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Anatomy of the Retina.pptx

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This document provides an overview of the anatomy of the retina through a presentation given by an ophthalmology resident. It describes the gross anatomy of the retina including key structures like the macula and fovea. It also discusses the embryological development of the retina from the optic cup and explains the microscopic anatomy including the layers of the retina and cellular structure of the retinal pigment epithelium. Finally, it briefly touches on the blood supply of the retina.

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12/07/2010EC. MuezA 1 Anatomy of the Retina Presenter; Muez A. (1st year Ophthalmology Resident) Moderator; Dr Demoze (Consultant vitreoretinal Surgeon)
Out line Introduction Gross anatomy Embryology Microscopic anatomy Blood supply 12/07/2010EC. MuezA 2
Introduction Inner posterior 2/3rd of the eye ball Continuous posteriorly as optic nerve, anteriorly with the ciliary body Bordered by the vitreous internally & the Bruchs membrane externally It has pigment epithelium and neural layer Surface area of about 266 mm2 Thickest in the papillomacular bundle near the optic nerve (0.23 mm) thinnest in the foveola (0.10 mm) and ora serrata (0.11 mm). Site of transformation of light energy into a neural signal. 12/07/2010EC. MuezA 3
Gross anatomy The major landmarks of the retina The area centralis The peripheral retina The optic disc The retinal blood vessels 12/07/2010EC. MuezA 4
Central Retina Rich in cones, has more ganglion cells per area than elsewhere Small portion of the entire retina. 1. Foveola 2. Fovea 3. Para fovea 4. Perifovea 5. Macula Clinical function Fine visual acuity Photopic vision Stereopsis Color vision 12/07/2010EC. MuezA 5
Macula Demarcated by superior and inferior temporal arterial arcuate Dark area in the central retina Elliptical shape horizontally Average diameter of about 5.5 mm/3.5DD 15-18属 of visual field Protects central vision by following characteristics; Highly pigmented tall epithelial cells of RPE(highest pigmentation ) reduce scattering of light The choroidal capillary bed also is thickest in the macula Highest concentration of xanthophyll pigments Act as filters, absorbs short wavelength visible light to reduce chromatic aberration Antioxidant effect Protective role against UVR damage. 12/07/2010EC. MuezA 6
12/07/2010EC. MuezA 7
FOVEA center of macula Diameter of 1.5-1.85mm/1DD Represents 5属 of the visual field Central depression foveola The inner nuclear layer and ganglion cell layer are displaced laterally and accumulate on the curved walls of the fovea called Clivus The fovea has the highest concentration of cones (199,000-300,000 cones/mm) The photoreceptor fibers(cones) become longer as they deviate away from the center; these fibers are called Henles fibers 12/07/2010EC. MuezA 8
Foveola Central depression in the fovea 1属 of visual field 0.35mm in D/0.3-0.4DD Six layers present in the foveola Internal limiting membrane Henles fiber layers ONL External limiting membrane Photoreceptor layers RPE form sharpest vision and steoropsis Umbo (Center of foveola) corresponds to light reflex Foveal reflex is due to the parabolic shape formed by the clivus. Loss of foveal reflux implies disruption of neural layers 12/07/2010EC. MuezA 9
Clinical correlates; Lack of blood vessels and neural tissue in foveola allows light to pass unobstructed into the photoreceptor outer segment Chronic retinal oedema may result in the deposition of hard exudates around the fovea in the layer of Henle with a macular star configuration 12/07/2010EC. MuezA 10
12/07/2010EC. MuezA 11
Rods reduces and are replaced by malformed cones The nuclear layers merge with the plexiform layers, Finally, neural retina becomes a single layer of irregular columnar cells that continue as the nonpigmented epithelium of the ciliary body. TheRPE is continuous with the outer pigmented epithelium of the ciliary body, the internal limiting membrane continues as the internal limiting membrane of the ciliary body. 12/07/2010EC. MuezA 12
Ora Serrata The ora serrata is the boundary between the retina and the pars plana. A firm attachment between the retina and vitreous Its distance from the Schwalbe line is between 5.75 mm nasally and 6.50 mm temporally. In myopia, this distance is greater; in hyperopia, it is shorter. The Bruch membrane extends anteriorly, beyond the ora serrata, but is modified because there is no choriocapillaris in the ciliary body 12/07/2010EC. MuezA 13
Topographically, the ora serrata is relatively smooth temporally and serrated nasally. Retinal blood vessels end in loops before reaching the ora serrata. The ora serrata is in a watershed zone between the anterior and posterior vascular systems peripheral retinal degeneration is relatively common. The photoreceptors are malformed, and the overlying retina frequently appears cystic (Blessing Iwanoff cysts) 12/07/2010EC. MuezA 14
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PERIPHERAL RETINAL DEGENERATION Cystic spaces and atrophied areas often are found in peripheral retina and their incidence increases with age. poor blood supply in the extreme retinal periphery. others might predispose the affected dilated fundus examinations. 12/07/2010EC. MuezA 17
12/07/2010EC. MuezA 18
cont. The number of nerve fibers appears to be positively correlated with the size of the optic nerve head larger discs have relatively more fibers than smaller discs Smaller discs may demonstrate optic nerve head crowding. Fiber number decreases with age. The pale-yellow or salmon color of the optic disc is a combination of the scleral lamina cribrosa and the capillary network. 12/07/2010EC. MuezA 19
