Seminar on Assessment of Visual field.Seminar on Assessment of Visual field.

Automated Perimetry.Automated Perimetry.

Moderator - Prof. H.Ashraf.Moderator - Prof. H.Ashraf.

Presenter - Dr. Ricky Mittal.Presenter - Dr. Ricky Mittal.

25/08/0925/08/09 Saifi HallSaifi Hall..

What is the normal visual field?

Traquair-“island of vision Traquair-“island of vision surrounded by the sea of surrounded by the sea of darkness.”darkness.”

3 dimensional- strategies that 3 dimensional- strategies that are the foundation of all are the foundation of all perimetric examinations.perimetric examinations.

X-Y axis, Z axis.X-Y axis, Z axis. Kinetic perimetry:Kinetic perimetry: extent along X-Y axis.extent along X-Y axis. Static perimetry: differential Static perimetry: differential

light sensitivity ,altitude of light sensitivity ,altitude of the hill of vision along the hill of vision along vertical z axis.vertical z axis.

Extent of visual field, XY axis:Extent of visual field, XY axis:

Basic terminologiesBasic terminologies:: Threshold :: Physiological capacity to detect a stimulus at a given Physiological capacity to detect a stimulus at a given

location, that stimulus intensity that has a 50%probability of location, that stimulus intensity that has a 50%probability of being seen.being seen.

Apostilbs: : Absolute units of light intensity.Absolute units of light intensity. Luminance of test target.Luminance of test target. 1 asb=.3183 candela/m1 asb=.3183 candela/m22

Decibels: : Relative scale, created by manufacturers. Relative scale, created by manufacturers. Attenuation of light by neutral density filters.Attenuation of light by neutral density filters. 1dB=1/10 log units of attenuation of max. stimulus.1dB=1/10 log units of attenuation of max. stimulus. Measures sensitivity at each point.0to40dB.Measures sensitivity at each point.0to40dB.

Sensitivity Vs threshold:Sensitivity Vs threshold:

Inverse relationship.Inverse relationship.

In automated perimetry, threshold is recorded in the inverted In automated perimetry, threshold is recorded in the inverted decibel scale, and dimmer targets have higher decibel decibel scale, and dimmer targets have higher decibel values.values.

Therefore, threshold in Therefore, threshold in decibelsdecibels is directly proprotional to is directly proprotional to retinal sensitivityretinal sensitivity..

Apostilbs Vs decibelsApostilbs Vs decibels::

Lumininance of test targets is measured in an absolute unit, Lumininance of test targets is measured in an absolute unit, apostilbs.apostilbs.

Decibel is a relative scale created by manufacturers of Decibel is a relative scale created by manufacturers of automated perimeters to measure sensitivity.automated perimeters to measure sensitivity.

Inverted logarithmic scale with 0dB=brightest stimulus. Not Inverted logarithmic scale with 0dB=brightest stimulus. Not standardized.standardized.

Total deviation :difference between patient’s threshold measured :difference between patient’s threshold measured and value expected in age matched normals.and value expected in age matched normals.

Global indicesGlobal indices::

Mean deviation: mean difference between : mean difference between sensitivities of age matched normals and subject.sensitivities of age matched normals and subject.

Highlights overall depression, dB, STATPAC, p Highlights overall depression, dB, STATPAC, p value.value.

Indicated as:Indicated as: -ve in Humphrey.-ve in Humphrey. +ve in Octopus.+ve in Octopus. Pattern standard deviation: this is a measure of : this is a measure of

degree to which the shape of patients field differ degree to which the shape of patients field differ from normal, extent of focal loss as a single value.from normal, extent of focal loss as a single value.

PSD can be normal when there is a diffuse loss.PSD can be normal when there is a diffuse loss.

primarily reflects retinal condition.primarily reflects retinal condition. excludes conditions affecting the overall field.excludes conditions affecting the overall field. PSD:PSD: small value-normal field or diffuse loss.small value-normal field or diffuse loss. scotoma -clearly abnormal.scotoma -clearly abnormal. advanced -PSD starts decreasing if many threshold values near advanced -PSD starts decreasing if many threshold values near

0dB.0dB.

SF: Intratest test variability, threshold at 10 predetermined points, : Intratest test variability, threshold at 10 predetermined points, twice.twice.

SD – SFSD – SF indicator of patient’s consistency, pathology.indicator of patient’s consistency, pathology. 1-2.5dB.1-2.5dB.

CPSD: extent of focal loss in the visual field, taking short term : extent of focal loss in the visual field, taking short term fluctuations in account i.e. which is not caused by SF.fluctuations in account i.e. which is not caused by SF.

Probability analyses:: symbolic represenation.symbolic represenation. Statistical probability of a threshold value measured at a point that Statistical probability of a threshold value measured at a point that

exists in age-matched normals.exists in age-matched normals. Darker the symbol lower the probability.Darker the symbol lower the probability. Comparison on a point by point basis.Comparison on a point by point basis. Cataract, ref.error excluded.Cataract, ref.error excluded. Retinal condition.Retinal condition.

