAPTER 5: DISCUSSION, CONCLUSIONS AND FUTURE
DIRECTIONS
This study examined the role of ipRGCs, the primary cells in the visual system to
encode ambient environmental light and the relationship of ipRGC function to daily light
exposure in patients with non-seasonal depressive disorder. There were no differences in the
ipRGC mediated post-illumination pupil response (PIPR) amplitude measured with a
Maxwellian view open-loop pupillometer under a high melanopsin excitation condition
among people with non-seasonal depression and healthy controls (Figure 15). This study did
not observe any difference in daily ambient light exposure between the patients with non-
seasonal depression and healthy individuals (Figure 19). Moreover, the PIPR amplitude was
not related to the seasonal change in light exposure levels. The peak PLR, the transient PLR
and the time to peak PLR amplitudes in response to the short duration, high intensity, short
and long wavelength light stimuli (Figure 16 and 17) and photopic contrast sensitivity (Figure
18) were not significantly different between the groups. Taken together, in this participant
sample, there is no relationship between ambient light exposure and inner retinal (ipRGC) or
outer retinal (rod and cone) functions in patients with non-seasonal depression.
While the hypothesis of a reduced PIPR in patients with non-seasonal depression could
not be confirmed, the findings of a normal PIPR, transient PLR and peak pupil constriction
amplitudes are supported by a recent study in MDD that included patients with non-seasonal
depression (n = 12) and SAD (n = 7) using a Newtonian view pupillometer (Laurenzo et al.,
2016) and stimulus conditions that were optimised to the maximum melanopsin excitation (1
s stimulus, irradiance ~ 14.8 log quanta.cm-2.s-1) (Adhikari et al., 2015b). A previous study in
patients with SAD, however, detected a significant reduction in the melanopsin-mediated
PIPR amplitude (Roecklein et al., 2013) despite using 30 s stimuli with lower retinal
irradiance (12.3 log quanta.cm-2.s-1) and under closed-loop conditions. While an open-loop
72
pupillometer under high melanopsin excitation conditions as used in the present study may
have further increased the PIPR amplitude difference (Adhikari et al., 2015b) in the SAD
study (Roecklein et al., 2013), the current study’s finding also supports different underlying
pathomechanisms between the patients with non-seasonal depression and SAD.
Treatment with short wavelength (blue) light is an established therapy in MDD
(Glickman et al., 2006; Lieverse et al., 2011; Meesters et al., 2011; Royer et al., 2012), yet
the mechanism of action is poorly understood. It was hypothesised in the current study that
the hourly ambient light exposure and the duration spent under light exposure levels
recommended for depression treatment would be lower and shorter, respectively in the
patients with non-seasonal depression compared to the healthy control participants reflecting
the basis of the positive effect of light therapy. This study is the first indicating that the daily
hourly light exposure levels and the duration spent in bright illumination commonly
recommended for depression light therapy do not differ between the two groups. None of the
groups spent the recommended treatment duration of 30 min, 60 min and 120 min under light
exposure of ≥ 10,000, ≥ 5000 and ≥ 2500 lux, respectively. This is supported by previous
studies in SAD that also demonstrate similar light exposure levels (Graw et al., 1999; Oren et
al., 1994) and the duration spent under bright light (> 1000 lux) (Guillemette et al., 1998)
between patients with SAD and healthy individuals. Laurenzo et al. (2016) evaluated the
light exposure levels within the MDD patients only and did not compare them with a control
group, but showed a significant positive relationship of light exposure levels with the PIPR
and the transient PLR in response to a high-intensity blue light stimulus. These findings,
however, need to be confirmed by including a control group. The current study did not show
a relationship between light exposure and PIPR in both MDD and control groups, possibly
due to the different geographical locations of light exposure measurement between the two
studies. Laurenzo et al’s. (2016) study was done in Iowa City, USA in the northern
73
hemisphere where temperatures range between 32°C to -28°C with participants’ individual
light exposure levels on average, ranging from 2,255 lux in summer to 207 lux in winter
(Laurenzo et al., 2016). Since, seasonal changes in light exposure have been shown to affect
the PIPR in normal individuals (Münch et al., 2016), lower PIPR associated with lower light
exposure is therefore expected in MDD patients (Laurenzo et al., 2016). The current study
was conducted in Brisbane, Australia, a city in the southern hemisphere, with a sub-tropical
climate and the study measured similar light exposure levels in the summer and winter
months. Although the global solar exposure (GSE) during the summer dominating months
was significantly higher than that during the winter dominating months, the light exposure
levels between groups with respect to the seasons and the time of the day were not
significantly different. Moreover, the GSE measured over the study city (Brisbane) during
the study recruitment days were not different between the groups. In addition, the daily
average light exposure in both groups did not change with the GSE over the recruitment
period, indicating that the season had no effect in light exposure experienced by the study
participants, most likely due to the distribution of participants in both groups in the current
study through all seasons.
The PIPR amplitude in response to blue light stimuli is consistent with a previous research
that investigated individuals with healthy eyes without depression (Adhikari et al., 2016b)
using similar stimulus and pupillometry paradigms. The PIPR in response to blue light shows
a greater variation than to red light. The variation is consistent with previous studies that used
similar stimulus paradigms as current study (Adhikari et al., 2016b; Maynard et al., 2015).
The exact biological mechanism is, however, unknown. The variation may have arisen due to
difference in the density of ipRGC among human retinae (Dacey et al., 2005; Jusuf et al.,
2007; Liao et al., 2016). The peak PLR (percentage baseline amplitude) in response to red
light stimuli, however, was slightly higher (5%) compared to that reported by Adhikari et al.
74
(2016b) and this may have occurred due to inter-observer variability. A higher variability in
the PLR and PIPR amplitudes in the depression group than the control group was seen in the
present study consistent with a previous study (Laurenzo et al., 2016). The variation may
have arisen due to different biological mechanisms involved in different sub-types of non-
seasonal depression and the medications used for the treatment. The small sample size of the
studies may further have contributed to the variations, although the study populations are
comparable with the pupil study in SAD (Roecklein et al., 2013). The PIPR amplitude among
SAD patients did not show a variation compared to the healthy controls (Roecklein et al.,
2013) and may reflect the homogeneity of this group’s condition, hence the same biological
mechanisms among the patients with SAD.
The PIPR in response to a short wavelength light stimulus is predominantly controlled
by the OPN projecting M1 ipRGC sub-type which also projects to the mood centres indirectly
via the SCN in a mouse model (Baver et al., 2008). Depression caused by aberrant light
exposure is mediated through ipRGC pathway affecting mood, but not the circadian rhythm
in mice, suggesting a direct mood pathway independent of the SCN (Legates et al., 2012).
However, based on the results of this study that does not show a relationship between the
melanopsin-mediated PIPR and non-seasonal depression, it is likely that diurnal humans have
a normal ipRGC function in non-seasonal depression compared to the nocturnal mice or
perhaps that mood regulation in non-seasonal depression is driven via other ipRGC sub-types
that project directly to the mood centres, but not to the SCN or OPN. While a study in mice
demonstrated that M1 ipRGCs have a direct projection to the SCN and multiple brain nuclei,
including the OPN, the ventral medial hypothalamus (VMH), the intergeniculate leaflet
(IGL), the ventral lateral geniculate nucleus (vLGN), the superior colliculus (SC), and peri-
habenular nucleus (pHb) (Fernandez et al., 2016) that have roles in mood, circadian rhythm,
sleep functions (Gooley et al., 2003; Harrington, 1997; Hattar et al., 2006; Miller,
75
Obermeyer, Behan, & Benca, 1998) and reward (Matsumoto and Hikosaka, 2007), human
studies are yet to confirm similar projections of the M1 subtype to the multiple brain areas.
The projections of M1 ipRGCs to the SCN in mice are greater than those in other brain areas
(Fernandez et al., 2016) which indicates that M1 ipRGCs have a more prominent role in the
circadian photoentrainment than in other behavioural functions such as mood. There is also
evidence that in mice, Brn3b-positive M1 ipRGCs that project to the OPN to control pupil
light reflex, do not project to the SCN to drive circadian photoentrainment (Chen et al., 2011)
suggesting two separate pathways. The differentiation of ipRGC based on Brn3b expression
has not been shown in humans yet, but SAD is likely to be driven by the same M1 ipRGC
projecting to the OPN and SCN hence affects both, pupil response and circadian rhythm in
humans. Indeed, SAD is associated with a short photoperiod and prolonged melatonin
production in winter (Lewy et al., 1987; Wehr et al., 2001) and depression treatment with
morning light therapy in SAD is brought about by advancing the circadian phase (Burgess et
al., 2004).
Importantly, in this sample, the light exposure levels in both groups were within the
melanopsin activation range (photopic and high mesopic illumination) (Dacey et al., 2005)
between the wake and sleep times throughout the day and so there would be a normal
melanopsin signaling for the photoentrainment. Although the light exposure trends were
different between the groups, both groups, on average, spent most of the time during a day,
equivalent to the outdoor light levels an individual would experience during an overcast day.
The evening light exposure in both groups was within the range of indoor office photopic
light levels. The light exposure during night hours before sleep was within the photopic and
mesopic ranges in both groups. The light exposure levels in the study participants were also
not affected by their photoperiod or sleep lengths. The daily photoperiods and sleep lengths
between the patients with depression and healthy control participants were not significantly
76
different. Individuals in both groups had similar wake times and received the last light at
similar times. Hence, the apparent photoperiods (wake time to time of last light) were similar.
The subjective sleep onset latency was significantly longer in the depression group, which is
consistent with a previous study (Lovato & Gradisar, 2014). The Actigraphy-derived sleep
efficiency and sleep lengths were not different between the groups. Depression is, however,
thought to be accompanied by sleep and circadian rhythm abnormalities (Argyropoulos et al.,
2005; Borbély et al., 1982; Lovato et al., 2014; Wirz-Justice, 2006). Normal sleep efficiency
and sleep length found in this study could be confounded by the medication used by the
patients with depression (Appelboom-Fondu, Kerkhofs, & Mendlewicz, 1988; Lemoine,
Guilleminault, & Alvarez, 2007). The sleep onset latency, however, did not correlate
significantly with the PIPR amplitude indicating that there was no interaction between the
melanopsin function and sleep onset latency in non-seasonal depression.