12/07/2010EC. MuezA 20
Optic DISC ASSESSMENT The color of the disc configuration and depth of the physiologic cup cup-to-disc ratio appearance of the rim tissue disc borders are assessed during an ocular health examination. 12/07/2010EC. MuezA 21
Embryology 12/07/2010EC. MuezA 22
12/07/2010EC. MuezA 23
Retinal pigment epithelium The first retinal layer to be formed (3-4 month) the earliest pigmentation evident in the embryo one cell thick, the cells are cuboidal to columnar in shape the base of each cell is external toward the developing choroid the apex internal toward the inner layer of the optic cup 12/07/2010EC. MuezA 24
The neural retina week 7, cell migration occurs, forming the inner and outer neuroblastic layers Outer neuroblastic layer differentiates to photo receptor cells,bipollar cells and horizontal cells (outer plexiform) Inner neuroblastic layer differentiates to Ganglion cell, amacrine, and M端ller cells (inner plexiform layer) The photoreceptor cells are the last cells of neural retina to differentiate (5th month) Differentiation of the neural retinal cells begins in central retina and proceeds to the periphery The Muller cells forms the internal limiting membrane 12/07/2010EC. MuezA 25
6 months dense accumulation of nuclei in the macular area makes this region thicker than the rest of the retina the ganglion axons from the periphery take an arched route above and below the macular area to reach the nerve head. Foveal development consists of three stages (1) displacement of inner retinal components to form the depression; (2) migration of photoreceptors toward the center, which increases cone packing (3) maturation of the photoreceptors. At 7month the ganglion and inner nuclear layer cells begin to move to the periphery of the macula. By 4 months postpartum, both these layers are displaced 12/07/2010EC. MuezA 26
The foveal depression continues to deepen until about age 15 months The foveola, the retinal area of sharpest visual acuity, is the last to reach maturity. migration of the cones centrally, increasing cone density. The cone inner fibers elongate and adopt an oblique orientation (forming Henles fiber layer) in order to synapse with the cells of the inner nuclear layer, which have been displaced to the sloping walls 12/07/2010EC. MuezA 27
CLINICAL COMMENT: COLOBOMA Incomplete closure of the optic fissure may affect The developing optic cup or stalk and the adult derivations of these structures, resulting in an inferior nasal defect in the optic disc, retina, ciliary body, or iris. 12/07/2010EC. MuezA 28
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1.Retinal pigment Epithelium 4-8 million cells firmly attached to its basal lamina Single cell thick and consists of pigmented hexagonal cells Columnar in the area of the posterior pole densely pigmented in the macular area. Larger and more cuboidal less pigmented as the layer nears the ora serrata, Phagocytic cells 12/07/2010EC. MuezA 31
Contain numerous melanosomes,pigment granules Pigment density differs in various parts of the retina Densest at the macula and at the equator decreased transmission of choroidal fluorescence observed during fundus fluorescein angiography Lipofuscin granules arise from the discs of photoreceptor outer segments and represent residual bodies arising from phagosomal activity This so-called wear-and-tear pigment less electron dense than the melanosomes increases gradually with age. 12/07/2010EC. MuezA 32
Other material are excreted beneath the basal lamina of the RPE formation of drusen( accumulations of this extracellular material) can vary in size and are commonly classified by their funduscopic appearance as either hard or soft. located between the basement membrane of the RPE cells and the inner collagenous zone of the Bruch membrane. 12/07/2010EC. MuezA 33
RPE - Cell Surfaces characteristics Clinical significances; No specialized junctional complex between RPE and photoreceptors- loosely adhered Potential space exists (subretinal space)- prone for RD) 34 Apical surface Has microvillous processes- Increases Surface area Interdigitate with outer segments of photoreceptor cells Contains melanin granules more dense in macular region 1.Apical surface inner surface 2.Paracellular (lateral) surface-intercellular surfaces 3.Basal surface outer surface
Paracellular surface; Contains tight junction( Zonula Occluden & adheran, gap junctions) Junctional complex form blood-retinal barrier Maintains retinal homeostasis and prevents from toxic damages 35 Basal surface; Attached to its basal lamina, the lamina vitrea of Bruch's membrane. Nutrients from choriocapillaries difusess to RPE through basal lamina
Sensory neural retina Transparent layer Contains 3 basic cell types photoreceptor cells Rods and cons120 million vs 6 million respectively Constitutes the outer nuclear layer and the outer plexiform layer. Neuronal cells Bipolar cells Horizontal cells 1st order neurons Amacrine cells Ganglion cells 2nd order neurons Glial cells Muller cells Astrocytes Microglial cells 12/07/2010EC. MuezA 36
M端ller cells are large neuroglial cells that extend much of the retina. Supportive role, and providing structure Fill in most of the space of the retina not occupied by neuronal elements Ensheathe dendritic processes within the synaptic layers, providing insulation from electrical and chemical activation, Involved in glucose metabolism by synthesizing and storing glycogen Buffer in regulating concentrations of potassium ions (K+),GABA, and glutamate in the extracellular space. Apex in the photoreceptor layer, basal aspect is at the inner retinal surface Apical villi, fiber baskets (of Schultze), terminate between the inner segments of the photoreceptors. 12/07/2010EC. MuezA 37
