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Sclera anatomy
Anatomy & Optics
Key Points
- •The sclera is composed of irregularly arranged type I collagen (→ opacity, unlike cornea's regular arrangement → transparency); thickness varies from ~0.3 mm (thinnest, behind muscle insertions) to ~1.0 mm (thickest, posterior pole near optic nerve)
- •The lamina cribrosa is a sieve-like scleral plate with 200-300 pores through which 1.2 million optic nerve axons pass - site of glaucomatous damage (posterior bowing → axon compression); myelination begins here; superior/inferior poles have largest pores (weakest → explains arcuate scotoma)
- •Scleral emissaria: posterior (optic nerve, SPCAs, LPCAs, CRA/CRV), equatorial (4-7 vortex veins), anterior (7 ACAs, aqueous veins); the scleral spur is the posterior attachment of the TM and anterior attachment of Brucke's ciliary muscle
- •Blue sclera indicates thin sclera (uveal pigment shows through): osteogenesis imperfecta (type I collagen defect), Ehlers-Danlos, Marfan, normal infants; staphyloma: scleral ectasia lined by uvea - posterior staphyloma is commonest (pathological myopia)
- •Scleritis is associated with systemic autoimmune disease in ~50%; necrotising scleritis (most severe) → scleral necrosis; scleromalacia perforans = necrotising WITHOUT inflammation (long-standing RA); posterior scleritis → B-scan 'T-sign'
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13 more sections are included with the Clinical plan.
- Definition
- Epidemiology
- Aetiology and causes
- Pathogenesis
- Classification
- Clinical features