The visual function measured as log contrast sensitivity (CS) was not different between
the groups. While a previous study (Wesner et al., 2006) measured the CS to Gabor targets of
various spatial and temporal frequencies in patients with seasonal and non-seasonal
depression with normal vision and observed an increased CS, more recent studies with
different methodologies and larger sample sizes showed a reduced contrast sensitivity in
patients with non-seasonal depression (Bubl et al., 2009; Fam et al., 2013). Retinal
dopaminergic dysregulation has been hypothesised to affect the visual contrast sensitivity in
patients with non-seasonal depression (Bubl et al., 2009; Fam et al., 2013). No study has,
however, reported a direct measure of retinal dopamine in depression. M1 ipRGCs are
believed to modulate cone adaptation via their retrograde axonal collaterals to the inner
plexiform layer (IPL) where they synapse with the dopaminergic amacrine cells (Joo et al.,
2013). Visual functions are partially controlled by retrograde signaling of ipRGCs to the
outer retinal photoreceptors via the dopaminergic system in the retina (Prigge et al., 2016).
77
This study showing normal ipRGC function and visual contrast sensitivity suggests a normal
dopaminergic neurotransmission within the retina in non-seasonal depression. This
assumption needs to be, however, interpreted with caution as common antidepressant
medications (e.g. SSRIs) may decrease the central dopaminergic activity (Esposito, 2006).
In summary, this study observed a normal melanopsin function and light exposure in
non-seasonal depression patients residing in Brisbane, Australia. In non-seasonal depression,
diurnal humans, possibly have a robust ipRGC function compared to the nocturnal animal
models that show depressive behaviour in response to aberrant light (Legates et al., 2012) or
mood disorder in non-seasonal depression in humans is modulated by other sub-types of
ipRGCs that were not measured in this study. It is, however, well recognised that depression
is a multifactorial condition (Goldberg, 2006) and it is likely that higher brain centres play a
role in the pathophysiological processes independently of ipRGC function and ambient light
exposure and these relationships require further exploration.
5. 1 LIMITATIONS
The study suggests similar mean PIPR amplitude between the groups, indicating that
there is no effect of non-seasonal depression on the melanopsin function. The result of the
study may have been underpowered due to the small sample size that estimated 45 samples
per group based on the mean and standard deviation of the samples from the previous SAD
study (Roecklein et al., 2013). The patient number was limited by the nature of the disease
and recruitment difficulties. The sample size of this study is, however, comparable to the two
other studies that evaluated the melanopsin function in patients with depression (Laurenzo et
al., 2016; Roecklein et al., 2013); Roecklein et al. (2013) investigated 15 patients with SAD
and Laurenzo et al. (2016) evaluated 12 patients non-seasonal depression. The sample size of
78
the current study is also comparable to previous studies investigating light exposure in 11
(Guillemette et al., 1998) and 13 (Oren et al., 1994) patients with SAD.
Antidepressants (SNRIs and SSRIs) are known to affect the autonomic nervous system
(Richelson, 1994), hence influence the resting pupil diameter and pupillary responses (Bär,
Greiner, Jochum, Friedrich, Wagner, & Sauer, 2004; Bitsios et al., 1999; Phillips et al.,
2000). There is evidence that the SNRI class of antidepressants affects the baseline pupil
diameter, pupil constriction amplitude and pupil recovery time after light offset (Bitsios et al.,
1999; Phillips et al., 2000; Siepmann et al., 2007). The present study had two patients with
depression taking SNRIs. The pupil responses of those taking and not taking SNRIs were,
however, not different than that of the healthy controls, indicating no effect of SNRIs on the
patient’s pupil data. The effect of SSRI on the baseline pupil diameter is described
inconsistently (Bitsios et al., 1999; Phillips et al., 2000; Schmitt et al., 2002) showing no
change (Bitsios et al., 1999; Phillips et al., 2000) or an increased pupil diameter (Schmitt et
al., 2002) in individuals using SSRIs. Seven patients in the depression group were taking
SSRIs, however, there was no significant difference in baseline pupil diameter in the patients
taking SSRIs compared to the healthy controls. To account for the baseline pupil differences
that might have occurred due to the use of the medications, the PLR and PIPR data of the
participants in both groups were normalized to their individual baselines as percentage
baseline amplitudes.
Three participants in this study had recurrent depressive episodes with the maximum
number of episodes being two and the minimum duration of onset being two years. Although
these patients scored higher than cutoff on the atypical HDRS-SAD scale, a diagnosis of
winter SAD could not be made as the peak depressive symptoms during winter with
remission during the summer was not confirmed. Studies suggest inconsistencies with the
HDRS scale (Uher, Farmer, Maier, Rietschel, Hauser, Marusic, Mors, Elkin, Williamson,
79
Schmael, Henigsberg, Perez, Mendlewicz, Janzing, Zobel, Skibinska, Kozel, Stamp, Bajs,
Placentino, Barreto, McGuffin, & Aitchison, 2008) and inter-rater discrepancies with HDRS-
SAD with respect to the atypical SAD mood symptoms like “fatigability” and ‘hypersomnia”
(Rohan et al., 2016). It is unlikely that SAD participants have been included in this study as
none of the participants had a self-reported history of SAD with worst mood during winter
and complete remission during summer.
Light exposure data should be interpreted with caution as an accurate measurement of
light exposure by an ambulatory light sensor may be limited by the performance of the device
(Cao et al., 2015b). While a Daysimeter is a device that has a light sensor at eye level
(Smolders et al., 2013), the Actiwatch-L (Philips Respironics, Eindhoven, Netherlands) has
been validated against the Daysimeter (Rensselaer Polytechnic Institute, Troy, NY) in
patients after cardiac surgery showing that the Actiwatch-L underestimates eye level light
exposure by < 10 lux at light levels < 5000 lux (Jardim, Pawley, Cheeseman, Guesgen,
Steele, & Warman, 2011); the difference increases with increase in light exposure at eye
level. The spectral output from the Actiwatch used under direct exposure to sunlight also
underestimate the actual light level (Cao et al., 2015b). Cao et al., 2015 suggests that the red-
green-blue (RGB) spectral Actiwatch underestimates 0.123-0.230 log units for long
wavelength light (red) and 0.145 log units for short wavelength light (blue) than the actual
level, whereas the light estimates for medium wavelength (green) are more accurate. The
light level estimation by the light sensors in an ambulatory device is suggested to also vary
with the ambient temperature (Cole, Kripke, Wisbey, Mason, Gruen, Hauri, & Juarez, 1995).
This study was aimed to compare the ambient light exposure levels between two groups, and
both groups used the same devices. Hence, any differences in the light measurements within
the groups would not affect the actual difference between the groups. Further, this study did
80
not have control over ambient indoor temperatures, although the outdoor global solar
exposure (GSE) was not different between the participants.
Estimation of the nightlight exposure levels during sleep may be affected by sleep
disturbance among the participants and the light sensors being covered by the clothes. It is,
however, unlikely that nightlight data were affected by sleep disturbance as sleep efficiency
between the groups was not significantly different. Nonetheless, the nightlight exposure
during sleep may be of less relevance to the image and non-image-forming functions as a
person's eyes are closed during sleep.
5. 2 CONCLUSION AND FUTURE DIRECTIONS
This thesis addressed an important question of ambient light exposure and its
relationship with the non-image forming (ipRGCs) functions in non-seasonal depression.
An ambulatory Actigraphy device was used to measure the ambient light exposure
levels and a custom built Maxwellian view open-loop pupillometer with previously optimised
stimulus paradigms (Adhikari et al., 2015b) was used to compare the inner retinal ( ipRGC)
and outer retinal (rod-cone) function by measuring the PIPR and PLR amplitudes in response
to red and blue light stimuli in patients with depression and healthy control participants. The
daily hourly light exposure levels and duration spent to bright illumination daily did not show
a relationship with non-seasonal depression. No relationship of light exposure to the inner
retinal melanopsin and outer retinal rod and cone functions in non-seasonal depression was
shown by the study. This finding expands previous knowledge in depressive disorders.
Depression is a multi-factorial condition and this study suggests, while M1 ipRGCs that
project to the OPN and the SCN are dysfunctional in SAD (Roecklein et al., 2013), they are
not dysfunctional in non-seasonal depression. The lack of a significant correlation between
81
the melanopsin-mediated PIPR and circadian parameters (sleep length, sleep efficiency and
sleep latency) in the current study provides further evidence to this conclusion. Projections of
M1 ipRGC to multiple brain targets in animal models have been confirmed (Fernandez et al.,
2016). There is, however, limited knowledge of M1 ipRGC projections to the mood centres
in humans. Future studies should focus on human research into ipRGC sub-types and their
projections to the brain nuclei. Studies may be initiated in primates (e.g., macaque) that
resemble humans in many aspects.
A normal melanopsin function and light exposure levels in non-seasonal depression
patients indicate that improvement in depression symptoms with light therapy is independent
of the ambient light exposure. While there is a relationship between light exposure and
depression (Ashkenazy-Frolinger et al., 2010; Ashkenazy et al., 2009; Bedrosian et al., 2011;
Fonken et al., 2009; Fonken et al., 2012; Fujioka et al., 2011; Legates et al., 2012; Workman
et al., 2011) and an association between ipRGC and non-seasonal depression has been clearly
established in animal models (Legates et al., 2012), such experiments with controlled light
exposure have not been conducted in humans for ethical reasons. Future research in humans
with and without ipRGC dysfunction for instance, due to retinal disease (Adhikari et al.,
2016b; Feigl et al., 2011; Feigl et al., 2014; Kankipati et al., 2011; Kardon, Anderson,
Damarjian, Grace, Stone, & Kawasaki, 2011; Kelbsch et al., 2016; Markwell et al., 2010;
Maynard et al., 2015; Obara, Hannibal, Heegaard, & Fahrenkrug, 2016) can be done to
understand the effect of light on mood and behaviour with respect to the changes in light
exposure characteristics like wavelength, intensity, duration of light-dark cycle and their
effects on the melatonin profile.
Moreover, light exposure is subject to high variation as it is influenced by season,
geography, the individual’s occupation, indoor artificial lighting and sleep-wake habits (Cole
et al., 1995; Gou et al., 2015; Savides, Messin, Senger, & Kripke, 1986; Shochat, Martin,
82
Marler, & Ancoli-Israel, 2000; Smolders et al., 2013; Thorne, Jones, Peters, Archer, & Dijk,
2009). Future research on light exposure with respect to the season, occupation and lifestyle
in population with depression is required. Daily logs of the type of artificial light and duration
of the exposure to artificial lights can be incorporated to understand the difference in natural
and artificial light exposure. Since the light sensors in ambulatory devices may over- or
under-estimate light (Cao et al., 2015b; Jardim et al., 2011), future studies could use light
sensors at eye level (Daysimeter) to give a more accurate estimation of daily ocular light
exposure (Jardim et al., 2011; Smolders et al., 2013).
