ANATOMY OF RETINA !.pptx with detailed description

Brief description with proctorial introduction
Detained one by cell description

1. ANATOMY OF RETINA

2. INTRODUCTION Thin , delicate and transparent membrane forming innermost coat of eye Most highly developed tissue of eye Color - purplish red due to visual purple of rods

3. Extends from optic disc to ora serrata Surface area 266 mm 2 Thickness - Thickest at peripapillary region ( 0.56mm) Equator (0.18 - 0.20 mm) Ora serrata (0.1mm)

4. DEVELOPMENT OF RETINA -Outer wall of optic cup forms RPE -Inner wall of optic cup forms neural retina -all layers identifiable by 5.5 months except macula which is delayed thill 8th month. Specialisation of macula continues for several months after birth

5. Regions of retina Fundus can be divided into 3 regions Optic disc Macula lutea Peripheral retina

6. OPTIC DISC Circular , well defined area of 1.5 mm diameter Pale pink due to medullated nerve fibre behind it and absence of vascular choroid All layers terminate here except NFL which runs into optic nerve Grey spots in lamina = medullated nerve fibres Physiological cup - central depression

7. MACULA LUTEA / AREA CENTRALIS Elliptical 5.5mm diameter with dark area (yellow spot ) situated at posterior pole , 4mm temporal and 0.8 mm inferior to optic disc It consists of more than one layer of ganglion cell It corresponds to 15 degree of visual field Function - photopic and color vision Yellow due to presence of oxygenated carotenoids ( lutein and zeaxanthine ) which act as antioxidant and filter blue light therefore preventing photopic damage

8. Areas of macula

9. FOVEA Concave depression in inner retinal surface Photoreceptor - only cones 1.5 mm diameter ( 5 degree visual field) 1.55mm thick Most sensitive part of retina Consists of a margin , clivus ( declinity of 22 degree) and foveola (floor) CLIVUS = 22 degree declinity from margin of fovea to foveola Consists of peripheral vascular area and central avascular zone . clivus

10. FOVEOLA Central floor of fovea 0.35mm diameter and 0.15 mm thick Inner nuclear layer and ganglion cell layer absent Correspond to 1 degree of visual field Corresponds to foveal avascular zone UMBO- small central concavity in floor of foveola Corresponds to normal light reflex Consists central bouquet of cones(highest concentration of cones) 150 to 200 µm diameter

11. PARAFOVEAL ZONE 0.5mm ring surrounding Outermost limit of fovea Consists 4-6 Ganglion cell layer and 7-11 bipolar cell layer PERIFOVEAL ZONE Extends from outermost limit of parafoveal to outermost limit of macula 1.5mm ring around parafovea Several layers of ganglion cell layer and 6 layers of bipolar cell layer

12. PERIPHERAL RETINA 4 REGIONS Near periphery - 1.5mm around macula Mid periphery - 3mm around near periphery Outer limit-equator Far periphery - equator to ora serrata 6mm width Extreme periphery - ora serrata to pars plana Ora serrata - termination of retina

13. ORA SERRATA Serrated peripheral margin of retina 2.1mm wide temporally while 0.7-0.8 mm nasally Located 6-8mm from equator, 6 and 7 mm respectively from nasal and temporal limbus ,25mm from optic nerve nasally It is the watershed zone between anterior and posterior vascular system

14. MICROSCOPIC STRUCTURE OF RETINA -10 LAYERS

15. RETINAL PIGMENT EPITHELIUM Outermost layer Single layer of hexagonal cells containing pigments Cells show fine mottling due to unequal pigmentation Firmly adherent to bruch’s membrane but loosely attached to layer of rods and cones Potential space between RPE and sensory retina = subretinal space Forms outer blood retinal barrier Foveal RPE cells are taller , Thinner and have larger pigment granules therefore appears dark

16. Apical part consists of microvilli projecting into layer of rods and cones Melanin is concentrated apically in cytoplasmic granules called melanosomes. Melanin absorbs stray light and minimises scatter It also consists of lipofuscin pigments which accumulates with age Basal membrane - increase surface area for absorption and secretion

17. FUNCTIONS OF RPE Photoreceptor renewal and recycling of vitamin A forms outer blood-retinal barrier transport of nutrients and metabolites Phagocytic action and digestion of photoreceptors. mechanical support to photoreceptors Manufactures pigment which presumably has an optical function in absorbing light. Regenerative and repairative function after injury and surgery. Electrical homeostasis