12/07/2010EC. MuezA 38
Microglial cells are wandering phagocytic cells found anywhere in the retina. increases in response to tissue inflammation and injury. Astrocytes star-shaped fibrous cells found in inner retina, usually in the nerve fiber and ganglion cell layers. perivascular cells form an irregular supportive network encircles nerve fibers and retinal capillaries. contribute to the internal limiting membrane Amacrine cells No axons. Stimulated by the Bipolar cells & then they excite the Ganglion cells 12/07/2010EC. MuezA 39
Bipolar cells First order neuron in the visual pathway. Its dendrite synapses with photoreceptor and horizontal cells Axon synapses with ganglion and amacrine cells Eleven types of bipolar cells have been classified on the basis of morphology, physiology, and dendritic contacts with photoreceptors Horizontal Cells They have one long & several short processes. Inhibitory function by releasing GABA. highest concentration in fovea Modulate and transform visual information received from the photoreceptors Have a role in sharpening contrast 12/07/2010EC. MuezA 40
Ganglion cells 2nd order neurons W cells project to the midbrain, carrying information for the pupillary response and reflexive eye movements. Y cells project to the lateral geniculate body, with some having collateral branches that travel to the midbrain, perhaps with pupillary information X cells primarily respond in visual discrimination and project to the lateral geniculate body P ganglion cells ; color vision stereopsis M ganglion cells ; rapidly to moving or changing stimuli. 12/07/2010EC. MuezA 41
2. Photoreceptors CONES 4_8 million cells density is maximum at fovea (199 000 cones/mm2) -minimum density- periphery light sensitive molecule Iodopsin ( color vision- photopic vision) ( 3 types of iodopsin trichromatic pigments 1. S wavelength cones- 440nm blue light) 2.M wavelenght cone- 540nm green 3. L wavelenght cone- 577nm red RODES 100-130 million cells maximum density in 20属(3mm) from the fovea(160,000 rods/mm2) rod-free at the fovea ; 0.35 mm minimum density periphery light sensitive molecule- rhodopsin ( night vision- scotopic vision) rhodopsin is sensitive to blue-green light- 493nm Main for white and black Clinical notes Mutation of rhodopsin in retinitis pigmentosa With advanced of age there is progressive loss of photoreceptors (rods are affected more than cone) poor night vision in elderly 12/07/2010EC. MuezA 42
Morphology of Photoreceptors Rods and cones have six main parts 1. The outer segment, containing the visual pigment molecules for the conversion of light into a neural signal 2. A connecting stalk, the cilium(cytoplasmic isthmus) 3. The inner segment, containing the metabolic apparatus; 4. The outer fiber; 5. The cell body- forms outer nucleated layers 6. The inner fiber, which ends in a synaptic terminal outer plexiform layer 12/07/2010EC. MuezA 43
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the outer segments of the rods and cones difference. Rod discs are not attached to the cell membrane Cone discs are attached to the cell membrane renewed by membranous replacement. cone synaptic body, or pedicle, is more complex than the rod spherule. Cone pedicles synapse with other rods and cones as well as with horizontal and bipolar cell processes. Foveal cones have cylindrical inner segments similar to rods but otherwise are cytologically identical to extrafoveal cones. 12/07/2010EC. MuezA 45
The Rods The most light sensitive cells Components of disc membranes are produced in the inner segment Discs contain 90% of the visual pigment remaining is scattered on plasma membrane. move along the connecting stalk to be discs at the outer segment The discs gradually displaced outward and form new discs and sloughed off and phagocytosed the rod outer segment renewal system shed regularly, with mostly occurring in the early morning. The inner fiber extends from the cell body and terminates in structure called a spherule The spherule forming a synaptic complex with bipolar dendrites and horizontal cell Rods release the neurotransmitter glutamate 12/07/2010EC. MuezA 46
Cones The cone outer segment is shorter Dont not reach the RPE layer. Tubular processes protrude from the apical surface of the epithelial cell to surround the cone outer segment Cone at periphery is short but in central fovea it is tall and resembles rod As with rods, cones use glutamate for aneurotransmitter. 12/07/2010EC. MuezA 47
The photoreceptor cell layer and the RPE layer. Passive forces intraocular pressure (IOP) osmotic pressure fluid transport across the RPE presence of the vitreous physical closeness between the two entities RPE microvilli and the rod and cone outer segments interphotoreceptor matrix (IPM ) 12/07/2010EC. MuezA 48
Retinal detachment Separation RPE cells and the photoreceptors because no intercellular junctions join these cells. The RPE cells remain attached the choroid separates the photoreceptors from their blood supply, the layers are not repositioned quickly, the affected area will necrose. Anargon laser often is used to photocoagulate the edges of the detachment, producing scar tissue. This photocoagulation prevents the detachment from enlarging and facilitates the repositioning of the photoreceptors. 12/07/2010EC. MuezA 49
3.External limiting membrane (ELM). 12/07/2010EC. MuezA 50 Not a true membrane formed by attachment of photoreceptors and M端ller cells highly fenestrated. Extents from the ora serrata to the edge of optic disc. Main function- Selective barrier for nutrients Stabilization of transducing portion of the photoreceptors. 4. Outer nuclear layer formed by nuclei of rods and cones. Rod nuclei form the bulk of this layer.
