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Retinal anatomy
Anatomy & Optics
Key Points
- •The retina has 10 layers (ILM → NFL → GCL → IPL → INL → OPL → ONL → ELM → PRL → RPE): inner retina (layers 1-6) supplied by CRA (end artery); outer retina (layers 7-10) supplied by choroid - this dual supply explains the cherry-red spot in CRAO
- •Photoreceptors: ~120 million rods (scotopic, peak at 20 degrees from fovea) and ~6-7 million cones (photopic, peak at foveola ~200,000/mm2); 3 cone types: S (blue, 420 nm), M (green, 530 nm), L (red, 560 nm)
- •The fovea (1.5 mm) has NO inner retinal layers (all displaced laterally) and the foveal avascular zone (0.5 mm) has no retinal capillaries - nourished entirely by choroid; foveola (0.35 mm) is the thinnest retina (130 um, cones only)
- •RPE performs 6 critical functions: visual cycle (retinoid metabolism), phagocytosis of outer segments, outer blood-retinal barrier (tight junctions), light absorption (melanin), ion/fluid transport, and metabolic support - dysfunction → AMD, CSCR
- •Retinal ganglion cells (~1.2 million): axons form the NFL → converge at optic disc → become the optic nerve; thickest GCL at macula (8-10 cells); glaucomatous damage occurs at the lamina cribrosa; loss is irreversible
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- Definition
- Epidemiology
- Aetiology and causes
- Pathogenesis
- Classification
- Clinical features