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- 1. RETINA monika pallan & afasanapathan ANATOMY & PHYSIOLOGY
- 2. Retina • Retina isthe innermost tunic of the eyeball • Thin,delicate,transparent membrane • Highly developed tissue of the eye • Appears purplish red
- 3. Grosss anatomy • Threedistinct regions of retina: • 1.optic disc • 2.macula lutea • 3.peripheral retina • retina extends from optic disc to ora serrata • Surface area:266sq/mm
- 4. Optic disc • Palepink in colour; well defined circular area • Diameter: 1.5mm • All the retina layers terminate here,except the nerve fibre which pass through the lamina cribrosa
- 5. Macula lutea • Themacula lutea is comparatively dark area 5.5 mm in diameter , situated at the posterior pole of the eyeball , temporal to optic disc • also called as yellow spot or area centralis • Primary function :- photoptic vision • Fovea centralis is central depression in macula;measurin 1.85 mmin diameter & 0.25 thickness • It is most sensitive part of retina
- 6. Foveola • Diameter:- 0.35 •Central floor of fovea • Umbo is the tiny depression in centre of foveola macula Fovea centralis foveola umbo
- 7. Peripheral retina • Theperipheral retina can be divided into four regions 1. Near periphery 2. mid periphery 3. Far periphery 4. Ora serrata
- 8. Microscopic structure ofthe retina 1. Retinal pigment epithelium 2. Layer of rods and cones 3. External limiting membrane 4. Outer nuclear layer 5. Outer molecular (plexiform) layer 6. Inner nuclear layer 7. Inner molecular (plexiform) layer 8. Ganglion cell layer 9. Nerve fibre layer 10. Internal limiting membrane
- 9. Retinal pigment epithelium(RPE) • It is the outermost layer of retina • Made up of single layer of hexagonal cells • The cells contain pigments • It is firmly adherent to the underlying brush layer & loosely attached layer of rod and cone cells • Sub-retinal space :- potential space betn RPE & retina
- 10. Conts…… • Retinal detachment:- separation of RPE from retina Sub- retinal fluid :- fluid betn sensory retina & RPE . RPE cells are connected to each other by zonule occludents & zonule adherence
- 11. Functions of RPE •Renewal of photoreceptor & recycling of Vit A • Provides mechanical support to process of photoreceptors • Manufacturing of pigments absorbing light • RPE cells are phagocytic
- 12. Layer of Rods& Cone cells • Rods & cones transform light energy into nerve impulses • Rods contain photosensitive substance rhodopsin whereas cones contain photosensitive substance idopsin • Cone cells - photoptic vision • rod cells - scotoptic vision Cones :- 6.5 million Rods :- 120 million
- 14. Conts…… • At fovea:-max cones(199000cones/mm.sq) & rods are absent • Density:- 100000- 324000 cones/mm.sq • 160000 rods/mm.sq
- 15. Structure of rodcell • Length :- 40-60 um • Outer segment is cylindrical composed of numerous protein lamellar disc • Dics :- 600- 1000/rod • Thickness of disc :- 22.5 -24.5 nm • Disc contains 90% of visual purple • Outer segment is attached to inner segment via cilium • Inner segment :- consist of ellipsoid & myoid region •
- 16. Conts….. • Outer rodfibre arises from inner end of rod & passes through external limiting memebrane further swells into densely stained nucleus • The nucleus terminates further into inner rod fibre • The inner rod fibre ends as a bulb called rod spherule
- 17. Cone cells • Length:- 40-80um • At periphery :- 40um ( shortest) • At fovea :- 80um (longest) • Outer segment is conical :shorter than rod • Contains idopsin pigment packed in lamellar disc • Disc :- 1000-1200 disc/cone • Inner segment & cilium are similar to rods • Inner segment is directly continous with nucleus • A stout cone inner fibre runs from the nucleus & has lateral processes at the end called cone foot / cone pedicel
- 18. External limiting membrane •Fenestrated membrane extending from the ora serrata upto the edge of optic disc • Processes of rods & cones pass through it • This layer is formed by the junction betn the cell membrane of photoreceptors & mullers cell
- 19. Outer nuclear layer •Made up of the nuclei of rods & cones • Cone nuclei:- 6-7 um • Rod nuclei :-5.5um • These nuclei lie in a single layer next to external limiting membrane • Rod nuclei form the bulk of this layer except at cone dominated foveal region
- 20. Variation in Thickness •Nasal to disc:- 45um ( 8-9 layers ) • Temporal to disc :- 22um (4 rows) • Foveal region :- 50um (10 rows) • Rest of retina except ora serrata – 27 um (1 row of cones & 4 rows of rods)
- 21. Outer plexiform layer Thislayer is made of synapses betn the rod spherules & cone pedicles with the dendrites of bipolar cells
- 22. Inner nuclear layer •It is very thin & is similar to outer nuclear layer • It consists :- Bipolar cells Horizontal cells Amacrine cells Mullers cells Central retinal vessels Other glial cells This layer disappers at fovea
- 23. Inner plexiform layer •Consists of synapse betn bipolar cell & dendrites of ganglion cell • Absent at fovea
- 24. Ganglion cell layer •Consist of cell body & nuclei of ganglion cell ( 2nd order neurons) • Absent at fovea • Various types of ganglion cell:- 1) W,X,Y ganglion cell 2) P(P1 &P2) & M GANGLION CELL 3) Off centre & on centre cell 4) Monosynaptic & polysynaptic cell
- 26. Nerve fibre layer •Consists of unmyelinated axons of ganglion cells which converge at optic nerve head • Thickness:- 0.5-2 um • Thickness decreases from optic disc to lateral side • Fibres show definite pattern of arrangement
- 27. Internal limiting membrane •Consists of following elements:- • 1) collagen fibrils • 2) proteoglycans of vitreous • 3) basement membrane • 4) plasma membrane of muller cells • 5) other glial cells
- 28. Blood supply ofretina • Outer 4 layers :- choriocapillaries • Inner 6 layer:- central retinal artery • Fovea :- choriocapillaries • Macular region:- superior & inferior temporal branches of central retinal artery
- 29.