5.The outer plexiform layer (OPL) Synaptic junction of photoreceptor and the horizontal and bipolar cells. In the fovea there is no synaptic because cone pedicles are displaced laterally to the extrafoveal region. At the edge of the foveola, it lies almost parallel to the internal limiting membrane. marks the junction of the end organs of vision and first order neurons in retina Function Transmission and amplification of electrical potential The presence of numerous junctions-Aids in the homeostasis of the retina. Act as a functional barrier to diffusion of fluids and metabolites dark maroon dot and blot hemorrhage in deep retinal hemorrhage 12/07/2010EC. MuezA 51
6.The inner nuclear layer (INL) Located betweeen OPL and IPL Consists of following 8-12 rows of cells: 4 nucli Bipolar cells- 9 types Horizontal- 3 types(H1,H11,H111) Amacrine Supportive Mullers cells for transduction and amplification of light signal The retinal blood vessels ordinarily do not extend beyond this point. 12/07/2010EC. MuezA 52
7.The inner plexiform layer (IPL) Synapses bet. Axons of bipolar cells and dendrites of ganglion and amacrine cells. The bipolar cell contracts two processes, one from a ganglion cell and the other from an amacrine cell 8. The nerve fiber layer (NFL) Formed by axons of the ganglion cells. Normally, these axons do not become myelinated until they pass through the lamina cribrosa of the optic nerve 12/07/2010EC. MuezA 53
Overall, cells and their processes in the retina oriented perpendicular to the RPE in the middle and outer but parallel to the retinal surface in the inner layers. For this reason, deposits of blood or exudates form round blots in the outer layers (where small capillaries are found) linear or flame-shaped patterns in the nerve fiber layer. At the fovea, the outer layers also tend to be parallel to the surface (Henle fiber layer). radial or star-shaped patterns form 12/07/2010EC. MuezA 54
Arrangement of nerve fiber in the Retina Fibres from the nasal half superior and inferior radiating fibres (srf andirf). Fibres from the macular regiontemporal part of the disck as papillomacular bundle (pmb). Fibres from the temporal retina arch above and below the macular and papillomacular bundle as superior and inferior arcuate fibres (saf and iaf) with a horizontal raphe in between. The nerve fibre layer is thickest at the nasal edge of the disc, where it measures 20-30 microns decreased with increasing distance from the disc margin 8 to 11 microns just posterior to the ora serrata The papillomacular bundle represents the thinnest portion of the nerve fibre layer around the optic disc 12/07/2010EC. MuezA 55
ARRANGEMENT OF NERVE FIBRES OF THE OPTIC NERVE HEAD Fibres form the peripheral part of the retina lie deep in the retina but superficial part of the optic disc. fibres originating closer to the optic nerve head lie superficially in the retina central (deep) portion of the disc. 12/07/2010EC. MuezA 56
THICKENSS OF NERVE FIBRE LAYER AT THE DISC: Thickness of the nerve fibre layer around the different quadrants of the optic disc margin progressively increasing order: Most lateral quadrant (thinnest) Upper temporal and lower temporal quadrant Most medial quadrant Upper nasal and lower nasal quadrant (thickest) 12/07/2010EC. MuezA 57
Clinical significance Papilloedema appears first in the thickest quadrant (upper nasal and lower nasal) last of all in the thinnest quadrant (most lateral). Arcuate nerve fibres which occupy the superior temporal and inferior temporal quadrants most sensitive to glaucomatous damage Macular fibres occupying the lateral quadrant most resistant to glaucomatous damage retention of the central vision till end The loss of tissue seems to be associated with compaction and fusion of the laminar plates 12/07/2010EC. MuezA 58
9. internal limiting membrane innermost layer of the retina and the outer boundary of the vitreous Both the retina and the vitreous contribute Collagen fibrils proteoglycans (mostly hyaluronic acid) of the vitreous; the basement membrane; the plasma membrane of the Muller cells and possibly other glial cells of the retina It continues uninterrupted at the fovea where it is thickest At the periphery of the retina, the membrane is continuous with the basal lamina of the ciliary epithelium It gives the posterior retina a characteristic sheen when observed with the ophthalmoscope 12/07/2010EC. MuezA 59
Retina blood suplay The outer retinal layers receive nutrition from the choroidal capillary bed The central retinal artery provides nutrients to the inner retinal layers. The artery enters the retina through the optic disc slightly nasal of center, and branches into a superior and inferior nasal and temporal branches, and continue to bifurcate The nasal branches run a relatively straight course toward the ora serrata, but the temporal vessels arch around the macular area en route to the periphery. located in the nerve fiber layer just below the transparent internal limiting membrane 12/07/2010EC. MuezA 60
12/07/2010EC. MuezA 61
A capillary-free zone 0.5 mm in diameter is free of all retinal vessels. Retinal blood vessels lack an internal elastic lamina & a continuous layer of smooth muscle cells. Retinal vessels are said to be end vessels because they do not anastomose with any other system of blood vessels. Retinal vessels terminate in delicate capillary arcades approximately 1 mm from the ora serrata. The retinal capillaries are made up of a single layer of unfenestrated endothelium The endothelial cells are one part of the blood-retinal barrier because they are joined by zonula occludens. 12/07/2010EC. MuezA 62
Two capillary networks are formed. The deep capillary network lies in the inner nuclear layer near the outer plexiform layer The superficial capillary network is in the nerve fiber layer or ganglion cell layer. The retina outer to the outer plexiform layer is avascular The outer plexiform layer is thought to receive its nutrients from both retinal and choroidal vessels. The middle limiting membrane usually is regarded as the border between the choroidal and retinal supplies. 12/07/2010EC. MuezA 63