83
REFERENCES
Adhikari, P., Feigl, B., & Zele, A. J. (2016a). Rhodopsin and melanopsin contributions to the
early redilation phase of the post-illumination pupil response (PIPR). PloS One, 11(8),
e0161175.
Adhikari, P., Pearson, C. A., Anderson, A. M., Zele, A. J., & Feigl, B. (2015a). Effect of age
and refractive error on the melanopsin mediated post-illumination pupil response
(PIPR). Scientific Reports, 5.
Adhikari, P., Zele, A. J., & Feigl, B. (2015b). The post-illumination pupil response (PIPR).
Investigative Ophthalmology and Visual Science, 56(6), 3838-3849.
Adhikari, P., Zele, A. J., Thomas, R., & Feigl, B. (2016b). Quadrant field pupillometry
detects melanopsin dysfunction in glaucoma suspects and early glaucoma. Scientific
Reports of the Istituto Superiore di Sanita, 6, 33373.
Agorastos, A. M. D., Skevas, C. M. D., Matthaei, M. M. D., Otte, C. M. D., Klemm, M. M.
D., Richard, G. M. D., & Huber, C. G. M. D. (2013). Depression, anxiety, and
disturbed sleep in glaucoma. The Journal of Neuropsychiatry and Clinical
Neurosciences, 25(3), 205-213.
Ancoli-Israel, S., Cole, R., Alessi, C., Chambers, M., Moorcroft, W., & Pollak, C. (2003).
The role of actigraphy in the study of sleep and circadian rhythms. American
Academy of Sleep Medicine Review Paper. Sleep, 26(3), 342-392.
Appelboom-Fondu, J., Kerkhofs, M., & Mendlewicz, J. (1988). Depression in adolescents
and young adults — polysomnographic and neuroendocrine aspects. Journal of
Affective Disorders, 14(1), 35-40.
Arendt, J. (1989). Melatonin: A new probe in psychiatric investigation? The British Journal
of Psychiatry, 155, 585-590.
Argyropoulos, S. V., & Wilson, S. J. (2005). Sleep disturbances in depression and the effects
of antidepressants. International Review of Psychiatry, 17(4), 237-245.
Åsberg, M., & Germanis, M. (1972). Ophthalmological effects of nortriptyline–relationship
to plasma level. Pharmacology, 7(5-6), 349-356.
Ashkenazy-Frolinger, T., Kronfeld-Schor, N., Juetten, J., & Einat, H. (2010). It is darkness
and not light: depression-like behaviors of diurnal unstriped Nile grass rats
maintained under a short photoperiod schedule. Journal of Neuroscience Methods,
186(2), 165-170.
Ashkenazy, T., Einat, H., & Kronfeld-Schor, N. (2009). We are in the dark here: induction of
depression-and anxiety-like behaviours in the diurnal fat sand rat, by short daylight or
melatonin injections. International Journal of Neuropsychopharmacology, 12(1), 83-
93.
Australian Government, B. O. M. (2016). Daily global solar exposure, Brisbane Retrieved 15
August, 2015, from
http://www.bom.gov.au/jsp/ncc/cdio/weatherData/av?p_nccObsCode=193&p_display
_type=dailyDataFile&p_startYear=&p_c=&p_stn_num=040913
Bao, A. M., Meynen, G., & Swaab, D. F. (2008). The stress system in depression and
neurodegeneration: Focus on the human hypothalamus. Brain Research Reviews,
57(2), 531-553.
Bär, K.-J., Greiner, W., Jochum, T., Friedrich, M., Wagner, G., & Sauer, H. (2004). The
influence of major depression and its treatment on heart rate variability and pupillary
light reflex parameters. Journal of Affective Disorders, 82(2), 245-252.
Barrionuevo, P. A., Nicandro, N., McAnany, J. J., Zele, A. J., Gamlin, P., & Cao, D. (2014).
Assessing rod, cone, and melanopsin contributions to human pupil flicker responses.
Investigative Ophthalmology and Visual Science, 55(2), 719-727.
84
Baver, S. B., Pickard, G. E., Sollars, P. J., & Pickard, G. E. (2008). Two types of melanopsin
retinal ganglion cell differentially innervate the hypothalamic suprachiasmatic nucleus
and the olivary pretectal nucleus. European Journal of Neuroscience, 27(7), 1763-
1770.
Bayer, H. M., & Glimcher, P. W. (2005). Midbrain dopamine neurons encode a quantitative
reward prediction error signal. Neuron, 47(1), 129-141.
Beauchemin, K., & Hays, P. (1997). Phototherapy is a useful adjunct in the treatment of
depressed in‐patients. Acta Psychiatrica Scandinavica, 95(5), 424-427.
Beck, A. T., Steer, R. A., Ball, R., & Ranieri, W. (1996). Comparison of Beck Depression
Inventories -IA and -II in psychiatric outpatients. Journal of Personality Assessment,
67(3), 588-597.
Bedrosian, T. A., Fonken, L. K., Walton, J. C., Haim, A., & Nelson, R. J. (2011). Dim light at
night provokes depression-like behaviors and reduces CA1 dendritic spine density in
female hamsters. Psychoneuroendocrinology, 36(7), 1062-1069.
Belenky, M. A., Smeraski, C. A., Provencio, I., Sollars, P. J., & Pickard, G. E. (2003).
Melanopsin retinal ganglion cells receive bipolar and amacrine cell synapses. Journal
of Comparative Neurology, 460(3), 380-393.
Bergamin, O., & Kardon, R. H. (2003). Latency of the Pupil Light Reflex: Sample Rate,
Stimulus Intensity, and Variation in Normal Subjects. Investigative Ophthalmology
and Visual Science, 44(4), 1546-1554.
Berson, D. M., Castrucci, A. M., & Provencio, I. (2010). Morphology and mosaics of
melanopsin-expressing retinal ganglion cell types in mice. The Journal of
Comparative Neurology, 518(13), 2405-2422.
Berson, D. M., Dunn, F. A., & Takao, M. (2002). Phototransduction by retinal ganglion cells
that set the circadian clock. Science, 295(5557), 1070-1073.
Bitsios, P., Szabadi, E., & Bradshaw, C. M. (1999). Comparison of the effects of venlafaxine,
paroxetine and desipramine on the pupillary light reflex in man.
Psychopharmacology, 143(3), 286-292.
Bodis-Wollner, I., Marx, M. S., Mitra, S., Bobak, P., Mylin, L., & Yahr, M. (1987). Visual
dysfunction in Parkinson's disease. Brain, 110(6), 1675-1698.
Borbély, A., & Wirz-Justice, A. (1982). Sleep, sleep deprivation and depression. Human
Neurobiology, 1(205), 10.
Bradley, M. M., Miccoli, L., Escrig, M. A., & Lang, P. J. (2008). The pupil as a measure of
emotional arousal and autonomic activation. Psychophysiology, 45(4), 602-607.
Brainard, G. C., Hanifin, J. P., Greeson, J. M., Byrne, B., Glickman, G., Gerner, E., & Rollag,
M. D. (2001). Action spectrum for melatonin regulation in humans: evidence for a
novel circadian photoreceptor. The Journal of neuroscience, 21(16), 6405-6412.
Bubl, E., Kern, E., Ebert, D., Bach, M., & van Elst, L. T. (2010). Seeing gray when feeling
blue? Depression can be measured in the eye of the diseased. Biological Psychiatry,
68(2), 205-208.
Bubl, E., Kern, E., Ebert, D., Riedel, A., van Elst, L. T., & Bach, M. (2015). Retinal
dysfunction of contrast processing in major depression also apparent in cortical
activity. European Archives of Psychiatry and Clinical Neuroscience, 265(4), 343-
350.
Bubl, E., Tebartz Van Elst, L., Gondan, M., Ebert, D., & Greenlee, M. W. (2009). Vision in
depressive disorder. The World Journal of Biological Psychiatry, 10(4-2), 377-384.
Burgess, H. J., Fogg, L. F., Young, M. A., & Eastman, C. I. (2004). Bright light therapy for
winter depression - Is phase advancing beneficial? Chronobiology International,
21(4-5), 759-775.
85
Büttner, T., Kuhn, W., Patzold, T., & Przuntek, H. (1994). L-dopa improves colour vision in
Parkinson's disease. Journal of Neural Transmission - Parkinson's Disease and
Dementia Section, 7(1), 13-19.
Bye, C., Clubley, M., Henson, T., Peck, A., Smith, S., & Smith, S. (1979). Changes in the
human light reflex as a measure of the anticholinergic effects of drugs. A comparison
with other measures. European Journal of Clinical Pharmacology, 15(1), 21-25.
Campbell, S., Marriott, M., Nahmias, C., & MacQueen, G. M. (2004). Lower hippocampal
volume in patients suffering from depression: a meta-analysis. 161(4), 598-607.
Cao, D., & Barrionuevo, P. A. (2015a). 50.1: Invited Paper: The importance of melanopsin
activation in perception, health, and lighting design. SID Symposium Digest of
Technical Papers, 46.
Cao, D., & Barrionuevo, P. A. (2015b). Estimating photoreceptor excitations from spectral
outputs of a personal light exposure measurement device. Chronobiology
International, 32(2), 270-280.
Casten, R., & Rovner, B. (2008). Depression in age-related macular degeneration. Journal of
Visual Impairment & Blindness, 102(10), 591-599.
Chen, S. K., Badea, T. C., & Hattar, S. (2011). Photoentrainment and pupillary light reflex
are mediated by distinct populations of ipRGCs. Nature, 476(7358), 92-95.
Choe, C. J., Emslie, G. J., & Mayes, T. L. (2012). Depression. Child and Adolescent
Psychiatric Clinics of North America, 21(4), 807-807.
Chrousos, G. P. (1995). The hypothalamic–pituitary–adrenal axis and immune-mediated
inflammation. The New England journal of medicine, 332(20), 1351-1363.
Chrousos, G. P. (2009). Stress and disorders of the stress system. Nature Reviews
Endocrinology, 5(7), 374-381.
Cole, R. J., Kripke, D. F., Wisbey, J., Mason, W. J., Gruen, W., Hauri, P. J., & Juarez, S.
(1995). Seasonal Variation in Human Illumination Exposure at Two Different
Latitudes. Journal of Biological Rhythms, 10(4), 324-334.