- 30. PHYSIOLOGY OF VISION •It is a complex phenomenon • Main mechanism concerned with vision :- • 1)Transduction • 2) Transmission of visual sensation • 3) Visual perceptions
- 31. transduction • Rods &cones serve as a sensory nerve ending for visual senasation • Stimulus inadequate adequate
- 32. Inadequate stimulus • 4types of stimulus:- • Pressure phosphane • Movement phosphane • Electrical phosphane • Radiation phosphane
- 33. Adequate stimulus • Visibleportion of EM spectrum forms the adequate stimulus • Visible portion of light lies betn uv rays & infrared rays • Visible portion :-400 nm -750nm • The visible consists of VIBGYOR ( 7 colours)
- 34. Transmission of visualsensetion Photochemical changes take place Light absorbed by rods and cones pigment Electrical impluses are arise Information is forwarded thuru ganglion cells Optic nerve Optic chiasma Optic tract LGB Optic radiation Visual cortex
- 35. Visual perceptions • Functionalelements of vision • 1)light sense:- appreciation of light • 2)Form sense :- most acute at fovea • 3)Constrast sense :- differentiate bet luminance which are not separated by definite borders • 4) Colour sense :- discriminate betn colours
- 36. Photochemistry of vision •Light falling on the retina is absorbed by rods & cones , further photochemical changs takes place • It includes:- • Vit A • Visual pigments • Light induced changes
- 37. Vitamin A (food) Dietarysource of vit A (Intestine) Digestion,absorption& transport (Liver) 1.Storage of vit A 2.Production of retinol in liver cells as binding protein retinol (Blood) Transport of retinol bound to retinol- binding protein (eye) 1.formation of 2.maintainance of healthy rhodopsin corneal & conjunctival cells
- 38. Visual pigments • Thesepigments absorbs light • The peak of each pigment ‘s absorption is called its absorption maximum Peak absorption Wavelength (nm) % of aborption
- 39. Rhodopsin pigment • Alsoknown as visual purple • Present in the outer segment of rods • photopsin + retinol Rhodopsin • Rhodopsin protein is insoluble in water ; sensitive to strong acids & alkalis • Peak sensitivity : 493- 505nm • Absorbs yellow wavelength of light;transmitts violet to red colour ,hence appears visual purple
- 40. Cone pigments • 3kinds of cone pigments • These are different from rhodopsin pigments • Responsible for colour vision • Cone pigments are different from rhodopsin in opsin portion;11 cis retinol is same as rhodopsin • Peak absorbance:- • Blue sensitive cones:- 435 nm • Green sensitive cones:- 535 nm • Red sensitive cones:-580 nm
- 41. Light –induced changes •Rhodopsin bleaching • Rhodpsin regeneration • Visual cycle • Photochemistry of photoptic vision
- 42. rhodopsin bleaching& regeneration •Rhodopsin Barthorhodopsin Lumirhodopsin Metarhodopsin | Metarhodopsin || All trans-retinal All trans -retinol isomerase 11 cis -retinol 11 cis-retinal opsin NADH NAD NADH NAD
- 43. Visual cycle • Rateof photodecomposition = rate of photoregeneration rhodopsin All trans retinal 11 cis -retinal opsin Light energy opsin
- 44. Photochemistry of photopicvision • Like rhodopsin ,cone pigments also consists of protein opsin i.e photopsin & retinine • Photopsin differs slightly from rhodopsin • 3 classes of photopsin :- • Erythrolabe – red sensitive • Chlorolabe – green sensitive • Cyanolabe- blue sensitive
- 45.