2019.05.03.

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Judit Rosta

15 April 2019

Vision:CellPress-Thevisualpathwayofzebrafish

THE VISUAL SYSTEM II.

Topics nr. 72.73.

Nr. 72. Protection of the eye, image formation, refraction errors. The

function of the photoreceptors, retinal signal processing. The visual field

and the visual pathways.

Nr. 73. The visual system: the control of eye movements. Cerebrocortical

mechanisms. Binocular vision, color vision.

THE VISUAL SYSTEM I-II.

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Nr. 72. Protection of the eye, image formation, refraction errors. The

function of the photoreceptors, retinal signal processing. The visual field

and the visual pathways.

Nr. 73. The visual system: the control of eye movements. Cerebrocortical

mechanisms. Binocular vision, color vision.

THE VISUAL SYSTEM I-II.

THE VISUAL SYSTEM I.

structure of the eye

tear secretion

palpebral (cornea)-reflexes

optical power, focal point,

myopia, hyperopia, presbyopia,

astigmatism;

accomodation

intraocular pressure- glaucoma

eye movements

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STRUCURE OF THE EYE REPEAT- Visual System I.

Cataract: is a clouding of the lens

Astigmatism

Glaucoma

musc.ciliares

Accomodation

zonula fibers

(suspensory ligaments)

Aqueous Humour: a CSF-like fluid secreted from

the ciliary epithelium

drainage

rate=>intraocular

pressure

ciliary body:Accomodation

Optical Power

Pupillary Light Reaction

musc.sphincter/dilatator pupillae

pupil

1. Musc.ciliares contraction

(ggl. ciliare, pterygopalatine ggl.)

2. Zonula fibers relaxed (suspensory ligaments)-passive

3. Lens curved due to its own elasticity

ACCOMODATION

Musc.ciliaresZonula fibers

Musc.dilat.pupillMusc.dilat.pupill.

Accomodation: Parasympathetic reflex

+ musc. sphincter pupillae contraction (ggl. ciliare)

+ medial rotation of eyeballs

Ciliary body

REPEAT- Visual System I.

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THE VISUAL SYSTEM II.

pupillary light reflex

visual acuity

cell types of the human retina

phototransduction, scotopic-photopic vision

color vision

adaptation

perimetry

visual field

visual cortex

PUPILLARY LIGHT REFLEX

PUPILLARY LIGHT REFLEX (PLR)= contraction of musc.sphincter/dilatator pupillae

controls the diameter of the pupil in response to the intensity of ligh

musc.sphincter-miosis pupillae musc.dilatator-mydriasis pupillae

Atropin (muscarinergic antagonist)Parasympathetic tone

amphetamines,

LSD, ecstasy,

cocaine

Mydriatics

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Upper BRAIN STEM MOTOR

REFLEXES

PLRaff.

eff.

PALPEBRAL vs. PUPILLARY LIGHT REFLEX Visual System I.-II.

Pretectal Nucl. Nucl. Edinger-

Westphal

Consensual Reaction

Ggl. ciliare psy.

Retina

Musc.sphincter pup.

LIGHT

MYOSIS

anaesthesia, brain death

Upper BRAIN STEM MOTOR

REFLEXES

PLR

Cornea-

reflex

VOR

aff.

eff.

aff.

eff.

aff.

PALPEBRAL vs. PUPILLARY LIGHT REFLEX

PALPEBRAL-CORNEA REFLEX= closing of the eyelid elicited by stimulation of the cornea

Visual System I.-II.

Pretectal Nucl. Nucl. Edinger-

Westphal

Consensual Reaction

Ggl. ciliare psy.

Retina

Musc.sphincter pup.

LIGHT

MYOSIS

(Vestibulo-Ocular Reflex)

Cornea Trigeminal

Sensory Nucl.

Facial Motor Nucl.

Lemn.Med.

orbicularis oculi musc.Eyelidclosing

stimulus

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VISUAL ACUITY

the degree to which an optical system converges or diverges light: optical power

(unit: Dioptre)

ability to resolve fine details: spatial resolving capactiy

(unit: Visual Angle (α in: °) - human eye: one minute of arc (1'))

1°=60'Two point

distance

1/360th of a circle=1° degree of arc

spatial resolving capacity of the human eye as a function of the viewing distance:

visual acuity

(unit: Visus)

Viewing distance

object

WHAT DOES α=1 minute of arc MEAN?

Visual Angle

„critical distance”

Two point distance: 6.052 000 m

Viewing distance: 261. 109 m

Visual Angle: α=2°

VISUAL ACUITY VISUAL ANGLE: independent from viewing distance

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1,5 mm

1°

0,1 mmα

1°

Distance of viewing

(5 m/20 feet)

(25 cm)

Two-point distance

VISUAL ACUITY HOW TO CHECK VISUAL ACUITY?