Corral, M., Wardrop, A. A., Zhang, H., Grewal, A. K., & Patton, S. (2007). Morning light
therapy for postpartum depression. Archives of Women's Mental Health, 10(5), 221-
224.
Craig, L. A., & McDonald, R. J. (2008). Chronic disruption of circadian rhythms impairs
hippocampal memory in the rat. Brain Research Bulletin, 76(1–2), 141-151.
Crasson, M., Kjiri, S., Colin, A., Kjiri, K., L’Hermite-Baleriaux, M., Ansseau, M., & Legros,
J.-J. (2004). Serum melatonin and urinary 6-sulfatoxymelatonin in major depression.
Psychoneuroendocrinology, 29(1), 1-12.
Czeisler, C. A., Johnson, M. P., Duffy, J. F., Brown, E. N., Ronda, J. M., & Kronauer, R. E.
(1990). Exposure to bright light and darkness to treat physiologic maladaptation to
night work. New England Journal of Medicine, 322(18), 1253-1259.
Czeisler, C. A., Kronauer, R. E., Mooney, J. J., Anderson, J. L., & Allan, J. (1987). Biologic
rhythm disorders, depression, and phototherapy: a new hypothesis. Psychiatric Clinics
of North America, 10(4), 687-709.
Czeisler, C. A., Shanahan, T. L., Klerman, E. B., Martens, H., Brotman, D. J., Emens, J. S.,
Klein, T., & Rizzo, J. F. (1995a). Suppression of melatonin secretion in some blind
patients by exposure to bright light. New England Journal of Medicine, 332(1), 6-11.
Czeisler, C. A., & Waterhouse, J. (1995b). The effect of light on the human circadian
pacemaker. Circadian clocks and their adjustment, 183, 254-290.
Dacey, D. M., Liao, H.-W., Peterson, B. B., Robinson, F. R., Smith, V. C., Pokorny, J., Yau,
K.-W., & Gamlin, P. D. (2005). Melanopsin-expressing ganglion cells in primate
retina signal colour and irradiance and project to the LGN. Nature, 433(7027), 749-
754.
86
Davis, M., & Whalen, P. J. (2001). The amygdala: vigilance and emotion. Molecular
Psychiatry, 6(1), 13-34.
Deltito, J. A., Moline, M., Pollak, C., Martin, L. Y., & Maremmani, I. (1991). Effects of
phototherapy on non-seasonal unipolar and bipolar depressive spectrum disorders.
Journal of Affective Disorders, 23(4), 231-237.
Deppe, A. (2002). Treatment of depression with ocular light therapy. Psychotherapy in
Australia, 8(2), 66-67.
Devan, B. D., Goad, E. H., Petri, H. L., Antoniadis, E. A., Hong, N. S., Ko, C. H., Leblanc,
L., Lebovic, S. S., Lo, Q., & Ralph, M. R. (2001). Circadian phase-shifted rats show
normal acquisition but impaired long-term retention of place information in the water
task. Neurobiology of Learning and Memory, 75(1), 51-62.
Dkhissi-Benyahya, O., Coutanson, C., Knoblauch, K., Lahouaoui, H., Leviel, V., Rey, C.,
Bennis, M., & Cooper, H. M. (2013). The absence of melanopsin alters retinal clock
function and dopamine regulation by light. Cellular and Molecular Life Sciences,
70(18), 3435-3447.
Do, M. T. H., Kang, S. H., Xue, T., Zhong, H., Liao, H.-W., Bergles, D. E., & Yau, K.-W.
(2009). Photon capture and signalling by melanopsin retinal ganglion cells. Nature,
457(7227), 281-287.
Eastwood, M., & Peter, A. (1988). Epidemiology and seasonal affective disorder.
Psychological Medicine, 18(04), 799-806.
Ecker, J. L., Dumitrescu, O. N., Wong, K. Y., Alam, N. M., Chen, S.-K., LeGates, T., Renna,
J. M., Prusky, G. T., Berson, D. M., & Hattar, S. (2010). Melanopsin-expressing
retinal ganglion-cell photoreceptors: Cellular diversity and role in pattern vision.
Neuron, 67(1), 49-60.
Epperson, C. N., Terman, M., Terman, J. S., Hanusa, B. H., Oren, D. A., Peindl, K. S., &
Wisner, K. L. (2004). Randomized clinical trial of bright light therapy for antepartum
depression: Preliminary findings. Journal of Clinical Psychiatry, 65(3), 421-425.
Espiritu, R. C., Kripke, D. F., Ancoli-Israel, S., Mowen, M. A., Mason, W. J., Fell, R. L.,
Klauber, M. R., & Kaplan, O. J. (1994). Low illumination experienced by San Diego
adults: Association with atypical depressive symptoms. Biological Psychiatry, 35(6),
403-407.
Esposito, E. (2006). Serotonin-dopamine interaction as a focus of novel antidepressant drugs.
Current Drug Targets, 7(2), 177-185.
Estevez, M. E., Fogerson, P. M., Ilardi, M. C., Borghuis, B. G., Chan, E., Weng, S.,
Auferkorte, O. N., Demb, J. B., & Berson, D. M. (2012). Form and function of the M4
cell, an intrinsically photosensitive retinal ganglion cell type contributing to
geniculocortical vision. The Journal of neuroscience, 32(39), 13608-13620.
Even, C., Schröder, C. M., Friedman, S., & Rouillon, F. (2008). Efficacy of light therapy in
nonseasonal depression: A systematic review. Journal of Affective Disorders, 108(1),
11-23.
Fam, J., Rush, A. J., Haaland, B., Barbier, S., & Luu, C. (2013). Visual contrast sensitivity in
major depressive disorder. Journal of Psychosomatic Research, 75(1), 83-86.
Feigl, B., Mattes, D., Thomas, R., & Zele, A. J. (2011). Intrinsically photosensitive
(melanopsin) retinal ganglion cell function in glaucoma. Investigative Ophthalmology
and Visual Science, 52(7), 4362-4367.
Feigl, B., & Zele, A. J. (2014). Melanopsin-expressing intrinsically photosensitive retinal
ganglion cells in retinal disease. Optometry and Vision Science, 91(8), 894-903.
Feigl, B., Zele, A. J., Fader, S. M., Howes, A. N., Hughes, C. E., Jones, K. A., & Jones, R.
(2012). The post‐illumination pupil response of melanopsin‐expressing intrinsically
87
photosensitive retinal ganglion cells in diabetes. Acta Ophthalmologica, 90(3), e230-
e234.
Fekete, M., Van Ree, J. M., Niesink, R. J., & de Wied, D. (1985). Disrupting circadian
rhythms in rats induces retrograde amnesia. Physiology & Behavior, 34(6), 883-887.
Fernandez, D. C., Chang, Y.-T., Hattar, S., & Chen, S.-K. (2016). Architecture of retinal
projections to the central circadian pacemaker. Proceedings of the National Academy
of Sciences, 113(21), 6047-6052.
Ferrari, A. J., Somerville, A. J., Baxter, A. J., Norman, R., Patten, S. B., Vos, T., &
Whiteford, H. A. (2013). Global variation in the prevalence and incidence of major
depressive disorder: A systematic review of the epidemiological literature.
Psychological Medicine, 43(3), 471-481.
Fonken, L. K., Finy, M. S., Walton, J. C., Weil, Z. M., Workman, J. L., Ross, J., & Nelson,
R. J. (2009). Influence of light at night on murine anxiety-and depressive-like
responses. Behavioural Brain Research, 205(2), 349-354.
Fonken, L. K., Kitsmiller, E., Smale, L., & Nelson, R. J. (2012). Dim night time light impairs
cognition and provokes depressive-like responses in a diurnal rodent. Journal of
Biological Rhythms, 27(4), 319-327.
Friedman, S., Even, C., Dardennes, R., & Guelfi, J. D. (2004). Light therapy, nonseasonal
depression, and night eating syndrome [10]. Canadian Journal of Psychiatry, 49(11),
790-790.
Fujioka, A., Fujioka, T., Tsuruta, R., Izumi, T., Kasaoka, S., & Maekawa, T. (2011). Effects
of a constant light environment on hippocampal neurogenesis and memory in mice.
Neuroscience Letters, 488(1), 41-44.
Galindo-Romero, C., Jiménez-López, M., Garcia-Ayuso, D., Salinas-Navarro, M., Nadal-
Nicolás, F., Agudo-Barriuso, M., Villegas-Pérez, M., Avilés-Trigueros, M., & Vidal-
Sanz, M. (2013). Number and spatial distribution of intrinsically photosensitive
retinal ganglion cells in the adult albino rat. Experimental Eye Research, 108, 84-93.
Gallin, P. F., Terman, M., Reme, C. E., Rafferty, B., Terman, J. S., & Burde, R. M. (1995).
Ophthalmologic examination of patients with seasonal affective disorder, before and
after bright light therapy. American Journal of Ophthalmology, 119(2), 202-210.
Gamlin, P. D. R., McDougal, D. H., Pokorny, J., Smith, V. C., Yau, K. W., & Dacey, D. M.
(2007). Human and macaque pupil responses driven by melanopsin-containing retinal
ganglion cells. Vision Research, 47(7), 946-954.
Gamlin, P. D. R., Zhang, H., & Clarke, R. J. (1995). Luminance neurons in the pretectal
olivary nucleus mediate the pupillary light reflex in the rhesus monkey. Experimental
Brain Research, 106(1), 177-180.
Gillin, J. C. (1979). REM architecture changes in bipolar and unipolar depression. REM, 2(3),
4.
Girgus, J. S., & Yang, K. (2015). Gender and depression. Current Opinion in Psychology, 4,
53-60.
Glickman, G., Byrne, B., Pineda, C., Hauck, W. W., & Brainard, G. C. (2006). Light therapy
for seasonal affective disorder with blue narrow-band light-emitting diodes (LEDs).
Biological Psychiatry, 59(6), 502-507.
Goel, N., Terman, M., Terman, J. S., Macchi, M. M., & Stewart, J. W. (2005). Controlled
trial of bright light and negative air ions for chronic depression. Psychological
Medicine, 35(07), 945-955.
Goldberg, D. (2006). The aetiology of depression. Psychological Medicine, 36(10), 1341-
1347.
Golden, R. N., Gaynes, B. N., Ekstrom, R. D., Hamer, R. M., Jacobsen, F. M., Suppes, T.,
Wisner, K. L., & Nemeroff, C. B. (2005). The efficacy of light therapy in the
88
treatment of mood disorders: a review and meta-analysis of the evidence. American
Journal of Psychiatry, 162(4), 656-662.