A dense peripapillary network of capillaries, radially arranged around the optic nerve head, follows the arcuate course of the nerve fibers as they enter the disc. A cilioretinal artery is a vessel that enters the retina from the edge of the disc origin in the choroidal vasculature. nourishes the macular area, is found in approximately 15% to 20% of the population A cilioretinal artery can maintain the viability of the macula if blockage of the central retinal artery occurs. 12/07/2010EC. MuezA 64
Fundus view of vessels The retinal blood vessels are readily visible with the ophthalmoscope, and because the vessel walls are transparent, the clinician actually is seeing the column of blood within the vessel. The lighter-colored blood is the oxygenated blood of the artery the venous deoxygenated blood is slightly darker. The artery generally lies superficial to the vein. With aging and some disease processes, such as hypertension, the arterial wall may thicken and constrict the vein; this is called arteriovenous nicking. In some individuals the pigmented choroid and it svessels are visible through the retina, and the choroidal vessels appear as flattened ribbons 12/07/2010EC. MuezA 65
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Anatomy of the Retina.pptx

  • 1. 12/07/2010EC. MuezA 1 Anatomy of the Retina Presenter; Muez A. (1st year Ophthalmology Resident) Moderator; Dr Demoze (Consultant vitreoretinal Surgeon)
  • 2. Out line Introduction Gross anatomy Embryology Microscopic anatomy Blood supply 12/07/2010EC. MuezA 2
  • 3. Introduction Inner posterior 2/3rd of the eye ball Continuous posteriorly as optic nerve, anteriorly with the ciliary body Bordered by the vitreous internally & the Bruchs membrane externally It has pigment epithelium and neural layer Surface area of about 266 mm2 Thickest in the papillomacular bundle near the optic nerve (0.23 mm) thinnest in the foveola (0.10 mm) and ora serrata (0.11 mm). Site of transformation of light energy into a neural signal. 12/07/2010EC. MuezA 3
  • 4. Gross anatomy The major landmarks of the retina The area centralis The peripheral retina The optic disc The retinal blood vessels 12/07/2010EC. MuezA 4
  • 5. Central Retina Rich in cones, has more ganglion cells per area than elsewhere Small portion of the entire retina. 1. Foveola 2. Fovea 3. Para fovea 4. Perifovea 5. Macula Clinical function Fine visual acuity Photopic vision Stereopsis Color vision 12/07/2010EC. MuezA 5
  • 6. Macula Demarcated by superior and inferior temporal arterial arcuate Dark area in the central retina Elliptical shape horizontally Average diameter of about 5.5 mm/3.5DD 15-18属 of visual field Protects central vision by following characteristics; Highly pigmented tall epithelial cells of RPE(highest pigmentation ) reduce scattering of light The choroidal capillary bed also is thickest in the macula Highest concentration of xanthophyll pigments Act as filters, absorbs short wavelength visible light to reduce chromatic aberration Antioxidant effect Protective role against UVR damage. 12/07/2010EC. MuezA 6
  • 8. FOVEA center of macula Diameter of 1.5-1.85mm/1DD Represents 5属 of the visual field Central depression foveola The inner nuclear layer and ganglion cell layer are displaced laterally and accumulate on the curved walls of the fovea called Clivus The fovea has the highest concentration of cones (199,000-300,000 cones/mm) The photoreceptor fibers(cones) become longer as they deviate away from the center; these fibers are called Henles fibers 12/07/2010EC. MuezA 8
  • 9. Foveola Central depression in the fovea 1属 of visual field 0.35mm in D/0.3-0.4DD Six layers present in the foveola Internal limiting membrane Henles fiber layers ONL External limiting membrane Photoreceptor layers RPE form sharpest vision and steoropsis Umbo (Center of foveola) corresponds to light reflex Foveal reflex is due to the parabolic shape formed by the clivus. Loss of foveal reflux implies disruption of neural layers 12/07/2010EC. MuezA 9
  • 10. Clinical correlates; Lack of blood vessels and neural tissue in foveola allows light to pass unobstructed into the photoreceptor outer segment Chronic retinal oedema may result in the deposition of hard exudates around the fovea in the layer of Henle with a macular star configuration 12/07/2010EC. MuezA 10
  • 12. Rods reduces and are replaced by malformed cones The nuclear layers merge with the plexiform layers, Finally, neural retina becomes a single layer of irregular columnar cells that continue as the nonpigmented epithelium of the ciliary body. TheRPE is continuous with the outer pigmented epithelium of the ciliary body, the internal limiting membrane continues as the internal limiting membrane of the ciliary body. 12/07/2010EC. MuezA 12
  • 13. Ora Serrata The ora serrata is the boundary between the retina and the pars plana. A firm attachment between the retina and vitreous Its distance from the Schwalbe line is between 5.75 mm nasally and 6.50 mm temporally. In myopia, this distance is greater; in hyperopia, it is shorter. The Bruch membrane extends anteriorly, beyond the ora serrata, but is modified because there is no choriocapillaris in the ciliary body 12/07/2010EC. MuezA 13
  • 14. Topographically, the ora serrata is relatively smooth temporally and serrated nasally. Retinal blood vessels end in loops before reaching the ora serrata. The ora serrata is in a watershed zone between the anterior and posterior vascular systems peripheral retinal degeneration is relatively common. The photoreceptors are malformed, and the overlying retina frequently appears cystic (Blessing Iwanoff cysts) 12/07/2010EC. MuezA 14
  • 17. PERIPHERAL RETINAL DEGENERATION Cystic spaces and atrophied areas often are found in peripheral retina and their incidence increases with age. poor blood supply in the extreme retinal periphery. others might predispose the affected dilated fundus examinations. 12/07/2010EC. MuezA 17