Glaucoma hemifield test:Glaucoma hemifield test: Compares five zones (along Compares five zones (along

the nerve fibre bundles) in the nerve fibre bundles) in the upper field with their the upper field with their mirror images in the lower mirror images in the lower field.field.

A very good determinant of A very good determinant of the presence of glaucomatous the presence of glaucomatous damage on a single field.damage on a single field.

Does not analyze temporal Does not analyze temporal nerve fibre bundle defects.nerve fibre bundle defects.

Inference:Inference: Outside normal limits.Outside normal limits. <1%,0.5%.<1%,0.5%. Borderline.Borderline. 3%3% Abnormally low sensitivity.Abnormally low sensitivity. 5%5% Abnormal high sensitivity.Abnormal high sensitivity. higher than 99.5%higher than 99.5%Within normal limits.Within normal limits.

Basics of the Humphrey field Basics of the Humphrey field analyser:analyser:

Projection type automated static Projection type automated static perimeter.perimeter.

Most popular, consistency of basic Most popular, consistency of basic hardware,hardware,

constant upgradation of the software on constant upgradation of the software on the basis of clinical feedback from the the basis of clinical feedback from the ophthalmologists.ophthalmologists.

The machine:The machine:Viewing distance-33cms.Viewing distance-33cms.Background illumination-31.5asb.Background illumination-31.5asb.Static mode, newer models - kinetic.Static mode, newer models - kinetic.

Stimulus size: Stimulus size: Goldman stimulus Goldman stimulus size(1to5)size(1to5)

Stimulus duration:0.2 Stimulus duration:0.2 second.second.

Fixation monitor: : Heijl Krakau blind Heijl Krakau blind spot technique, gaze spot technique, gaze monitoring.monitoring.

Data storage.Data storage. STATPAC: computerised statistical packageSTATPAC: computerised statistical package Comparison of patients results with age matched normal Comparison of patients results with age matched normal

data.data. Patients own baseline with follow up data.Patients own baseline with follow up data. Newer HFA series: database of stable glaucoma patients for Newer HFA series: database of stable glaucoma patients for

glaucoma change probability analysis.glaucoma change probability analysis.

Interpretation of visual field:Interpretation of visual field:

Recognise artifacts:

Reliability.

Assessment of damage..

Baseline visual field examBaseline visual field exam:: 2 fields – min. baseline.2 fields – min. baseline. 11stst field-Central 30-2 threshold field-Central 30-2 threshold 22ndnd -central 30-2 threshold within 1 to 2 months. -central 30-2 threshold within 1 to 2 months.

Provided:Provided: Consistent ,no learning effect.Consistent ,no learning effect. <2dB (MD).<2dB (MD).

If 1If 1stst field constricted or depressed: field constricted or depressed: Obtain 10-2 threshold test.Obtain 10-2 threshold test. Retest with size5 stimulus(64mmRetest with size5 stimulus(64mm22).). Or combine.Or combine.

ArtifactsArtifacts

Lid.Lid. Lens rim-too far or the eye is not centered.Lens rim-too far or the eye is not centered. Refractive error.Refractive error. Learning effect.Learning effect. Pupillary size.Pupillary size. Rapid fatigue.Rapid fatigue.

Reliability:Reliability:

FalseFalse positives-tendency of the patient to press the positives-tendency of the patient to press the trigger not in response to seeing a stimulus but at trigger not in response to seeing a stimulus but at random, either as a response to an audible cue or random, either as a response to an audible cue or due to the expectation of the stimulus.due to the expectation of the stimulus.

Ratio of such responses to the number of FP catch Ratio of such responses to the number of FP catch trials done.trials done.

>33%FP rate is flagged with a double XX.>33%FP rate is flagged with a double XX. Low reliability.Low reliability.

False negativeFalse negative::

False negative responses are failure of the patient to False negative responses are failure of the patient to respond to stimulus 9 dB more intense than the previously respond to stimulus 9 dB more intense than the previously determined threshold at that point due to patient inattention determined threshold at that point due to patient inattention or fatigue.or fatigue.

Reason may be a tired patient.Reason may be a tired patient. A high FN rate may or may not be reliable.A high FN rate may or may not be reliable. Cloverleaf defect due to high FN.Cloverleaf defect due to high FN.

Fixation losses:Fixation losses:

Not all fixation losses represent true loss of fixation.Not all fixation losses represent true loss of fixation. High fixation loss may indicate, centre of blind spot was High fixation loss may indicate, centre of blind spot was

slightly mislocated.slightly mislocated. If FP, FN rates and STF are low, then the high FL can be If FP, FN rates and STF are low, then the high FL can be

discounted.discounted. If two baseline fields are similar it can again be discounted.If two baseline fields are similar it can again be discounted. Mislocation of the blind spot.Mislocation of the blind spot. Macular disease.Macular disease.