Goldman, B. D. (2001). Mammalian photoperiodic system: formal properties and
neuroendocrine mechanisms of photoperiodic time measurement. Journal of
Biological Rhythms, 16(4), 283-301.
Gooley, J. J., Lu, J., Chou, T. C., Scammell, T. E., & Saper, C. B. (2001). Melanopsin in cells
of origin of the retinohypothalamic tract. Nature Neuroscience, 4(12), 1165-1165.
Gooley, J. J., Lu, J., Fischer, D., & Saper, C. B. (2003). A broad role for melanopsin in
nonvisual photoreception. The Journal of neuroscience, 23(18), 7093-7106.
Gou, Z., Lau, S. S. Y., & Qian, F. (2015). Comparison of mood and task performance in
naturally-lit and artificially-lit environments. Indoor and Built Environment, 24(1),
27-36.
Graw, P., Recker, S., Sand, L., Kräuchi, K., & Wirz-Justice, A. (1999). Winter and summer
outdoor light exposure in women with and without seasonal affective disorder.
Journal of Affective Disorders, 56(2–3), 163-169.
Guillemette, J., Hébert, M., Paquet, J., & Dumont, M. (1998). Natural bright light exposure in
the summer and winter in subjects with and without complaints of seasonal mood
variations. Biological Psychiatry, 44(7), 622-628.
Guinjoan, S. M., Bernabó, J. L., & Cardinali, D. P. (1995). Cardiovascular tests of autonomic
function and sympathetic skin responses in patients with major depression. Journal of
Neurology, Neurosurgery and Psychiatry, 59(3), 299-302.
Haffmans, J., Schouten, M., & den Hoed, L. (2008). Treating depression with light therapy
during pregnancy. Journal of Affective Disorders, 107, S86-S87.
Hamel, C. P. (2007). Cone rod dystrophies. Orphanet Journal of Rare Diseases, 2(1), 7.
Hannibal, J., Hindersson, P., Østergaard, J., Georg, B., Heegaard, S., Larsen, P. J., &
Fahrenkrug, J. (2004). Melanopsin is expressed in PACAP-containing retinal ganglion
cells of the human retinohypothalamic tract. Investigative Ophthalmology and Visual
Science, 45(11), 4202-4209.
Hansen, M. S., Sander, B., Kessel, L., Broendsted, A. E., Kawasaki, A., Herbst, K.,
LundAndersen, H., Medicinska, f., & Oftalmiatrik. (2012). Intrinsically
photosensitive retinal ganglion cell function in relation to age: A pupillometric study
in humans with special reference to the age-related optic properties of the lens. BMC
Ophthalmology, 12(4).
Harb, F., Hidalgo, M. P., & Martau, B. (2015). Lack of exposure to natural light in the
workspace is associated with physiological, sleep and depressive symptoms.
Chronobiology International, 32(3), 368-375.
Harnois, C., & Di Paolo, T. (1990). Decreased dopamine in the retinas of patients with
Parkinson's disease. Investigative Ophthalmology and Visual Science, 31(11), 2473-
2475.
Harrington, M. E. (1997). The ventral lateral geniculate nucleus and the intergeniculate
leaflet: Interrelated structures in the visual and circadian systems. Neuroscience &
Biobehavioral Reviews, 21(5), 705-727.
Hattar, S., Kumar, M., Park, A., Tong, P., Tung, J., Yau, K.-W., & Berson, D. M. (2006).
Central projections of melanopsin-expressing retinal ganglion cells in the mouse. The
Journal of Comparative Neurology, 497(3), 326-349.
Hattar, S., Liao, H. W., Takao, M., Berson, D. M., & Yau, K. W. (2002). Melanopsin-
containing retinal ganglion cells: Architecture, projections, and intrinsic
photosensitivity. Science, 295(5557), 1065-1070.
89
Hébert, M., Beattie, C. W., Tam, E. M., Yatham, L. N., & Lam, R. W. (2004).
Electroretinography in patients with winter seasonal affective disorder. Psychiatry
Research, 127(1–2), 27-34.
Hebert, M., Dumont, M., & Lachapelle, P. (2002). Electrophysiological evidence suggesting
a seasonal modulation of retinal sensitivity in subsyndromal winter depression.
Journal of Affective Disorders, 68(2-3), 191-202.
Hébert, M., Dumont, M., & Lachapelle, P. (2002). Electrophysiological evidence suggesting
a seasonal modulation of retinal sensitivity in subsyndromal winter depression.
Journal of Affective Disorders, 68(2–3), 191-202.
Herbst, K., Sander, B., Lund-Andersen, H., Broendsted, A. E., Kessel, L., Hansen, M. S., &
Kawasaki, A. (2012). Intrinsically photosensitive retinal ganglion cell function in
relation to age: a pupillometric study in humans with special reference to the age-
related optic properties of the lens. BMC Ophthalmology, 12(1).
Ikeda, H., Head, G., & Ellis, C. K. (1994). Electrophysiological signs of retinal dopamine
deficiency in recently diagnosed Parkinson's disease and a follow up study. Vision
Research, 34(19), 2629-2638.
Jackson, C. R., Ruan, G.-X., Aseem, F., Abey, J., Gamble, K., Stanwood, G., Palmiter, R. D.,
Iuvone, P. M., & McMahon, D. G. (2012). Retinal dopamine mediates multiple
dimensions of light-adapted vision. The Journal of neuroscience, 32(27), 9359-9368.
Jardim, A. C. N., Pawley, M. D. M., Cheeseman, J. F., Guesgen, M. J., Steele, C. T., &
Warman, G. R. (2011). Validating the use of wrist-level light monitoring for in-
hospital circadian studies. Chronobiology International, 28(9), 834-840.
Joo, H. R., Peterson, B. B., Dacey, D. M., Hattar, S., & Chen, S.-K. (2013). Recurrent axon
collaterals of intrinsically photosensitive retinal ganglion cells. Visual Neuroscience,
30(4), 175-182.
Joyce, D. S., Feigl, B., Cao, D., & Zele, A. J. (2015). Temporal characteristics of melanopsin
inputs to the human pupil light reflex. Vision Research, 107, 58-66.
Joyce, D. S., Feigl, B., & Zele, A. J. (2012). Temporal summation of Intrinsically
Photosensitive Retinal Ganglion Cells (ipRGC) contribution to human Pupil Light
Reflex. CLINICAL AND EXPERIMENTAL OPHTHALMOLOGY, 40, 137-137.
Joyce, D. S., Feigl, B., & Zele, A. J. (2016a). The effects of short-term light adaptation on the
human post-illumination pupil response. Investigative Ophthalmology and Visual
Science, 57(13), 5672-5680.
Joyce, D. S., Feigl, B., & Zele, A. J. (2016b). Melanopsin-mediated post-illumination pupil
response in the peripheral retina. Journal of Vision, 16(8), 5-5.
Jusuf, P. R., Lee, S. C. S., Hannibal, J., & Grünert, U. (2007). Characterization and synaptic
connectivity of melanopsin-containing ganglion cells in the primate retina. European
Journal of Neuroscience, 26(10), 2906-2921.
Kankipati, L. (2009). Sustained pupil constriction following brief light exposure: Relation to
retinal health. (Dissertation/Thesis), ProQuest, UMI Dissertations Publishing.
Retrieved from http://qut.summon.serialssolutions.com
Kankipati, L., Girkin, C. A., & Gamlin, P. D. (2010). Post-illumination pupil response in
subjects without ocular disease. Investigative Ophthalmology and Visual Science,
51(5), 2764-2769.
Kankipati, L., Girkin, C. A., & Gamlin, P. D. (2011). The post-illumination pupil response is
reduced in glaucoma patients. Investigative Ophthalmology and Visual Science, 52(5),
2287-2292.
Karatsoreos, I. N., & McEwen, B. S. (2011). Psychobiological allostasis: resistance,
resilience and vulnerability. Trends in Cognitive Sciences, 15(12), 576-584.
90
Kardon, R., Anderson, S. C., Damarjian, T. G., Grace, E. M., Stone, E., & Kawasaki, A.
(2009). Chromatic pupil responses: Preferential activation of the melanopsin-
mediated versus outer photoreceptor-mediated pupil light reflex. Ophthalmology,
116(8), 1564-1573.
Kardon, R., Anderson, S. C., Damarjian, T. G., Grace, E. M., Stone, E., & Kawasaki, A.
(2011). Chromatic pupillometry in patients with retinitis pigmentosa. Ophthalmology,
118(2), 376-381.
Kasper, S., Wehr, T. A., Bartko, J. J., Gaist, P. A., & Rosenthal, N. E. (1989).
Epidemiological findings of seasonal changes in mood and behavior: A telephone
survey of Montgomery County, Maryland. Archives of General Psychiatry, 46(9),
823.
Keeler, C. E. (1927). Iris movements in blind mice. American Journal of Physiology--Legacy
Content, 81(1), 107-112.
Kelbsch, C., Maeda, F., Strasser, T., Blumenstock, G., Wilhelm, B., Wilhelm, H., & Peters,
T. (2016). Pupillary responses driven by ipRGCs and classical photoreceptors are
impaired in glaucoma. Graefe's Archive for Clinical and Experimental
Ophthalmology, 254(7), 1361-1370.
Khurana, R. N., Porco, T. C., Claman, D. M., Boldrey, E. E., Palmer, J. D., & Wieland, M. R.
(2016). Increasing sleep duration is associated with geographic atrophy and age-
related macular degeneration. Retina, 36(2), 255-258.
Kräuchi, K., Wirz-Justice, A., & Graw, P. (1990). The relationship of affective state to
dietary preference: winter depression and light therapy as a model. Journal of
Affective Disorders, 20(1), 43-53.
Kripke, D. F., Mullaney, D. J., Klauber, M. R., Craig Risch, S., & Christian Gillin, J. (1992).
Controlled trial of bright light for nonseasonal major depressive disorders. Biological
Psychiatry, 31(2), 119-134.
Kuze, M., Morita, T., Fukuda, Y., Kondo, M., Tsubota, K., & Ayaki, M. (2016).
Electrophysiological responses from intrinsically photosensitive retinal ganglion cells
are diminished in glaucoma patients. Journal of Optometry.
Lam, R. W., Beattie, C. W., Buchanan, A., & Mador, J. A. (1992). Electroretinography in
seasonal affective disorder. Psychiatry Research, 43(1), 55-63.