  • 19. cont. The number of nerve fibers appears to be positively correlated with the size of the optic nerve head larger discs have relatively more fibers than smaller discs Smaller discs may demonstrate optic nerve head crowding. Fiber number decreases with age. The pale-yellow or salmon color of the optic disc is a combination of the scleral lamina cribrosa and the capillary network. 12/07/2010EC. MuezA 19
  • 21. Optic DISC ASSESSMENT The color of the disc configuration and depth of the physiologic cup cup-to-disc ratio appearance of the rim tissue disc borders are assessed during an ocular health examination. 12/07/2010EC. MuezA 21
  • 24. Retinal pigment epithelium The first retinal layer to be formed (3-4 month) the earliest pigmentation evident in the embryo one cell thick, the cells are cuboidal to columnar in shape the base of each cell is external toward the developing choroid the apex internal toward the inner layer of the optic cup 12/07/2010EC. MuezA 24
  • 25. The neural retina week 7, cell migration occurs, forming the inner and outer neuroblastic layers Outer neuroblastic layer differentiates to photo receptor cells,bipollar cells and horizontal cells (outer plexiform) Inner neuroblastic layer differentiates to Ganglion cell, amacrine, and M端ller cells (inner plexiform layer) The photoreceptor cells are the last cells of neural retina to differentiate (5th month) Differentiation of the neural retinal cells begins in central retina and proceeds to the periphery The Muller cells forms the internal limiting membrane 12/07/2010EC. MuezA 25
  • 26. 6 months dense accumulation of nuclei in the macular area makes this region thicker than the rest of the retina the ganglion axons from the periphery take an arched route above and below the macular area to reach the nerve head. Foveal development consists of three stages (1) displacement of inner retinal components to form the depression; (2) migration of photoreceptors toward the center, which increases cone packing (3) maturation of the photoreceptors. At 7month the ganglion and inner nuclear layer cells begin to move to the periphery of the macula. By 4 months postpartum, both these layers are displaced 12/07/2010EC. MuezA 26
  • 27. The foveal depression continues to deepen until about age 15 months The foveola, the retinal area of sharpest visual acuity, is the last to reach maturity. migration of the cones centrally, increasing cone density. The cone inner fibers elongate and adopt an oblique orientation (forming Henles fiber layer) in order to synapse with the cells of the inner nuclear layer, which have been displaced to the sloping walls 12/07/2010EC. MuezA 27
  • 28. CLINICAL COMMENT: COLOBOMA Incomplete closure of the optic fissure may affect The developing optic cup or stalk and the adult derivations of these structures, resulting in an inferior nasal defect in the optic disc, retina, ciliary body, or iris. 12/07/2010EC. MuezA 28
  • 31. 1.Retinal pigment Epithelium 4-8 million cells firmly attached to its basal lamina Single cell thick and consists of pigmented hexagonal cells Columnar in the area of the posterior pole densely pigmented in the macular area. Larger and more cuboidal less pigmented as the layer nears the ora serrata, Phagocytic cells 12/07/2010EC. MuezA 31
  • 32. Contain numerous melanosomes,pigment granules Pigment density differs in various parts of the retina Densest at the macula and at the equator decreased transmission of choroidal fluorescence observed during fundus fluorescein angiography Lipofuscin granules arise from the discs of photoreceptor outer segments and represent residual bodies arising from phagosomal activity This so-called wear-and-tear pigment less electron dense than the melanosomes increases gradually with age. 12/07/2010EC. MuezA 32
  • 33. Other material are excreted beneath the basal lamina of the RPE formation of drusen( accumulations of this extracellular material) can vary in size and are commonly classified by their funduscopic appearance as either hard or soft. located between the basement membrane of the RPE cells and the inner collagenous zone of the Bruch membrane. 12/07/2010EC. MuezA 33
  • 34. RPE - Cell Surfaces characteristics Clinical significances; No specialized junctional complex between RPE and photoreceptors- loosely adhered Potential space exists (subretinal space)- prone for RD) 34 Apical surface Has microvillous processes- Increases Surface area Interdigitate with outer segments of photoreceptor cells Contains melanin granules more dense in macular region 1.Apical surface inner surface 2.Paracellular (lateral) surface-intercellular surfaces 3.Basal surface outer surface
  • 35. Paracellular surface; Contains tight junction( Zonula Occluden & adheran, gap junctions) Junctional complex form blood-retinal barrier Maintains retinal homeostasis and prevents from toxic damages 35 Basal surface; Attached to its basal lamina, the lamina vitrea of Bruch's membrane. Nutrients from choriocapillaries difusess to RPE through basal lamina
  • 36. Sensory neural retina Transparent layer Contains 3 basic cell types photoreceptor cells Rods and cons120 million vs 6 million respectively Constitutes the outer nuclear layer and the outer plexiform layer. Neuronal cells Bipolar cells Horizontal cells 1st order neurons Amacrine cells Ganglion cells 2nd order neurons Glial cells Muller cells Astrocytes Microglial cells 12/07/2010EC. MuezA 36
  • 37. M端ller cells are large neuroglial cells that extend much of the retina. Supportive role, and providing structure Fill in most of the space of the retina not occupied by neuronal elements Ensheathe dendritic processes within the synaptic layers, providing insulation from electrical and chemical activation, Involved in glucose metabolism by synthesizing and storing glycogen Buffer in regulating concentrations of potassium ions (K+),GABA, and glutamate in the extracellular space. Apex in the photoreceptor layer, basal aspect is at the inner retinal surface Apical villi, fiber baskets (of Schultze), terminate between the inner segments of the photoreceptors. 12/07/2010EC. MuezA 37
