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Optic nerve anatomy
Anatomy & Optics
Key Points
- •The optic nerve has 4 parts: intraocular (1 mm), intraorbital (25–30 mm, S-shaped), intracanalicular (6–10 mm), and intracranial (10 mm) - total ~50 mm; contains ~1.2 million RGC axons
- •The lamina cribrosa is the primary site of glaucomatous damage; myelination stops here; it is weaker superiorly and inferiorly explaining the arcuate pattern of glaucomatous field loss
- •Blood supply: optic nerve head from SPCAs + circle of Zinn-Haller (not CRA); CRA enters the nerve ~10–12 mm behind the globe and supplies the inner retina; pial plexus supplies the intraorbital segment
- •The optic nerve is a CNS tract enclosed by meninges with CSF in the subarachnoid space - raised ICP causes papilledema via CSF pressure transmission along the optic nerve sheath
- •The intracanalicular segment is most vulnerable to trauma (dura adherent to periosteum, no room for expansion); the ophthalmic artery travels through the same canal
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- Definition
- Epidemiology
- Aetiology and causes
- Pathogenesis
- Classification
- Risk factors and associations