Lam, R. W., & Levitan, R. D. (2000). Pathophysiology of seasonal affective disorder: a
review. Journal of Psychiatry and Neuroscience, 25(5), 469.
Lam, R. W., Levitt, A. J., Levitan, R. D., Enns, M. W., Morehouse, R., Michalak, E. E., &
Tam, E. M. (2006). The Can-SAD study: a randomized controlled trial of the
effectiveness of light therapy and fluoxetine in patients with winter seasonal affective
disorder. American Journal of Psychiatry, 163(5), 805-812.
Lambert, G. W., Reid, C., Kaye, D. M., Jennings, G. L., & Esler, M. D. (2002). Effect of
sunlight and season on serotonin turnover in the brain. The Lancet, 360(9348), 1840-
1842.
Laurenzo, S. A., Kardon, R., Ledolter, J., Poolman, P., Schumacher, A. M., Potash, J. B.,
Full, J. M., Rice, O., Ketcham, A., Starkey, C., & Fiedorowicz, J. G. (2016). Pupillary
response abnormalities in depressive disorders. Psychiatry Research, 246, 492-499.
Lavoie, J., Illiano, P., Sotnikova, T. D., Gainetdinov, R. R., Beaulieu, J.-M., & Hébert, M.
(2014). The Electroretinogram as a Biomarker of Central Dopamine and Serotonin:
Potential Relevance to Psychiatric Disorders. Biological Psychiatry, 75(6), 479-486.
Lavoie, M.-P., Lam, R. W., Bouchard, G., Sasseville, A., Charron, M.-C., Gagné, A.-M.,
Tremblay, P., Filteau, M.-J., & Hébert, M. (2009). Evidence of a biological effect of
light therapy on the retina of patients with seasonal affective disorder. Biological
Psychiatry, 66(3), 253-258.
91
Lecrubier, Y., Sheehan, D., Hergueta, T., & Weiller, E. (1998). The mini international
neuropsychiatric interview. European Psychiatry, 13, 198s-198s.
Lecrubier, Y., Sheehan, D. V., Weiller, E., Amorim, P., Bonora, I., Harnett Sheehan, K.,
Janavs, J., & Dunbar, G. C. (1997). The Mini International Neuropsychiatric
Interview (MINI). A short diagnostic structured interview: reliability and validity
according to the CIDI. European Psychiatry, 12(5), 224-231.
Legates, T. A., Altimus, C. M., Wang, H., Lee, H.-K., Yang, S., Zhao, H., Kirkwood, A.,
Weber, E. T., & Hattar, S. (2012). Aberrant light directly impairs mood and learning
through melanopsin-expressing neurons. Nature, 491(7425), 594-598.
LeGates, T. A., Fernandez, D. C., & Hattar, S. (2014). Light as a central modulator of
circadian rhythms, sleep and affect. Nature Reviews Neuroscience, 15(7), 443-454.
Lemoine, P., Guilleminault, C., & Alvarez, E. (2007). Improvement in subjective sleep in
major depressive disorder with a novel antidepressant, agomelatine: randomized,
double-blind comparison with venlafaxine. Journal of Clinical Psychiatry, 68(11),
1723-1732.
Lewy, A. J., Bauer, V. K., Cutler, N. L., & et al. (1998). Morning vs evening light treatment
of patients with winter depression. Archives of General Psychiatry, 55(10), 890-896.
Lewy, A. J., Sack, R. L., Miller, L. S., & Hoban, T. M. (1987). Antidepressant and circadian
phase-shifting effects of light. Science, 235(4786), 352-354.
Liao, H. W., Ren, X., Peterson, B. B., Marshak, D. W., Yau, K. W., Gamlin, P. D., & Dacey,
D. M. (2016). Melanopsin‐expressing ganglion cells on macaque and human retinas
form two morphologically distinct populations. Journal of Comparative Neurology,
524(14), 2845–2872
Liebman, P. A., Parker, K. R., & Dratz, E. A. (1987). The molecular mechanism of visual
excitation and its relation to the structure and composition of the rod outer segment.
Annual Review of Physiology, 49(1), 765-791.
Lieverse, R., Van Someren, E. J., Nielen, M. M., Uitdehaag, B. M., Smit, J. H., &
Hoogendijk, W. J. (2011). Bright light treatment in elderly patients with nonseasonal
major depressive disorder: a randomized placebo-controlled trial. Archives of General
Psychiatry, 68(1), 61-70.
Linkowski, P., Mendlewicz, J., Leclercq, R., Brasseur, M., Hubain, P., Golstein, J.,
Copinschi, G., & Cauter, E. V. (1985). The 24-hour profile of adrenocorticotropin and
cortisol in major depressive iIllness. The Journal of Clinical Endocrinology and
Metabolism, 61(3), 429-438.
Lockley, S. W., Skene, D. J., Arendt, J., Tabandeh, H., Bird, A. C., & Defrance, R. (1997).
Relationship between melatonin rhythms and visual loss in the blind 1. The Journal of
Clinical Endocrinology and Metabolism, 82(11), 3763-3770.
Loewenfeld, I. E., & Lowenstein, O. (1993). The pupil: Anatomy, physiology, and clinical
applications (Vol. 2): Wiley-Blackwell.
Lovato, N., & Gradisar, M. (2014). A meta-analysis and model of the relationship between
sleep and depression in adolescents: Recommendations for future research and
clinical practice. Sleep Medicine Reviews, 18(6), 521-529.
Loving, R. T., Kripke, D. F., Elliott, J. A., Knickerbocker, N. C., & Grandner, M. A. (2005).
Bright light treatment of depression for older adults BMC Psychiatry, 5(1).
Lucas, R. J., Peirson, S. N., Berson, D. M., Brown, T. M., Cooper, H. M., Czeisler, C. A.,
Figueiro, M. G., Gamlin, P. D., Lockley, S. W., O’Hagan, J. B., Price, L. L. A.,
Provencio, I., Skene, D. J., & Brainard, G. C. (2014). Measuring and using light in the
melanopsin age. Trends in Neurosciences, 37(1), 1-9.
Luppa, M., Sikorski, C., Luck, T., Ehreke, L., Konnopka, A., Wiese, B., Weyerer, S., König,
H.-H., & Riedel-Heller, S. G. (2012). Age-and gender-specific prevalence of
92
depression in latest-life–systematic review and meta-analysis. Journal of Affective
Disorders, 136(3), 212-221.
Madsen, H. O., Dam, H., & Hageman, I. (2015). High prevalence of seasonal affective
disorder among persons with severe visual impairment. British Journal of Psychiatry.
Magnusson, A. (2000). An overview of epidemiological studies on seasonal affective
disorder. Acta Psychiatrica Scandinavica, 101(3), 176-184.
Magnusson, A., Friis, S., & Opjordsmoen, S. (1997). Internal consistency of the seasonal
pattern assessment questionnaire (SPAQ). Journal of Affective Disorders, 42(2), 113-
116.
Markwell, E. L., Feigl, B., & Zele, A. J. (2010). Intrinsically photosensitive melanopsin
retinal ganglion cell contributions to the pupillary light reflex and circadian rhythm.
Clinical and Experimental Optometry, 93(3), 137-149.
Marmor, M., & Hock, P. (1982). A practical method for c-wave recording in man.
Techniques in Clinical Electrophysiology of Vision, 31, 67.
Martin, S. K., & Eastman, C. I. (2002). Sleep logs of young adults with self-selected sleep
times predict the dim light melatonin onset. Chronobiology International, 19(4), 695-
707.
Martiny, K., Lunde, M., Unden, M., Dam, H., & Bech, P. (2005). Adjunctive bright light in
non‐seasonal major depression: results from clinician‐rated depression scales. Acta
Psychiatrica Scandinavica, 112(2), 117-125.
Matsumoto, M., & Hikosaka, O. (2007). Lateral habenula as a source of negative reward
signals in dopamine neurons. Nature, 447(7148), 1111-1115.
Maynard, M. L., Zele, A. J., & Feigl, B. (2015). Melanopsin-mediated post-illumination pupil
response in early age-related macular degeneration in early AMD. Investigative
Ophthalmology and Visual Science, 56(11), 6906-6913.
McDougal, D. H., & Gamlin, P. D. (2010). The influence of intrinsically-photosensitive
retinal ganglion cells on the spectral sensitivity and response dynamics of the human
pupillary light reflex. Vision Research, 50(1), 72-87.
McDougal, D. H., & Gamlin, P. D. (2015). Autonomic control of the eye. Compr Physiol,
5(1), 439-473.
Meesters, Y., Dekker, V., Schlangen, L. J., Bos, E. H., & Ruiter, M. J. (2011). Low-intensity
blue-enriched white light (750 lux) and standard bright light (10 000 lux) are equally
effective in treating SAD. A randomized controlled study. BMC Psychiatry, 11(1), 17.
Miller, A. M., Obermeyer, W. H., Behan, M., & Benca, R. M. (1998). The superior
colliculus–pretectum mediates the direct effects of light on sleep. Proceedings of the
National Academy of Sciences, 95(15), 8957-8962.
Miller, R., & Dowling, J. (1970). Intracellular responses of the Müller (glial) cells of
mudpuppy retina: their relation to b-wave of the electroretinogram. Journal of
Neurophysiology, 33(3), 323-341.
Moore, R. Y. (1996). Neural control of the pineal gland. Behavioural Brain Research, 73(1-
2), 125-130.
Münch, M., Kourti, P., Brouzas, D., & Kawasaki, A. (2016). Variation in the pupil light
reflex between winter and summer seasons. Acta Ophthalmologica, 94(3), e244-246.
Münch, M., Léon, L., Crippa, S. V., & Kawasaki, A. (2012). Circadian and Wake-Dependent
Effects on the Pupil Light Reflex in Response to Narrow-Bandwidth Light
PulsesPupil Light Reflex Response. Investigative Ophthalmology and Visual Science,
53(8), 4546-4555.
Mure, L. S., Rieux, C., Hattar, S., & Cooper, H. M. (2007). Melanopsin-dependent nonvisual
responses: evidence for photopigment bistability in vivo. Journal of Biological
Rhythms, 22(5), 411-424.
93
Nader, N., Chrousos, G. P., & Kino, T. (2010). Interactions of the circadian clock system and
the HPA axis. Trends in Endocrinology and Metabolism, 21(5), 277-286.
Naus, T., Burger, A., Malkoc, A., Molendijk, M., & Haffmans, J. (2013). Is there a difference
in clinical efficacy of bright light therapy for different types of depression? A pilot
study. Journal of Affective Disorders, 151(3), 1135-1137.