  • 39. Microglial cells are wandering phagocytic cells found anywhere in the retina. increases in response to tissue inflammation and injury. Astrocytes star-shaped fibrous cells found in inner retina, usually in the nerve fiber and ganglion cell layers. perivascular cells form an irregular supportive network encircles nerve fibers and retinal capillaries. contribute to the internal limiting membrane Amacrine cells No axons. Stimulated by the Bipolar cells & then they excite the Ganglion cells 12/07/2010EC. MuezA 39
  • 40. Bipolar cells First order neuron in the visual pathway. Its dendrite synapses with photoreceptor and horizontal cells Axon synapses with ganglion and amacrine cells Eleven types of bipolar cells have been classified on the basis of morphology, physiology, and dendritic contacts with photoreceptors Horizontal Cells They have one long & several short processes. Inhibitory function by releasing GABA. highest concentration in fovea Modulate and transform visual information received from the photoreceptors Have a role in sharpening contrast 12/07/2010EC. MuezA 40
  • 41. Ganglion cells 2nd order neurons W cells project to the midbrain, carrying information for the pupillary response and reflexive eye movements. Y cells project to the lateral geniculate body, with some having collateral branches that travel to the midbrain, perhaps with pupillary information X cells primarily respond in visual discrimination and project to the lateral geniculate body P ganglion cells ; color vision stereopsis M ganglion cells ; rapidly to moving or changing stimuli. 12/07/2010EC. MuezA 41
  • 42. 2. Photoreceptors CONES 4_8 million cells density is maximum at fovea (199 000 cones/mm2) -minimum density- periphery light sensitive molecule Iodopsin ( color vision- photopic vision) ( 3 types of iodopsin trichromatic pigments 1. S wavelength cones- 440nm blue light) 2.M wavelenght cone- 540nm green 3. L wavelenght cone- 577nm red RODES 100-130 million cells maximum density in 20属(3mm) from the fovea(160,000 rods/mm2) rod-free at the fovea ; 0.35 mm minimum density periphery light sensitive molecule- rhodopsin ( night vision- scotopic vision) rhodopsin is sensitive to blue-green light- 493nm Main for white and black Clinical notes Mutation of rhodopsin in retinitis pigmentosa With advanced of age there is progressive loss of photoreceptors (rods are affected more than cone) poor night vision in elderly 12/07/2010EC. MuezA 42
  • 43. Morphology of Photoreceptors Rods and cones have six main parts 1. The outer segment, containing the visual pigment molecules for the conversion of light into a neural signal 2. A connecting stalk, the cilium(cytoplasmic isthmus) 3. The inner segment, containing the metabolic apparatus; 4. The outer fiber; 5. The cell body- forms outer nucleated layers 6. The inner fiber, which ends in a synaptic terminal outer plexiform layer 12/07/2010EC. MuezA 43
  • 45. the outer segments of the rods and cones difference. Rod discs are not attached to the cell membrane Cone discs are attached to the cell membrane renewed by membranous replacement. cone synaptic body, or pedicle, is more complex than the rod spherule. Cone pedicles synapse with other rods and cones as well as with horizontal and bipolar cell processes. Foveal cones have cylindrical inner segments similar to rods but otherwise are cytologically identical to extrafoveal cones. 12/07/2010EC. MuezA 45
  • 46. The Rods The most light sensitive cells Components of disc membranes are produced in the inner segment Discs contain 90% of the visual pigment remaining is scattered on plasma membrane. move along the connecting stalk to be discs at the outer segment The discs gradually displaced outward and form new discs and sloughed off and phagocytosed the rod outer segment renewal system shed regularly, with mostly occurring in the early morning. The inner fiber extends from the cell body and terminates in structure called a spherule The spherule forming a synaptic complex with bipolar dendrites and horizontal cell Rods release the neurotransmitter glutamate 12/07/2010EC. MuezA 46
  • 47. Cones The cone outer segment is shorter Dont not reach the RPE layer. Tubular processes protrude from the apical surface of the epithelial cell to surround the cone outer segment Cone at periphery is short but in central fovea it is tall and resembles rod As with rods, cones use glutamate for aneurotransmitter. 12/07/2010EC. MuezA 47
  • 48. The photoreceptor cell layer and the RPE layer. Passive forces intraocular pressure (IOP) osmotic pressure fluid transport across the RPE presence of the vitreous physical closeness between the two entities RPE microvilli and the rod and cone outer segments interphotoreceptor matrix (IPM ) 12/07/2010EC. MuezA 48
  • 49. Retinal detachment Separation RPE cells and the photoreceptors because no intercellular junctions join these cells. The RPE cells remain attached the choroid separates the photoreceptors from their blood supply, the layers are not repositioned quickly, the affected area will necrose. Anargon laser often is used to photocoagulate the edges of the detachment, producing scar tissue. This photocoagulation prevents the detachment from enlarging and facilitates the repositioning of the photoreceptors. 12/07/2010EC. MuezA 49
  • 50. 3.External limiting membrane (ELM). 12/07/2010EC. MuezA 50 Not a true membrane formed by attachment of photoreceptors and M端ller cells highly fenestrated. Extents from the ora serrata to the edge of optic disc. Main function- Selective barrier for nutrients Stabilization of transducing portion of the photoreceptors. 4. Outer nuclear layer formed by nuclei of rods and cones. Rod nuclei form the bulk of this layer.