Short term fluctuations:Short term fluctuations:

Testing option, shows variability of patients response over a Testing option, shows variability of patients response over a single test period.single test period.

low (low (≤2dB) SF- good reproducibilty ≤2dB) SF- good reproducibilty

high (≥ 3dB) SF-poor reproducibilityhigh (≥ 3dB) SF-poor reproducibility

Minimum Criteria for Diagnosing Minimum Criteria for Diagnosing Acquired GlaucomaAcquired Glaucoma::

A Glaucoma Hemifield Test outside normal limits on at least A Glaucoma Hemifield Test outside normal limits on at least two fields.two fields.

oror

A cluster of three or more non edge points in a location A cluster of three or more non edge points in a location typical for glaucoma, all of which are depressed on the PD typical for glaucoma, all of which are depressed on the PD plot at pplot at p<5% level and one of which is depressed at p <5% level and one of which is depressed at p <1%level on two consecutive fields.<1%level on two consecutive fields.

oror A CPSD that occurs in less than <5% of normal fields on two A CPSD that occurs in less than <5% of normal fields on two

consecutive fields.consecutive fields.

Early defect:: Neither extensive nor near fixation.Neither extensive nor near fixation. Mean deviation index (MD) –better than Mean deviation index (MD) –better than -6dB.-6dB. On PD plot:On PD plot: 1.<25%(18) points are below 5% level. 1.<25%(18) points are below 5% level. 2.< 10 points below 1% level.2.< 10 points below 1% level. Central 5°-no points having less than 15dB sensitivity.Central 5°-no points having less than 15dB sensitivity.

Moderate defect:: MD<-12dB.MD<-12dB. 1.PD-<50%( 37) points 1.PD-<50%( 37) points << 5% and < 20 points 5% and < 20 points <1%.<1%. Central 5°-no points with 0dB.Central 5°-no points with 0dB. Only one hemifield Only one hemifield may havemay have a point in central 5° with a point in central 5° with

<15dB sensitivity.<15dB sensitivity.

Severe defect:: Any of the following:Any of the following: 1.MD plot 1.MD plot >-12dB>-12dB 2.PDplot:2.PDplot: >37 points depressed below<5%.>37 points depressed below<5%. >20 points depressed below 1%.>20 points depressed below 1%. Any point in central 5°has sensitivity of 0dB.Any point in central 5°has sensitivity of 0dB. Central 5°-points <15dB in both hemispheresCentral 5°-points <15dB in both hemispheres..

Recognition of progressive damageRecognition of progressive damage::

1.new defect.1.new defect. 2.deepening of pre exisiting defect.2.deepening of pre exisiting defect. 3.expansion of pre existing defect.3.expansion of pre existing defect. 4.entire field develops decreased sensitivity.4.entire field develops decreased sensitivity.

How would u approachHow would u approach??

Compare baseline field to each individual fieldCompare baseline field to each individual field

Study the entire series.Study the entire series.

Compare with baseline fieldCompare with baseline field:: 1.For a new defect in previously normal area1.For a new defect in previously normal area.. Cluster of 3 or or more non edge points eachCluster of 3 or or more non edge points eachof which declines by 5 or >5dB.of which declines by 5 or >5dB. 2.For deepening of pre existing defect2.For deepening of pre existing defect.. A cluster of 3 or more non edge points, each of which declines A cluster of 3 or more non edge points, each of which declines

by 10 or>10dB.by 10 or>10dB. 3.Generalized depression3.Generalized depression::Decline of all points by 3dB.Decline of all points by 3dB.

Glaucoma change probability programme:Glaucoma change probability programme:

Point by point probability of any change in baseline field Point by point probability of any change in baseline field and new field.and new field.

1.new defect: 3 or more non-edge points each of which, : 3 or more non-edge points each of which, p<5%,on two consecutive fields.p<5%,on two consecutive fields.

2.deepening of pre existing defect: part of a scotoma, : part of a scotoma, cluster, p<5%.cluster, p<5%.

3.3.expansion:: Within 15Within 15° of field-2 previous normal points.° of field-2 previous normal points. Outside 15° of field-3 previously normal points depressed Outside 15° of field-3 previously normal points depressed

with p,5%.with p,5%.

Generalized depressionGeneralized depression:: Decline in MD, p<1%.Decline in MD, p<1%.

ReferencesReferences::

Illustrated Automated Static Perimetry G.R.Reddy.Illustrated Automated Static Perimetry G.R.Reddy. Testing of the Field of Vision-Douglas R.Anderson.Testing of the Field of Vision-Douglas R.Anderson. Clinical Decisions in Glaucoma-Elizabeth Hodapp,Richard Clinical Decisions in Glaucoma-Elizabeth Hodapp,Richard

K.Parrish,Doughlas R.Anderson.K.Parrish,Doughlas R.Anderson. Visual Field Examination-A.K.Gupta ,Reena Visual Field Examination-A.K.Gupta ,Reena

M.Chaudhary,Charu Tandon.M.Chaudhary,Charu Tandon.

..Thank youThank you..