MICROSCOPIC MICROSCOPIC STRUCTURE OF STRUCTURE OF

RETINARETINA

DR.PARESH VARSAT

RETINA UNIT

MICROSCOPIC STRUCTURES OF RETINA:

Retina consists of 10 layers from outward to inwards:0 1.Retinal pig epithelium0 2.Layer of rods & cones0 3.Ext limiting memb0 4.Outer nuclear layer0 5.Outer plexiform layer0 6.Inner nucler layer0 7.Inner plexiform layer0 8.Ganglion cell layer 0 9.Nerve fibre layer 0 10.Internal limiting

membrane

Retinal Pigment Epithelium:0 Outermost layer of retina 0 It consists of a single layer of hexagonal shaped

cells containing pig.0 Responsible for granular appearance of fundus 0 RPE is firmly adherant to bruch’s memb.&loosely

attached to layer of rods & cones 0 The potential space b/w RPE & sensory retina is

called subretinal space0 In retinal detachment fluid collection in this

space is called subretinal fluid

Functions Of RPE0Photoreceptor renewal & recycling of vitamin A0Maintains inegrity of subretinal space by forming

outer blood retinal barrier & actively pumping ions & water out of it

0Transport of nutrients & metabolites through the blood retinal barrier

0RPE cells have phagocytic action 0Mechanical support to the processes of

photoreceptors.0Manufactures pig.which has optical function in

absorbing light

Layer Of Rods & Cones :(photoreceptor cell layer)0 Rods & Cones are the end organs of vision which transform

light energy into visual impulse 0 Rods contain a photosensitive subs. Visual purple

(rhodopsin)& subserve the peripheral vision & vision of low illumination(scotopic vision)

0 Cones contain a photosensitive substance(iodopsin) & responsible for highly descriminatory central vision (photopic vision) & colour.

0 There are abt. 120 million rods & 6.5 million cones 0 The highest density of cones is at fovea & their no. reduces

outside fovea0 Rods are absent at the fovea in an area of 0.35mm &

maximum below the optic disc, their no. reduces towards the periphery

Structure Of Photorecptor

1)Cell body2)Nucleus (outer nuclear layer)3)Cell processes (outer plexiform layer)4)Outer and inner segments (upto external limiting membrane)

External Limiting Membrane:

0 fenestrated membrane extends from the ora serrata to the edge of the optic disc through which pass processes of the rods & cones

0 Formed by the junctions b/w the cell membrane of photorecptors & muller’s cell

Outer Nuclear Layer:

0 Formed by the nuclei of rods & cones0 Cone nuclei are larger than rod nuclei & lie in a single

layer next to the internal limiting membrane0 Rod nuclei form the bulk of this multilayered layer

except in the cone dominated foveal region

Region of retina Layer of nuclei Thickness(micrometer)

Nasal to Disc 8 to 9 45

Temporal to Disc 4 22

Foveal region 10 50

Rest of the retina except ora serrata

1 layer of cone4 layer of rod

27

Outer Plexiform Layer:(junction b/w end organ of vision & 1st order neuron)

0 Contains the synapses b/w the rod spherules & cone pedicles with the dendrites of the bipolar cells & processes of the horizontal cells

0 Also known as Henle’s layer (oblique fiber arranged deviated from the fovea)

Inner nuclear Layer:

0 Consist of the following-0 Bipolar cell0 Horizontal cells0 Amacrine cells0 Muller’s cells0 Capillaries of the central retinal vessels

1)Bipolar cells0 Neurons of first order of vision0 The body of the bipolar cells consists entirely of the

nucleus which lies in the inner nuclear layer 0 There are nine types of bipolar cell-

2)Horizontal neurons0 These are flat cells having numerous horizontal

associative & neuronal interconntections b/w photoreceptors & bipolar cells in the outer plexiform layer

0 Two type of cell-0 Type a-seven group of dendrites have contact with

triad of seven cone pedicles and single axons has contact with distant cone triad

0 Type b-dendrites have contact with rod receptor only and axons with distant rod cell

3)Amacrine cells0 Situated within the innermost part of this layer0 Single process have connection with axons of bipolar cell

and dendrites & soma of ganglion0 Perform an integrative function similar to horizontal cells4)Muller’s cell0 The nucleus & cell bodies of the cells are located within the

inner nucler layer0 Provide structural support & contribute to the metabolisn

of the sensory retina 5)Glial cells0 astrocytes,microglia & oligodendrocytes

Inner plexiform layer:

0 Consists of synapses b/w the axons of bipolar cells, dendrites of ganglion cells & the processes of integrative amacrine cells

0 Absent at the foveola

Ganglion cell layer:(second order neuron of visual pathway)

0 The cell bodies & the nuclei of the ganglion cells lie in this layer0 It is composed of a single row of cells except in the macular

region where it is multilayered 0 Absent in the foveola Classification-1. W,X & Y ganglion cell2. P & M ganglion cell3. Monosynaptic(central retina) & poly synaptic

ganglion(peripheral retina)

Nerve fibre layer:

0 Consist of the unmyelinated axon of the ganglion cells(centripetal nereve fiber) which converge at the optic nerve head,pass though lamina cribrosa

0 This layer also contains - Centrifugal nerve fibres Processes of muller’s cells Neuroglial cells 0 Rich bed of superficial capillary network is present

in this layer

Arrangements of nerve fibers in Retina & Optic disc & Thickness

Internal limiting membrane 0 Consists of a PAS positive true basement membrane

that forms interface b/w retina & vitreous 0 consist of 4 elements - 1) collagen fibrils 2) proteoglycans of vitreous 3) basement membrane 4) plasma membrane of muller cells

0 In this area, there are no rods.0 Cones are tightly packed and other layers of retina are

very thin.0 Its central part (foveola) largely consists of cones and

their nuclei covered by a thin internal limiting membrane.

0 All other retinal layers are absent in this region.0 In the foveal region surrounding the foveola, the cone

axons are arranged obliquely (Henle’s layer or outer plexiform layer) to reach the margin of the fovea

Structure of fovea centralis:

Fovea centralis:

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