ANATOMY AND PHYSIOLOGY OF RETINA ( Part 2)[1].pptx

Anatomy of retina

1. ANATOMY AND PHYSIOLOGY OF RETINA (PART 2) Presented by :- Sayoki Ghosh

2. INTRODUCTION The retina (Latin: rete = net), in the most comprehensive sense, includes all structures that are derived from the optic vesicle (namely, the sensory layers of the retina (pars optica retinae), the pigmented epithelium of the retina), as well as the epithelial linings of the ciliary body (pars retinae ciliaris) and of the iris (pars retinae iridis). Anthony J.Bron , Ramesh C.tripathi,Brenda J.Tripathi “Wolff’s anatomy of the eye and orbit”:Eighth edition

3. GROSS ANATOMY Extent:- From optic disc to ora serrata and has a surface area of 266 mm square. Thickness:- 0.56mm(at the posterior pole in the peripapillary region) 0.18-0.2 mm ( at the equator) 0.1 mm ( at the ora serrata ) Color:- Purplish red (due to visual purple of red) After death of a person , it appears white opaque. Regions: - Grossly on ophthalmic examination , the fundus can be divided into 3 distinct regions:- Optic disc Maculae Lutea Peripheral retina A.K.Khurana. Indu Khurana “Anatomy and physiology of eye”; Modern system of ophthalmology (MSO) series; CBS Publishers and distributors.

4. MICROSCOPIC STRUCTURE OF THE RETINA Retinal pigment epithelium Layer of rods and cones External limiting membrane Outer nuclear layer Outer plexiform layer Inner nuclear layer Inner plexiform layer Ganglion cell layer Nerve fiber layer At the fovea the only layers that are present are the retinal pigment epithelium, the photoreceptors (cones only), the external limiting membrane, the outer nuclear layer (which contains the nuclei of the cone cells), the inner fibres of the photoreceptors (the so-called 'Henle's fibre ' layer), and the internal limiting membrane.

5. RETINAL PIGMENT EPITHELIUM Outermost layer of retina. Continuous brown sheet that extends from optic nerve to ora serrata . In far periphery extends as pigmented layer of cilliary epithelium. Consists of single layer of hexagonal shaped cells containing pigment. 4-6 million per RPE cells per eye. Fine mottling due to unequal pigmentation of cells → Granular appearance of fundus. Firmly adherent to underlying Bruch’s membrane(BM) of the choroid, (which has highly vascular choriocapillaries) and loosely attached to the overlying layer of rods and cones( outer segment). Sub retinal-space :- The potential space between RPE and sensory retina. CLINICAL PEARL:- The separation of RPE from sensory retina is called Retinal detachment , and the fluid between the two layers is called sub retinal fluid .

6. * Chtcheglova , Lilia & Ohlmann , Andreas & Boytsov , Danila & Hinterdorfer , Peter & Priglinger , Siegfried & Priglinger , Claudia. (2020). Nanoscopic Approach to Study the Early Stages of Epithelial to Mesenchymal Transition (EMT) of Human Retinal Pigment Epithelial (RPE) Cells In Vitro. Life. 10. 128. 10.3390/life10080128.

7. RETINAL PIGMENT EPITHELIUM: ULTRASTRUCTURE Size and Shape of the cells:- Each cell has 4-8 sides giving cobblestone appearance. Total number:- 4.2-6.1 million In the area centralis, each cell measures 12-18µ in width 10-14µin height In the periphery, cells become flatter 60µ in width With increasing age, the pigmented cells in macular region increase in height and decrease in width ; While vice versa occurs in the cells of the periphery .

8. https://entokey.com/structure-and-function-of-the-retinal-pigment-epithelium / https://entokey.com/cell-biology-of-the-retinal-pigment-epithelium /

9. RETINAL PIGMENT EPITHELIUM: ULTRASTRUCTURE Paracellular surface:- Electron microscopy shows that RPE cells are frequently separated by an optically empty space. They also show close cellular approximation. Adjacent cells joined at their lateral apical margin by terminal bars. From top to bottom these bars consist of gap junction, zonula occludens and zonula adherence . Junctional complex form BLOOD-RETINAL BARRIER(BRB). Maintains retinal homeostasis and toxic damage. Nutrients from the choriocapillaries diffuse through basal lamina and between the paracellular space up to the terminal bars, where the zona occludens form the external component of the BRB.

10. RETINAL PIGMENT EPITHELIUM: ULTRASTRUCTURE

11. RETINAL PIGMENT EPITHELIUM: ULTRASTRUCTURE Apical part:- F ormed by the microvilli projecting between rods and cones. 45 photoreceptors overlie each RPE cell. Highest concentration of melanin granules due to melanosomes. Lipofuscin, a major RPE pigment accumulates gradually with age. Function:- Absorb stray light and minimize scatter within eye. Basal part:- Have convulated infolds to increase the surface area for absorption and secretion of the material. Lies in contact with the Bruch’s membrane of the choroid.

12. FUNCTION OF RPE:- Photoreceptor renewal and recycling of vitamin A. Maintains integrity of the subretinal space. Transport of nutrients and metabolites. Phagocytic action Provides mechanical support. Regeneration and reparative function after injury and surgery. Electrical homeostasis.

13. NEUROSENSORY RETINA The neurosensory retina consist 3 types of cells and their synapses arranged in 9 layers ( inward to outward):- Layer of rods and cones External limiting membrane Outer nuclear layer Outer plexiform layer Inner nuclear layer Inner plexiform layer Ganglion cell layer Nerve fiber layer https://www.ndrs.scot.nhs.uk/? page_id=1587 A.K.Khurana. Indu Khurana “Anatomy and physiology of eye”; Modern system of ophthalmology (MSO) series; CBS Publishers and distributors.