Nelson, R. J., & Zucker, I. (1981). Absence of extraocular photoreception in diurnal and
nocturnal rodents exposed to direct sunlight. Comparative Biochemistry and
Physiology Part A: Physiology, 69(1), 145-148.
Nygaard, R. W., & Frumkes, T. E. (1982). Calibration of the retinal illuminance provided by
maxwellian views. Vision Research, 22(4), 433-434.
Obara, E. A., Hannibal, J., Heegaard, S., & Fahrenkrug, J. (2016). Loss of melanopsin-
expressing retinal ganglion cells in severely staged glaucoma patients. Investigative
Ophthalmology and Visual Science, 57(11), 4661-4667.
Oren, D. A., Joseph-Vanderpool, J. R., & Rosenthal, N. E. (1991). Adaptation to dim light in
depressed patients with seasonal affective disorder. Psychiatry Research, 36(2), 187-
193.
Oren, D. A., Moul, D. E., Schwartz, P. J., Alexander, J. R., Yatnada, E. M., & Rosenthal, N.
E. (1993). An investigation of ophthalmic function in winter seasonal affective
disorder. Depression, 1(1), 29-37.
Oren, D. A., Moul, D. E., Schwartz, P. J., Brown, C., Yamada, E. M., & Rosenthal, N. E.
(1994). Exposure to ambient light in patients with winter seasonal affective disorder.
American Journal of Psychiatry, 151(4), 591-593.
Ozaki, N., Rosenthal, N. E., Moul, D. E., Schwartz, P. J., & Oren, D. A. (1993). Effects of
phototherapy on electrooculographic ratio in winter seasonal affective disorder.
Psychiatry Research, 49(2), 99-107.
Park, J. C., & McAnany, J. J. (2015). Effect of stimulus size and luminance on the rod-, cone-
, and melanopsin-mediated pupillary light reflex. Journal of Vision, 15(3).
Park, J. C., Moura, A. L., Raza, A. S., Rhee, D. W., Kardon, R. H., & Hood, D. C. (2011).
Toward a clinical protocol for assessing rod, cone, and melanopsin contributions to
the human pupil response. Investigative Ophthalmology and Visual Science, 52(9),
6624-6635.
Pelli, D., & Robson, J. (1988). The design of a new letter chart for measuring contrast
sensitivity. Clinical Vision Sciences, 2(3), 187-199.
Pérez-Canales, J. L., Rico-Sergado, L., & Pérez-Santonja, J. J. (2016). Self-reported sleep
duration in patients with neovascular age-related macular degeneration. Ophthalmic
Epidemiology, 23(1), 20-26.
Phillips, M. A., Bitsios, P., Szabadi, E., & Bradshaw, C. M. (2000). Comparison of the
antidepressants reboxetine, fluvoxamine and amitriptyline upon spontaneous pupillary
fluctuations in healthy human volunteers. Psychopharmacology, 149(1), 72-76.
Pinninti, N. R., Madison, H., Musser, E., & Rissmiller, D. (2003). MINI International
Neuropsychiatric Schedule: Clinical utility and patient acceptance. European
Psychiatry, 18(7), 361-364.
Price, M. J., Feldman, R. G., Adelberg, D., & Kayne, H. (1992). Abnormalities in color
vision and contrast sensitivity in Parkinson's disease. Neurology, 42(4), 887.
Prigge, C. L., Yeh, P.-T., Liou, N.-F., Lee, C.-C., You, S.-F., Liu, L.-L., McNeill, D. S.,
Chew, K. S., Hattar, S., Chen, S.-K., & Zhang, D.-Q. (2016). M1 ipRGCs Influence
Visual Function through Retrograde Signaling in the Retina. The Journal of
neuroscience, 36(27), 7184-7197.
94
Provencio, I., Jiang, G., De Grip, W. J., Hayes, W. P., & Rollag, M. D. (1998). Melanopsin:
An opsin in melanophores, brain, and eye. Proceedings of the National Academy of
Sciences, 95(1), 340-345.
Provencio, I., Rollag, M. D., & Castrucci, A. M. (2002). Anatomy: Photoreceptive net in the
mammalian retina. Nature, 415(6871), 493-493.
Richelson, E. (1994). Pharmacology of antidepressants—Characteristics of the ideal drug.
Mayo Clinic Proceedings, 69(11), 1069-1081.
Roecklein, K., Wong, P., Ernecoff, N., Miller, M., Donofry, S., Kamarck, M., Wood-Vasey,
W. M., & Franzen, P. (2013). The post illumination pupil response is reduced in
seasonal affective disorder. Psychiatry Research, 210(1), 150-158.
Rohan, K. J., Rough, J. N., Evans, M., Ho, S.-Y., Meyerhoff, J., Roberts, L. M., & Vacek, P.
M. (2016). A protocol for the Hamilton Rating Scale for Depression: Item scoring
rules, rater training, and outcome accuracy with data on its application in a clinical
trial. Journal of Affective Disorders, 200, 111-118.
Rollag, M. D. (1996). Amphibian melanophores become photosensitive when treated with
retinal. Journal of Experimental Zoology, 275(1), 20-26.
Royer, M., Ballentine, N. H., Eslinger, P. J., Houser, K., Mistrick, R., Behr, R., & Rakos, K.
(2012). Light therapy for seniors in long term care. Journal of the American Medical
Directors Association, 13(2), 100-102.
Russo, S. J., & Nestler, E. J. (2013). The brain reward circuitry in mood disorders. Nature
Reviews: Neuroscience, 14(9), 609-625.
Sadeh, A., & Acebo, C. (2002). The role of actigraphy in sleep medicine. Sleep Medicine
Reviews, 6(2), 113-124.
Sara, Susan J., & Bouret, S. (2012). Orienting and reorienting: The Locus Coeruleus mediates
cognition through arousal. Neuron, 76(1), 130-141.
Savides, T. J., Messin, S., Senger, C., & Kripke, D. F. (1986). Natural light exposure of
young adults. Physiology and Behavior, 38(4), 571-574.
Schmidt, T. M., Chen, S.-K., & Hattar, S. (2011a). Intrinsically photosensitive retinal
ganglion cells: Many subtypes, diverse functions. Trends in Neurosciences, 34(11),
572-580.
Schmidt, T. M., & Kofuji, P. (2009). Functional and morphological differences among
intrinsically photosensitive retinal ganglion cells. The Journal of neuroscience, 29(2),
476-482.
Schmidt, T. M., & Kofuji, P. (2010). Differential cone pathway influence on intrinsically
photosensitive retinal ganglion cell subtypes. The Journal of neuroscience, 30(48),
16262-16271.
Schmidt, T. M., & Kofuji, P. (2011b). Structure and function of bistratified intrinsically
photosensitive retinal ganglion cells in the mouse. Journal of Comparative Neurology,
519(8), 1492-1504.
Schmidt, T. M., Taniguchi, K., & Kofuji, P. (2008). Intrinsic and extrinsic light responses in
melanopsin-expressing ganglion cells during mouse development. Journal of
Neurophysiology, 100(1), 371-384.
Schmidtke, J. I. (Producer). (2013, 6/7/2015). Stress, depression, dnxiety & PTSD - Part 1.
Retrieved from https://www.youtube.com/watch?v=36ELSaN2fdA
Schmitt, J. A., Riedel, W. J., Vuurman, E. F., Kruizinga, M., & Ramaekers, J. G. (2002).
Modulation of the critical flicker fusion effects of serotonin reuptake inhibitors by
concomitant pupillary changes. Psychopharmacology, 160(4), 381-386.
Schultz, W., Dayan, P., & Montague, P. R. (1997). A Neural substrate of prediction and
reward. Science, 275(5306), 1593-1599.
95
Seldenrijk, R., Hup, D. R., de Graan, P. N., & van de Veerdonk, F. C. (1979). Morphological
and physiological aspects of melanophores in primary culture from tadpoles of
Xenopus laevis. Cell and Tissue Research, 198(3), 397-409.
Shirani, A., & St Louis, E. K. (2009). Illuminating rationale and uses for light therapy.
Journal of Clinical Sleep Medicine, 5(2), 155-163.
Shochat, T., Martin, J., Marler, M., & Ancoli-Israel, S. (2000). Illumination levels in nursing
home patients: effects on sleep and activity rhythms. Journal of Sleep Research, 9(4),
373-379.
Siepmann, T., Ziemssen, T., Mueck-Weymann, M., Kirch, W., & Siepmann, M. (2007). The
effects of venlafaxine on autonomic functions in healthy volunteers. Journal of
Clinical Psychopharmacology, 27(6), 687-691.
Smolders, K. C. H. J., De Kort, Y. A. W., & Van den Berg, S. M. (2013). Daytime light
exposure and feelings of vitality: Results of a field study during regular weekdays.
Journal of Environmental Psychology, 36, 270-279.
Srinivasan, V., Smits, M., Spence, W., Lowe, A. D., Kayumov, L., Pandi-Perumal, S. R.,
Parry, B., & Cardinali, D. P. (2006). Melatonin in mood disorders. The World Journal
of Biological Psychiatry, 7(3), 138-151.
Steinhauer, S. R., Siegle, G. J., Condray, R., & Pless, M. (2004). Sympathetic and
parasympathetic innervation of pupillary dilation during sustained processing.
International Journal of Psychophysiology, 52(1), 77-86.
Storch, E. A., Roberti, J. W., & Roth, D. A. (2004). Factor structure, concurrent validity, and
internal consistency of the beck depression inventory—second edition in a sample of
college students. Depression and Anxiety, 19(3), 187-189.
Szabó, Z., Antal, A., Tokaji, Z., Kálmán, J., Kéri, S., Benedek, G., & Janka, Z. (2004). Light
therapy increases visual contrast sensitivity in seasonal affective disorder. Psychiatry
Research, 126(1), 15-21.
Tataroğlu, Ö., Aksoy, A., Yılmaz, A., & Canbeyli, R. (2004). Effect of lesioning the
suprachiasmatic nuclei on behavioral despair in rats. Brain Research, 1001(1), 118-
124.
Teclemariam‐Mesbah, R., Ter Horst, G. J., Postema, F., Wortel, J., & Buijs, R. M. (1999).
Anatomical demonstration of the suprachiasmatic nucleus–pineal pathway. The
Journal of Comparative Neurology, 406(2), 171-182.
Terman, J. S., & Terman, M. (1999). Photopic and scotopic light detection in patients with
seasonal affective disorder and control subjects. Biological Psychiatry, 46(12), 1642-
1648.