18. b. Neurosensory retina 3 types of cells and their synapses in 9 layers LAYER OF RODS AND CONES ( NEUROEPITHELIUM) Only consists of outer segments of photoreceptors arranged in palisade manner They are end organs of vision

19. RODS CONES 120 million 6.5 million Rhodopsin pigment Iodopsin pigment Peripheral and scotopic vision Low visual acuity Discriminatory central vision (photopic) and color vision High visual acuity Absent at fovea - 0.35mm rod free zone , 1.25 degree of visual field Abundant 5-6 mm from fovea ( 160000 /sq mm) Maximum - below optic disc (170000/ sq mm) Highest density at fovea (199000/sqmm) 6000/sq mm 3mm away from fovea 4000/sq mm 10mm away from fovea Density 20-25% more nasally than temporally Density 2% more superiorly than inferior Density 40-45% greater nasally than temporally Densite lower superiorly than inferiorly at mid periphery Inner end has a small knob Inner end is branches Outer segment cylindrical, stacked lamellar discs Outer segment conical, discs continuous with plasma membrane Ends in rod spherule Ends in cone pedicles Several rods synapse with one bipolar cell One cone with one bipolar cell

20. STRUCTURE OF PHOTORECEPTOR The long axis of the photoreceptor is oriented perpendicular to the retinal surface. Each photoreceptor consists of: • Cell body and nucleus -lie in the outer nuclear layer,cell process - extends into outer plexiform layer and • Inner and outer segments - form the layer of rods and cones

21. ROD CELL 40-60 micrometre Outer segment : cylindrical, refractile Transversely Striated contain rhodopsin Lipid protein lamellar discs stacked on each other 600-1000/ rod each 22.5 -24.5 nm 90% visual pigment on plasmalemma Cilium : connects outer and inner segment

22. Inner segment : Thicker Ellipsoid : outer , mitochondria Myoid : inner , glycogen Outer rod fibre : passes ELM and forms rod granule containing nucleus Terminate in inner rod fibres which ends in rod spherule - in contact with cone pedicle

23. CONE CELL •40- 80 micrometer long •Largest at fovea shortest at periphery •Outer segment conical contains iodopsin 1000-1200 lamellar disc per cone, continuous with plasma membrane Inner segment - continuous with its nucleus

24. 2. External limiting membrane •Fenestrated membrane that extents from ora serrata to edge of optic disc •Formed by junctions between the cell membrane of photoreceptors and mullers cell •the process of cones and rods passes through it Not a true basement membrane

25. 3. Outer nuclear layer Formed by the nuclei of rods and cones •cone nuclei are larger (6-7 µm) than rod nuclei (5.5 μm) and lie in a single layer next to the external limiting membrane. •Rod nuclei form the bulk of this multilayered outer nuclear layer except in the cone dominated foveal region. Nasal to disc Temporal to disc fovea Rest of retina Except ora serrata 8-9 rows 45 micron 4 rows 22 micron 10 rows 50 micron 1 row cone and 4 rows rod 27 micron

26. 4. Outer plexiform layer Synapses between the rods spherules and cone pedicles with the dendrites of the bipolar cells and processes of the horizontal cell Thickest at the macula (51 µm) and consists predominantly of oblique fibres; also known as Henle’s layer.

27. 5. Inner nuclear layer Thin Absent at fovea Made of- • Bipolar cells Horizontal cells Amacrine cells The soma of the Muller’s cells Capillaries of the central retinal vessels

28. Bipolar cells 1st order neuron •The body of the bipolar cells consists entirely of nucleus -lies in the inner nuclear layer. •Their dendrites arborize with the rod spherules and cone pedicels in the outer plexiform layer •Axons arborize with the dendrites of ganglion cells - inner molecular layer.

29. Types - 9 types 1 .Rod bipolar cells (20%) 2. Invaginating midget bipolar cells 3. Flat midget bipolar cells 4. Invaginating diffuse bipolar cells 5. Flat diffuse bipolar cells 6. On-centre blue cone bipolar cells 7. Off-centre blue cone bipolar cells 8. Giant bistratified bipolar cells 9.Giant diffuse invaginating bipolar cells.

