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RETINA


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INDEX

INTRODUCTION (AVINASH)

ANATOMY ( MANUJA)

BLOOD SUPPLY (RAKESH)

PHOTOCHEMISTRY ( SHWETHA ANDAVINASH)

PHYSIOLOGY (AVINASH)


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INTRODUCTION

Retina is multi-layered sensory tissue thatlines the back of eye.

It contains millions of photoreceptors thatcapture light rays and convert them intoelectrical impulses.

These impulses travel along the optic nerveto the brain where they are turned toimages.


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DIMENSIONS OF RETINA

2.1mm temporally , 0.7-0.8mmnasally.

The total surface area of retina is266mm square.


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OPTIC DISC

pale pink in colour, circular inshape.

photo receptors are absent.

known as Blind spot.


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MACULA

known as yellow spot.

elliptical in shape.

diameter is 5.5mm.responsible for central vision


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FOVEA

It is the most sensitive part of the Retina.

Its diameter is 1.85mm .

It has 5 degree of visual field.thickness is 0.25mm.


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ORA SERRATA

It is the last region where theretina ends and ciliary body starts.

consist of tooth like projection .

Retina is attached both to the

vitreous &retinal pigmentedepithelium.


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ANATOMY OF RETINA


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LAYERS OF RETINA

Retinal pigmented epithelium

Layers of rods and cones

External limiting membrane

Outer nuclear layer

Outer molecular layer

Inner nuclear layer

Inner molecular layer Ganglion cell layer

Nerve fibre layer

Internal limiting menbrane


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LAYERS OF RETINA

RETINAL PIGMENTED EPITHELIUM

Outermost layer

Consist of Single layer of hexagonal It is Loosely attached to the layers of rods

&cones

The potential space between RPE &the sensory

retina is called subretinal space filled withsubretinal fluia


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LAYERS OF RETINA

LAYERS OF ROD AND CONES

ROD

contains rhodopsin as a photosensitivesubstances.

helps in vision of low illumination.

120 million in number,absent in foveaCONES

helps in phototopic vision

6.5 million in number,highest in fovea


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LAYERS OF RETINA

EXTERNAL LIMITING MEMBRANE

layer that separate the inner segment

portions of the photoreceptors from their cellnucleus.

OUTER NUCLEAR LAYER

this layer contains the rod and cell bodies.

the cone cell body and nucleus are larger.


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LAYERS OF RETINA

OUTER PLEXIFORM LAYER

projections of rod and cones ending in the rod

spherule and cone pedicle respectively.

these make synapses with dendrites of bipolar

in the macular region also known as fiber layer

of henle.


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LAYERS OF RETINA

INNER NUCLEAR LAYER

consist of the cell bodies of horizontal

cells,bipolar cells,amacrine cells,interplexiformneurons.

INNER PLEXIFORM LAYER

Cointains the synapse between the bipolar cellaxon and the dendrites of the ganglion andamacrine cells.


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LAYERS OF RETINA

GANGLION CELL LAYER

contains nuclei of ganglion cells, the axonsof which become the optic nerve fibres for

messages.

NERVE FIBRE LAYER

Consist of ganglion cell axon.

INNER LIMITING MEMBRANE

Innermost boundary

Composed of muller cells.


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BLOOD SUPPLY OF RETINA

Four layers RPE,layers of rod andcones,external limiting membrane,outernuclear layer gets blood supply fromchoriocapillaries.

The rest six layers gets from central retinalartery.

Fovea is avascular but partially gets bloodsupply from choriocapillaries.

Macular area gets from central retinal artery

and cilioretinal artery.


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PHOTOCHEMISTRY OF VISION

VITAMIN A AND VISUAL PIGMENTS

dietary sources of retinol for human is animal

and plant food. animal food contains retinol but plant do

not.

carotenes in plant food is converted toretinol by metabolic activity of smallintestine.


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ABSORPTION AND STORAGE In intestine, Vit A is esterified and reaches the

blood stream. Retinol from the blood stream is transported

to the liver. Retinol becomes bound with retinol binding

protein.

The retinol protein complex enters thecirculation and reaches the target tissues In retina it becomes attached to the basal

surfaces of the RPE cells.


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VISUAL PIGMENTS

RHODOPSIN

photosensitive pigment,present in outersegment of disc of rod, contain protein

called opsin,insoluble in water,sensitive to

heat and chemical agents. PHOTOPSIN

different from rod,responsible for central

and colour vision.


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PHYSIOLOGY OF VISION

INITIATION OF VISION

PROCESSING AND TRANSMISSION OF

VISUAL SENSTAION VISUAL PERCEPTION


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INITIATION OF VISION

Also known as phototransduction.

The whole phenomenon of conversion of

light energy into nerve impulse is known asphototransduction.

Photochemical changes take place .


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RHODOPSIN BLEACHING

Rhodopsin refers to the visual pigmentpresent in the rods the receptors fornight(scotopic) vision.

Its maximum absorption spectrum is around500 nm.

Rhodopsin consists of a colourless protein

called opsin coupled with a carotenoid called

retinine


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RHODOPSIN BLEACHING

Light falling on the rods converts 11-cis-retinal componentof rhodopsin into all-trans-retinalthroughvariousstages .

The all trans-retinal so formed is soonseparated from the opsin.

This process of separation is called

photodecomposition. Rhodopsin is said to be bleached by the

action of light.


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VISUAL CYCLE

In the retina of living animals, under constantlight stimulation, a steady state must existunder which the rate at which are bleached isequal to the rate at which they areregenerated. This equilibrium between thephotodecomposition and regeneration of

visual pigmentsis referred to VISUAL CYCLE.


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