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Anatomy of Retina
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- 2. INTRODUCTION • It’s theinternal layer of eyeball. • A thin transparent membrane having a purplish-red color. • Thickness>> 0.56mm near the optic disc to 0.1mm at the ora serrata… while it’s thinnest at the fovea centralis. • Continuous posteriorly with the optic nerve, while anteriorly with the ciliary body & iris epithelium. • Bordered by the vitreous internally & the Bruch’s membrane externally. • Firmly attached at the margins of optic disc and at its anterior termination at the ora serrata . • Approximate landmark on outside of the eye; medially insertion of medial rectus, laterally insertion of lateral rectus (closer to the limbus nasally)
- 4. • It consistsof an : -outer retinal pigment epithelium. (RPE) (derived from outer layer of optic cup). -inner neurosensory layer. (derived from inner layer of optic cup). • Macula lutea: an oval ,yellowish area ,at the center of the posterior part of retina… It has central depression called the fovea centralis. • The optic disc: a 3-mm depression of the retina where the optic nerve leaves… pierced by the central retinal artery & vein… Blind spot.
- 6. EMBRYOLOGY • • • • The outer layerof the optic cup is known as the pigmented layer of the retina. Development of the inner (neural) layer of the optic cup is more complicated. The posterior four-fifths, the pars optica retinae, contains cells bordering the intraretinal space that differentiate into light-receptive elements, rods and cones. Adjacent to this photoreceptive layer is the mantle layer, which, as in the brain, gives rise to neurons and supporting cells, including the outer nuclear layer, inner nuclear layer, and ganglion cell layer.
- 8. MICROSCOPIC STRUCTURE OFRETINA It has 10 layers: 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
- 11. RETINAL PIGMENT EPITHELIUM •Hexagonally arranged single layer of narrow & tall cells from the margin of the optic nerve flattening gradually towards the ora serrata. • The basal end of each cell is infolded and rests on a B.M which forms a part of the Bruch's membrane. • Apically shows microvili (5-7um long ), which project between & adhesively bind with rods & cones but with no specialized attachments. • The adjacent cell membrane are bound together in basal region by zonula adherens, and in apical region by zonula occludens.
- 13. NEURAL RETINA Photo receptors *Rods: -110-125 milion . - denser at the periphery (absent at fovea) - responsible for vision in dim light producing images of varying shades of black & white. *Cones: -number about 6.3-6.8milion . -highest density at the fovea -responsible for color vision in bright light.
- 16. BIPOLAR CELLS • Firstorder neuron in visual pathway. • one or more dendrites pass outward to synapse with photoreceptor cell terminal . • The single axon is directed inward to synape with ganglion cell and amacrine cells. • Types: -Rod bipolar cells: connecting rods to ganglion cells, -Flat or diffuse bipolar cell: connect cones to ganglion cells, -Midget bipolar cell: connect a single cone cell to a single midget ganglion cell.
- 17. GANGLION CELLS • Secondorder neuron in visual pathway. • Only 100 million ganglion cells in the retina; meaning more than 100 photoreceptors per ganglion cell. • Single layer in periphery and increase towards the macula while completely absent at the fovea. • Nonmyelinated intraocular & become myelinated just after leaving the lamina cribrosa. • The myelin sheath is formed by oligodendrocytes. • If intraocular part gets myelinated, it results in a blind spot.
- 19. BLOOD SUPPLY • Dualsupply: • The outer laminae (down to the outer nuclear) by the choroidal capillaries • The inner laminae by the cental retinal artery & vein • The integrity of the retina depends on both of these circulations, neither of which alone is sufficient & there’s No anastomosis.