Terman, J. S., Terman, M., Lo, E.-S., & Cooper, T. B. (2001). Circadian time of morning
light administration and therapeutic response in winter depression. Archives of
General Psychiatry, 58(1), 69-75.
Terman, M., & Terman, J. S. (2005). Light therapy for seasonal and nonseasonal depression:
Efficacy, protocol, safety, and side effects. CNS Spectrums, 10(8), 647-663.
Terman, M., Terman, J. S., & Rafferty, B. (1990). Experimental design and measures of
success in the treatment of winter depression by bright light. Psychopharmacology
Bulletin.
Thapan, K., Arendt, J., & Skene, D. J. (2001). An action spectrum for melatonin suppression:
evidence for a novel non‐rod, non‐cone photoreceptor system in humans. The Journal
of physiology, 535(1), 261-267.
Thompson, C., Franey, C., Arendt, J., & Checkley, S. (1988). A comparison of melatonin
secretion in depressed patients and normal subjects. The British Journal of Psychiatry,
152(2), 260-265.
96
Thorne, H. C., Jones, K. H., Peters, S. P., Archer, S. N., & Dijk, D.-J. (2009). Daily and
seasonal variation in the spectral composition of light exposure in humans.
Chronobiology International, 26(5), 854-866.
Tuunainen, A., Kripke, D. F., & Endo, T. (2004). Light therapy for non-seasonal depression.
Cochrane Database Syst Rev, 2.
Uher, R., Farmer, A., Maier, W., Rietschel, M., Hauser, J., Marusic, A., Mors, O., Elkin, A.,
Williamson, R. J., Schmael, C., Henigsberg, N., Perez, J., Mendlewicz, J., Janzing, J.
G. E., Zobel, A., Skibinska, M., Kozel, D., Stamp, A. S., Bajs, M., Placentino, A.,
Barreto, M., McGuffin, P., & Aitchison, K. J. (2008). Measuring depression:
comparison and integration of three scales in the GENDEP study. Psychological
Medicine, 38(2), 289-300.
Viney, T. J., Balint, K., Hillier, D., Siegert, S., Boldogkoi, Z., Enquist, L. W., Meister, M.,
Cepko, C. L., & Roska, B. (2007). Local retinal circuits of melanopsin-containing
ganglion cells identified by transsynaptic viral tracing. Current Biology, 17(11), 981-
988.
Wachtmeister, L., & Dowling, J. E. (1978). The oscillatory potentials of the mudpuppy
retina. Investigative Ophthalmology and Visual Science, 17(12), 1176-1188.
Warner, A., Jethwa, P. H., Wyse, C. A., I'Anson, H., Brameld, J. M., & Ebling, F. J. (2010).
Effects of photoperiod on daily locomotor activity, energy expenditure, and feeding
behavior in a seasonal mammal. American Journal of Physiology-Regulatory,
Integrative and Comparative Physiology, 298(5), R1409-R1416.
Warren, E. J., Allen, C. N., Brown, R. L., & Robinson, D. W. (2003). Intrinsic light responses
of retinal ganglion cells projecting to the circadian system. European Journal of
Neuroscience, 17(9), 1727-1735.
Wehr, T. A., Duncan, W. C., Sher, L., Aeschbach, D., Schwartz, P. J., Turner, E. H.,
Postolache, T. T., & Rosenthal, N. E. (2001). A circadian signal of change of season
in patients with seasonal affective disorder. Archives of General Psychiatry, 58(12),
1108-1114.
Wesner, M. F., & Tan, J. (2006). Contrast sensitivity in seasonal and nonseasonal depression.
Journal of Affective Disorders, 95(1), 19-28.
Westheimer, G. (1966). The maxwellian view. Vision Research, 6(11), 669-682.
Wilhelm, K., Mitchell, P., Slade, T., Brownhill, S., & Andrews, G. (2003). Prevalence and
correlates of DSM-IV major depression in an Australian national survey. Journal of
Affective Disorders, 75(2), 155-162.
Williams, J., Link, M., Rosenthal, N., & Terman, M. (1988). Structured Interview Guide for
the Hamilton Depression Rating Scale-Seasonal Affective Disorder Version (SIGH-
SAD). New York State Psychiatric Institute, New York.
WillyWeather. (2016). Brisbane Sunrise / Sunset Times. Retrieved 11th Dec, 2015, from
http://sunrisesunset.willyweather.com.au/qld/brisbane/brisbane.html
Winkler, D., Pjrek, E., Praschak-Rieder, N., Willeit, M., Pezawas, L., Konstantinidis, A.,
Stastny, J., & Kasper, S. (2005). Actigraphy in patients with seasonal affective
disorder and healthy control subjects treated with light therapy. Biological Psychiatry,
58(4), 331-336.
Wirz-Justice, A. (2006). Biological rhythm disturbances in mood disorders. International
Clinical Psychopharmacology, 21, S11-S15.
Wirz-Justice, A., Graw, P., Kräuchi, K., Gisin, B., Jochum, A., Arendt, J., Fisch, H.-U.,
Buddeberg, C., & Pöldinger, W. (1993). Light therapy in seasonal affective disorder is
independent of time of day or circadian phase. Archives of General Psychiatry,
50(12), 929-937.
97
Wirz-Justice, A., Graw, P., Roosli, H., Glauser, G., & Fleischhauer, J. (1999). An open trial
of light therapy in hospitalised major depression. Journal of Affective Disorders,
52(1-3), 291-292.
Wong, K. Y. (2012). A retinal ganglion cell that can signal irradiance continuously for 10
hours. The Journal of neuroscience, 32(33), 11478-11485.
Wong, K. Y., Dunn, F. A., & Berson, D. M. (2005). Photoreceptor adaptation in intrinsically
photosensitive retinal ganglion cells. Neuron, 48(6), 1001-1010.
Wong, K. Y., Dunn, F. A., Graham, D. M., & Berson, D. M. (2007). Synaptic influences on
rat ganglion-cell photoreceptors. The Journal of physiology, 582(1), 279-296.
Workman, J. L., Manny, N., Walton, J. C., & Nelson, R. J. (2011). Short day lengths alter
stress and depressive-like responses, and hippocampal morphology in Siberian
hamsters. Hormones and Behavior, 60(5), 520-528.
World Health Organization. (2008). The global burden of disease: 2004 Update. Geneva:
WHO Press.
Yamada, N., Martin-Iverson, M. T., Daimon, K., Tsujimoto, T., & Takahashi, S. (1995).
Clinical and chronobiological effects of light therapy on nonseasonal affective
disorders. Biological Psychiatry, 37(12), 866-873.
Young, R. S., & Kimura, E. (2008). Pupillary correlates of light-evoked melanopsin activity
in humans. Vision Research, 48(7), 862-871.
Zavada, A., Gordijn, M. C., Beersma, D. G., Daan, S., & Roenneberg, T. (2005). Comparison
of the Munich Chronotype Questionnaire with the Horne‐Östberg's morningness‐eveningness score. Chronobiology International, 22(2), 267-278.
Zele, A. J., Feigl, B., Smith, S. S., & Markwell, E. L. (2011). The circadian response of
intrinsically photosensitive retinal ganglion cells. PloS One, 6(3).
98
APPENDICES
This chapter includes the participant’s individual pupil light reflex in response to short
wavelength (blue) and long wavelength (red) light stimuli and the tools that were used for
psychological and light exposure assessment.
99
1.0 THE PUPIL LIGHT RESPONSE IN DEPRESSION AND CONTROL
GROUPS
3 0
4 0
5 0
6 0
7 0
8 0
9 0
1 0 0
1 1 0
3 0
4 0
5 0
6 0
7 0
8 0
9 0
1 0 0
1 1 0
3 0
4 0
5 0
6 0
7 0
8 0
9 0
1 0 0
1 1 0
-1 0 0 1 0 2 0 3 0 4 0
3 0
4 0
5 0
6 0
7 0
8 0
9 0
1 0 0
1 1 0
-1 0 0 1 0 2 0 3 0 4 0
Pu
pil
dia
me
ter
(% b
as
eli
ne
)
T im e (s )
Individual pupil light reflex traces in patients with (n = 8). The mean pupil light reflex
traces in response to 1 s (black rectangle) long wavelength (red) and short wavelength (blue)
light stimuli in patients with depression. The blue and red lines show the mean of the repeats
with blue and red light stimuli respectively. The vertical line denotes 6-second PIPR
amplitude.
100
3 0
4 0
5 0
6 0
7 0
8 0
9 0
1 0 0
1 1 0
3 0
4 0
5 0
6 0
7 0
8 0
9 0
1 0 0
1 1 0
3 0
4 0
5 0
6 0
7 0
8 0
9 0
1 0 0
1 1 0
-1 0 0 1 0 2 0 3 0 4 0 -1 0 0 1 0 2 0 3 0 4 0 -1 0 0 1 0 2 0 3 0 4 0
-1 0 0 1 0 2 0 3 0 4 0
3 0
4 0
5 0
6 0
7 0
8 0
9 0
1 0 0
1 1 0
Pu
pil
dia
me
ter (
% b
as
eli
ne
)
T im e ( s )
T im e ( s )
Individual pupil light reflex traces in control group (n = 13). The mean pupil light reflex
traces in response to 1 s (black rectangle) long wavelength (red) and short wavelength (blue)
light stimuli in control group. The blue and red lines show the mean of the repeats with blue
and red light stimuli respectively. The vertical line denotes 6-second PIPR amplitude.
101
2.0 THE MINI INTERNATIONAL NEUROPSYCHIATRIC INTERVIEW
(MINI_6)
halla
Due to publisher's copyright policy, the MINI International Neuropsychiatric Interview (MINI 6) cannot be made available here. For further information, please view the publisher's website at: https://medical-outcomes.com/
132
3.0 THE HAMILTON DEPRESSION RATING SCALE -SEASONAL
AFFECTIVE DISORDER VERSION (HDRS-SAD)
133
134
135
136
137
4.0 THE BECK DEPRESSION INVENTORY (BDI-II)
138
139
5.0 THE BECK ANXIETY INVENTORY
140
6.0 THE SEASONAL PATTERN ASSESSMENT QUESTIONNAIRE
(SPAQ)
141
142
7.0 THE SEASONALITY ASSESSMENT FORM (SAF)
143
8.0 THE SLEEP CHART
144
9.0 DEBRIEFING PROTOCOL
145
10.0 ACTIGRAPH SLEEP MACRO
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