14. LAYERS OF RODS AND CONES Also known as neuroepithelium. This layer contains outer segment of rods and cones. Flat preparation of the retina viewed by the optical or scanning electron microscopy reveals that the cells are arranged in mosaic/palisade manner. Individual variation of density of rods and cones varies.

15. LAYERS OF RODS AND CONES:- DENSITY AND DISTRIBUTION OF PHOTORECEPTORS Photoreceptors are end organs of vision which transform light energy into visual (nerve) impulse. RODS Contains photosensitive substances known as Visual purple( Rhodopsin) Subserve the peripheral vision and vision of low illumination . CONES Contains photosensitive material known as Iodopsin. Primarily responsible for highly responsible for highly discriminatory central vision (photopic vision) and color vision. Number of photoreceptors:- Rods:- 77.9 – 107.3 million ( average 92 million) Cones:- 4.08 – 5.29 million ( average 4.6 million) Distribution of rods:- Absent at fovea within an area of 0.35mm(rod free zone)≈1.25◦ of the visual field. Larger no. of rods is present in a ring shaped zone 5-6 mm from the fovea(160,000/mm sq.). Maximum below optic disc (170,000/mm sq.) . The number gradually reduces from central to periphery.

16. LAYERS OF RODS AND CONES:- DENSITY AND DISTRIBUTION OF PHOTORECEPTORS Distribution of cones:- Highest density at fovea (≈0.032◦)with an average of 19,900 cones/mm sq., but their number is highly variable and ranges from 10,000 to 32,4000 cones/mm sq. The number of cones falls off rapidly outside the fovea ; being only 6000 cones/mm sq. 3 mm away https:// www.quora.com/Do-retinal-ganglion-cells-in-the-periphery-of-the-human-retina-connect-to-multiple-types-of-cone-cells-red-green-blue-Thus-does-peripheral-vision-have-more-muted-colors-than-central-vision-where-1-cone-connects-to-1-retinal-ganglion-cell A.K.Khurana. Indu Khurana “Anatomy and physiology of eye”; Modern system of ophthalmology (MSO) series; CBS Publishers and distributors.

17. https://openbooks.lib.msu.edu/introneuroscience1/chapter/vision-the-retina/

18. STRUCTURE OF PHOTORECEPTORS:- RODS 40-60 μ m long Outer segment :- Cylindrical, highly refractile, transversely striated Contains visual purple. Composed of numerous lipid protein lamellar disc stacked one on top of the other and surrounded by cell membrane. The number of disc - 600 and 1000/rod E ach disc is 22.5-24.5 nm in thickness Disc contains 90% visual pigment is scattered on the surface of the plasmalemma A modified cilium (or basal body) connects the outer segment to inner segment Inner segment:- Thicker than the outer segment. It consist of two regions:- Ellipsoid and M yoid . Ellipsoid – adjacent to outer segment; abundant number of mitochondria. Myoid - Contains glycogen. https://physics.aps.org/articles/v5/103

19. STRUCTURE OF PHOTORECEPTORS:- RODS Outer rod fiber:- Mathur , Pranav & Yang, Jun. (2014). Usher syndrome: Hearing loss, retinal degeneration and associated abnormalities. Biochimica et biophysica acta . 1852. 10.1016/j.bbadis.2014.11.020.

20. https://sciencesource.com/1085586-sem-of-rods-and-cones-of-the-retina-stock-image-rights-managed.html

21. STRUCTURE OF PHOTORECEPTORS:- CONES 40-80µm long. Largest at fovea (80µm) and shortest at the periphery(40µm). Outer segment:- Conical and shorter than rods Contains iodopsin The lamellar discs narrower than rods . Maintains continuity of the surface plasma membrane. 1000-1200 discs/cone Inner Segment:- Cilium are similar to rod structure Cone ellipsoid : very plump and contains large number of mitochondria. Continuous with its nucleus and lies outer nuclear layer. Cone foot :- Stout cone inner fiber runs from the nucleus and form lateral branches.

22. https://www.differencebetween.com/difference-between-rod-and-vs-cone-cells/

23. INTERPHOTORECEPTOR MATRIX (IPM) AND INTERPHOTORECEPTOR RETINOID BINDING PROTEIN(IRBP ) IPM:- Occupies the space between photoreceptor outer segment and retinal pigment epithelium. Consists of proteins, glycoproteins ,GAGS and proteoglycans( chondroitin sulphate ). Function :- Retinal attachment, adhesion molecular trafficking, facilitation of phagocytosis and photoreceptor outer segment alignment. IRBP :- Constitutes 70% of soluble protein of IPM. Produced by photoreceptors. Can bind with all-trans-retinal, 14-cis-retinal, α - tocopherol , retinoic acid and cholesterol. Function :- (a) Efficient transport of retinoid between photoreceptors and the RPE (b) minimize fluctuation between retinoid availability (c) Protects plasma membrane from damaging effects of high retinoid concentration. Cellular retinoid binding protein (CRBP):- Subgroup of fatty acid binding protein that orchestrate reisomerization in the RPE Has a vital role in early retinal development.

24. 10 YEARS QUESTION PAPER Q)Short answer type question:- (1 mark each) a)The outer blood-retinal barrier is formed by_ b)Blue sensitive cone pigment is known as- c)Color vision is due to – d) The area of retina where there is absence of rods and cone cells is called- Q. Write short note on Blood retinal barrier.(5) Q. Draw and describe the parts and function of typical rod and cone cells of a retina .(10)