30. Horizontal cells Flat cells horizontal associative and neuronal interconnections between photoreceptors and bipolar cells in the outer plexiform layer. Type A horizontal cells -have seven groups of dendrites which have contact with triad of seven cone pedicles and their single axon has contact with distant cone triad. Type B horizontal cells- dendrites have contact with rod receptors only and axons with the distant rod cells.

31. Amacrine cell situated within the innermost part of this layer. •These have a piriform body and a single process which passes inwards in the inner plexiform layer and • forms connections with the axons of the bipolar cells and the dendrites and soma of the ganglion cells • function similar to that of the horizontal cells

32. Mullers cell •The nucleus and cell bodies of the Muller’s cells are located - inner nuclear layer •Fibres from their outer ends extend up to the external limiting membrane and those from their inner ends reach up to the internal limiting membrane. •Provide structural support and contribute to metabolism of the sensory retina.

33. 6. Inner plexiform layer •This layer essentially consists of synapses between the axons of bipolar cells (first order neurons), dendrites of ganglion cells (second order neurons) and the processes of integrative Amacrine cells •This layer is absent at the foveola

34. 7. Ganglion cell layer second order neurons •Throughout retina single layer of cells, except in the macular region : 6-8 layers of the cells and on temporal side of the disc - 2 layers. •Ganglion cell layer is absent in the region of foveola. •Ganglion cells classified as follows: W, X and Y ganglion cells P(P1 and P2) and M ganglion cells OFF-centre and ON-centre ganglion cells. Monosynaptic and polysynaptic ganglion cells

35. 8. Nerve fibre layer/ stratum opticum unmyelinated axons of the ganglion cells, converge at the optic nerve head Processes of Mullers cells Neuroglial cells - macroglia -structural role Microglia -the role of wandering tissue histiocytes in response to tissue injury and phagocytosis Retinal vessels

36. Arrangement nerve fibres in the retina Nasal half - srf and irf ( superior and inferior radiating fibres) Temporal half except macula - saf and iaf ( superior and inferior arcuate fibres) separated by horizontal raphe Macula - pmb ( papillomacular bundle )

37. Arrangement of nerve fibres in optic disc

38. Thickness of nerve fibre layer at the disc Increasing order • Most lateral quadrant (thinnest) • Upper temporal and lower temporal quadrant •Most medial quadrant Upper nasal and lower nasal quadrant (thickest)

39. Clinical significance •Papilloedema - first in the thickest quadrant (upper and lower nasal) and last of all in the thinnest quadrant (most lateral). Arcuate nerve fibres which occupy the superior temporal and inferior temporal quadrants of optic nerve head = most sensitive to glaucomatous damage, Macular fibres occupying the lateral quadrant = most resistant to glaucomatous damage

40. 9. Internal limiting membrane PAS positive true basement membrane; forms interface between retina and vitreous Consists of Collagen fibrils Proteoglycans (mostly hyaluronic acid) of the vitreous Basement membrane Plasma membrane of Muller cells and glial cells of retina.

41. Structures at fovea centralis no rods cones are larger, in abundance and tightly packed, and other layers are very thin foveola- largely consists of cones and their nuclei covered by a thin internal limiting membrane. All other layers are absent Cone axons are arranged obliquely (henles layer) to reach margin of fovea

42. Blood supply of retina Outer 4 layers Inner 6 layers macula Fovea is avascular

43. Central retinal artery first branch of ophthalmic artery, arises near the optic foramen

44. Blood supply retina

45. In optic nerve head Here, it divides into two branches-a superior and an inferior, each of which subdivides into a temporal and a nasal branch at or near the margin of the optic disc.

46. Arrangement of retinal capillaries In most of the extramacular funds , there are two retinal capillary networks- Superficial - nerve fibre layer Deep - between the inner nuclear layer and the outer plexiform layer more dense and complex Peripherally, the capillary network is reduced to a scanty single layer PARAFOVEAL ZONE 3 layered PERIPAPPILARY REGION 4 layered

47. Blood retinal barrier Endothelial cells of retinal capillaries basement membrane a layer of pericytes (mural cells). layer of basement membrane Endothelium: pericyte 1:1 Diabetes and increase in age - relative decrease in number of pericyte

48. Thank you