SNELLEN CHART

a human eye is able to separate contours that are 1,5 mm apart from 5 m

a human eye is able to separate contours that are 0,1mm apart from 25 cm

α: independent from viewing distance

CSAPODY READING CHART

NORMAL VISUS V=5/5 (20/20) dD

Normal

5/50

5/9

5/2

D

decreased visual acuity: V<1

myopia, retinitis pigmentosa, diabetic retinopathy- far

presbyopia, cataracts- near

subject

Normal

Normal

d

VISUAL ACUITY WHAT DOES 5/2 VISION MEAN?

the distance

you are away normal sight

Dioptre Measure 20/20 Measure

-1.00 20/40

-2.00 20/80

-3.00 20/150

-4.00 20/300

-5.00 20/400

-6.00 20/500

Standard-testing distance

changeable- normal distance

V=

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SENSATION OF L(S)IGHT

The Visible Light

the basis for distinguishing among the wavelength differencies

associated with color differencies

Electromagnetic radiation:

elementary particles – PHOTONS -

propagating through space, carrying energy;

it includes: visible light= having wavelength

in the range of 400–700 nanometres

SENSATION OF L(S)IGHT Visible Light

Prism: dispersing beam of white light

The longer wavelengths (red) and the shorter

wavelengths (blue) are separated

the distance over which the wave's shape repeats

Wavelength

400-700 nm

(4-7 * 10-7 m)

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ABSORPTION

REFLECTION

REFRACTION

Light

How light energy (photon) be converted to electrical signal

(action potential)?

PHOTOTRANSDUCTION

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Photon (elementary particle of lights) can

be absorbed by molecules, provoking

modification of their structure

RETINAL

PHOTOPIGMENTS

photo-sensitive transmembrane proteins; eg. Rhodopsin

retinalretinal

opsinopsin

Retinal + Opsin

All-trans retinol (vitamin A)

SENSATION OF L(S)IGHT Photopigments

Stimulates G-protein

TRANSDUCIN

localized in

PHOTORECEPTORS

outer segment

PHOTOTRANSDUCTION

Guyton and Hall Textbook of Medical Physiology

DARK LIGHT

CGMP high

Transmitter-release (glu)

DARK CURRENTDARK CURRENT

CGMP low

LIGHT: „switching photoreceptors off”

1. Light is absorbed by photopigments

2. Photopigments are decomposed- bleached

3. „switching photoreceptors off”

Closing cGMP-gated cation channels

Hyperpolarization

Decreased Transmitter Release

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PHOTOTRANSDUCTION

How light energy (photon) be converted to electrical signal (action

potential)?

PHOTOTRANSDUCTION Cell Types of the Human Retina

Photoreceptors

Bipolar cells

Amacrine cells

Ganglion cells

Retinal epithelium

Horizontal cells

Transcriptional regulation of photoreceptor development and homeostasis in the mammalian retina;Anand Swaroop, Douglas Kim & Douglas Forrest; Nature Reviews Neuroscience 11, 563-576 (August 2010)

Dir

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Dir

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the

the

lig

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lig

ht

Sig

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Sig

nal

tran

sdu

ction

tran

sdu

ction

melanin(-albino)photopigment

regeneration

Dir

ecti

on

Dir

ecti

on

of

of

the

the

lig

ht

lig

ht

Photoreceptors: R-rods,C-cone

Inhibitory interneurons

Integrate andregulate input

from receptor cells

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SIGNAL TRANSDUCTION Photoreceptors

BIPOLARBIPOLAR

GANGLIONGANGLION GANGLIONGANGLION

BIPOLARBIPOLAR

CONVERGENCECONVERGENCE

RODSRODS

NO CONVERGENCENO CONVERGENCE

CONES in CONES in foveafovea

„on” response (depolarisation)„off” response (hyperpolarisation)

Receptive field (centrum-periphery)action potential generation

Vol. 13, No. 1 of the Creation Ex Nihilo Technical Journal,Gurney P. 1999

verted retina(invertebrates)

inverted retina(vertebrates)

PHOTORECEPTORS Retinal Distribution

0

Fovea (Foveola): only cones

foveafovea

(from Curcio et al.,1990)

CONES

RODS

peripheryperiphery

„sharp

central v

ision”

deflection of retinal cells

light reaches without distorsion

120 million

different roles and distribution

Rods and Cones

"scotopic vision„

dim light

"photopic vision„

day light6 million

Un

ive

rs. d

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RodsRods

ConesCones

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OPTIC NERVE HEAD

MACULA LUTEA

FOVEA CENTRALIS

OPTHALMOSCOPIC VIEW OPTHALMOSCOPIC VIEW RetinalRetinal vesselsvessels

No No receptorsreceptors

Sharp Sharp visionvision

HUMAN RETINAHUMAN RETINA

conescones

Chromatic and luminance properties

�1. cones and rods have different light-sensitivity (luminancy)

� 2. Spectral sensitivity: depends on photopigment-content (chroma-color)

the basis for distinguishing among the wavelength differencies associated with

color differencies

PHOTORECEPTORS COLOR VISION

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Photorpigments with different absorption spectrum

Rods: Rhodopsin

Cones: 3 different photopigments

PHOTORECEPTORS COLOR VISION

Color Vision Anomalies

how the three cone types

are arranged in the fovea

CONE MOSAIC

Ishihara-color test (Practice!)