  • 51. 5.The outer plexiform layer (OPL) Synaptic junction of photoreceptor and the horizontal and bipolar cells. In the fovea there is no synaptic because cone pedicles are displaced laterally to the extrafoveal region. At the edge of the foveola, it lies almost parallel to the internal limiting membrane. marks the junction of the end organs of vision and first order neurons in retina Function Transmission and amplification of electrical potential The presence of numerous junctions-Aids in the homeostasis of the retina. Act as a functional barrier to diffusion of fluids and metabolites dark maroon dot and blot hemorrhage in deep retinal hemorrhage 12/07/2010EC. MuezA 51
  • 52. 6.The inner nuclear layer (INL) Located betweeen OPL and IPL Consists of following 8-12 rows of cells: 4 nucli Bipolar cells- 9 types Horizontal- 3 types(H1,H11,H111) Amacrine Supportive Mullers cells for transduction and amplification of light signal The retinal blood vessels ordinarily do not extend beyond this point. 12/07/2010EC. MuezA 52
  • 53. 7.The inner plexiform layer (IPL) Synapses bet. Axons of bipolar cells and dendrites of ganglion and amacrine cells. The bipolar cell contracts two processes, one from a ganglion cell and the other from an amacrine cell 8. The nerve fiber layer (NFL) Formed by axons of the ganglion cells. Normally, these axons do not become myelinated until they pass through the lamina cribrosa of the optic nerve 12/07/2010EC. MuezA 53
  • 54. Overall, cells and their processes in the retina oriented perpendicular to the RPE in the middle and outer but parallel to the retinal surface in the inner layers. For this reason, deposits of blood or exudates form round blots in the outer layers (where small capillaries are found) linear or flame-shaped patterns in the nerve fiber layer. At the fovea, the outer layers also tend to be parallel to the surface (Henle fiber layer). radial or star-shaped patterns form 12/07/2010EC. MuezA 54
  • 55. Arrangement of nerve fiber in the Retina Fibres from the nasal half superior and inferior radiating fibres (srf andirf). Fibres from the macular regiontemporal part of the disck as papillomacular bundle (pmb). Fibres from the temporal retina arch above and below the macular and papillomacular bundle as superior and inferior arcuate fibres (saf and iaf) with a horizontal raphe in between. The nerve fibre layer is thickest at the nasal edge of the disc, where it measures 20-30 microns decreased with increasing distance from the disc margin 8 to 11 microns just posterior to the ora serrata The papillomacular bundle represents the thinnest portion of the nerve fibre layer around the optic disc 12/07/2010EC. MuezA 55
  • 56. ARRANGEMENT OF NERVE FIBRES OF THE OPTIC NERVE HEAD Fibres form the peripheral part of the retina lie deep in the retina but superficial part of the optic disc. fibres originating closer to the optic nerve head lie superficially in the retina central (deep) portion of the disc. 12/07/2010EC. MuezA 56
  • 57. THICKENSS OF NERVE FIBRE LAYER AT THE DISC: Thickness of the nerve fibre layer around the different quadrants of the optic disc margin progressively increasing order: Most lateral quadrant (thinnest) Upper temporal and lower temporal quadrant Most medial quadrant Upper nasal and lower nasal quadrant (thickest) 12/07/2010EC. MuezA 57
  • 58. Clinical significance Papilloedema appears first in the thickest quadrant (upper nasal and lower nasal) last of all in the thinnest quadrant (most lateral). Arcuate nerve fibres which occupy the superior temporal and inferior temporal quadrants most sensitive to glaucomatous damage Macular fibres occupying the lateral quadrant most resistant to glaucomatous damage retention of the central vision till end The loss of tissue seems to be associated with compaction and fusion of the laminar plates 12/07/2010EC. MuezA 58
  • 59. 9. internal limiting membrane innermost layer of the retina and the outer boundary of the vitreous Both the retina and the vitreous contribute Collagen fibrils proteoglycans (mostly hyaluronic acid) of the vitreous; the basement membrane; the plasma membrane of the Muller cells and possibly other glial cells of the retina It continues uninterrupted at the fovea where it is thickest At the periphery of the retina, the membrane is continuous with the basal lamina of the ciliary epithelium It gives the posterior retina a characteristic sheen when observed with the ophthalmoscope 12/07/2010EC. MuezA 59
  • 60. Retina blood suplay The outer retinal layers receive nutrition from the choroidal capillary bed The central retinal artery provides nutrients to the inner retinal layers. The artery enters the retina through the optic disc slightly nasal of center, and branches into a superior and inferior nasal and temporal branches, and continue to bifurcate The nasal branches run a relatively straight course toward the ora serrata, but the temporal vessels arch around the macular area en route to the periphery. located in the nerve fiber layer just below the transparent internal limiting membrane 12/07/2010EC. MuezA 60
  • 62. A capillary-free zone 0.5 mm in diameter is free of all retinal vessels. Retinal blood vessels lack an internal elastic lamina & a continuous layer of smooth muscle cells. Retinal vessels are said to be end vessels because they do not anastomose with any other system of blood vessels. Retinal vessels terminate in delicate capillary arcades approximately 1 mm from the ora serrata. The retinal capillaries are made up of a single layer of unfenestrated endothelium The endothelial cells are one part of the blood-retinal barrier because they are joined by zonula occludens. 12/07/2010EC. MuezA 62
  • 63. Two capillary networks are formed. The deep capillary network lies in the inner nuclear layer near the outer plexiform layer The superficial capillary network is in the nerve fiber layer or ganglion cell layer. The retina outer to the outer plexiform layer is avascular The outer plexiform layer is thought to receive its nutrients from both retinal and choroidal vessels. The middle limiting membrane usually is regarded as the border between the choroidal and retinal supplies. 12/07/2010EC. MuezA 63
  • 64. A dense peripapillary network of capillaries, radially arranged around the optic nerve head, follows the arcuate course of the nerve fibers as they enter the disc. A cilioretinal artery is a vessel that enters the retina from the edge of the disc origin in the choroidal vasculature. nourishes the macular area, is found in approximately 15% to 20% of the population A cilioretinal artery can maintain the viability of the macula if blockage of the central retinal artery occurs. 12/07/2010EC. MuezA 64
  • 65. Fundus view of vessels The retinal blood vessels are readily visible with the ophthalmoscope, and because the vessel walls are transparent, the clinician actually is seeing the column of blood within the vessel. The lighter-colored blood is the oxygenated blood of the artery the venous deoxygenated blood is slightly darker. The artery generally lies superficial to the vein. With aging and some disease processes, such as hypertension, the arterial wall may thicken and constrict the vein; this is called arteriovenous nicking. In some individuals the pigmented choroid and it svessels are visible through the retina, and the choroidal vessels appear as flattened ribbons 12/07/2010EC. MuezA 65
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Editor's Notes

  • #37: Neuroglial cells, although not actively involved in the transfer of neural signals, provide structure and support and play a role in the neural tissue reaction to injury or infection. Types of neuroglial cells found in the retina include M端ller cells, microglial cells, and astrocytes.