• altered spectral sensitivity of one type of cones/

• total absence of function of one cone type/ etc. lack of green

• one type of pigment can be found= total color blindness

red-, green-, blue- sensitive cones

the ability of the photoreceptors to adjust to various

levels of darkness and light

the sensitivity of the retina decreases

when light intensity increases

LIGHT ADAPTATION DARK ADAPTATION

the sensitivity of the retina increases

when light intensity decreases

PHOTORECEPTORS ADAPTATION

1. pupil dilatation

2. low light intensity: not enough for cones

3. rods photopigments are decomposed

during light, re-built slowly (30 min)

1. pupil constrict

2. high light intensity: rods are quickly

saturated

3. „cone-switch”

Photopigments regeneration- cones quick (2-3 min), rods slow (30min)

avoiding saturation (= photoreceptor

become insensitive)

Bleaching: the light is absorbed by the photopigment- photopigments are decomposed

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The Visual Pathway

Extrageniculate projections

Pretectum:

Pupillary Light Reflex

Pathway

Guyton and Hall. Medical Phys.

optic nerve fibers from the nasal halves of

the retinas cross to the opposite sides

visual hemifields on the retina!

temporal hemifield � nasal retina � opposite prim.visual cortex

Te

mp

ora

l he

mifie

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l he

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ld

PERIMETRY TEST: mapping of the visual field

Visual Field

OPTHALMOMETRY: measures biometrical differencies in the

structures of eye (i. e. curvature of the cornea)

Javal-Schiötz Ophthalmometer

130°-145°

Binocular Visual Field

Monocular Visual Field

physiological scotoma (blind spot).

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The Visual Pathway

MAGNOCELLULAR

pathway

PARVOCELLULAR

pathway

Visual informations become segregated

in the visual pathway

Lateral Geniculate Nucleus (CGL)

color sensation sensitivity to temporal frequency

Retina

striatal-stripes

Magnocellular Parvocellular

Processing of Information in the Visual Cortex

Functional Unit of the

Primer Visual Cortex: „Columna”

3232

ORIENTATION COLUMNSORIENTATION COLUMNS

Color-sensitive blobs

neurons respond to stimuli

oriented at the same angle

input from CGL

becomes

segregated into

monocular regions

Primer Visual Cortex V1

(Hubel & Wiesel, 1958)

OCULAR OCULAR

DOMINANCE DOMINANCE

COLUMNSCOLUMNS

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V2: recognition of complex forms

V3: geometry

V3a: movement-direction

V4: color

V5: kinetic-(movement)

V6: stereopsis

Association cortical areas

Temporal lobe

(„inferotemporal cortex”):

shape-and form

Processing of Information in the Visual Cortex

Coordination of eye movements

Extragenicular projections

C. Colliculus Superior:

coordinating of eye movements

OPTOKINETIC

NYSTAGMUS in

response to the

movement of visual

field images

B. Pretectalis Area:

I. pupillary light reflex

II. accomodation reflex

III. optokinetic reflex

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Coordination of eye movements

Classification of eye movements

based on the relationship of the optical axis:

I. conjugated eye movement

II. converging, diverging movements

III. torsion movements

based on speed:

I. pursuit movements < 60 °/s

if object, head or body moves

II. saccads: < 60 °/s up to 1000 °/s

short and fast with or without head

movements

III. fixation periods (max. 0,5 s duration)torsion

1sec

PERCEPTION Stereopsis

Stereopsis: 3D perception „depth perception” (distance)

information about depth

Disparity=difference

BINOCULAR DISPARITY

Retinal localization

Corresponding retinapoints: the two retina identical

points when the retinas are overlapped; Fixed object is

mapped on corresponding points of the two retina

Horopter: imaginary surface

whose points are all at the same

distance as the fixation point

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Difference between X and y code depth information

Non-corresponding retinal pointsCorresponding retinal points

Stereopsis

Retinal localization- information about depth (distance)

� embedded with microelectric sensor

� Presbyopia, glucose monitoring, anti-allergic drugs

(Johnson & Johnson Vision Care’s; 2017)

„Smart Contact Lens”

2014, a University of Michigan: contact lens for

„night vision”

Review of optometry (published Febr, 2017)