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Cranial nerves of the eye (CN III, IV, VI)
Anatomy & Optics
Key Points
- •CN III innervates SR, IR, MR, IO, LPS + parasympathetics (sphincter pupillae, ciliary muscle); divides into superior (SR + LPS) and inferior (MR + IR + IO + parasympathetics) divisions; pupil-involving palsy = suspect PComA aneurysm
- •CN IV is unique: exits dorsally, decussates completely, has the longest intracranial course (~75 mm), is the thinnest CN; innervates SO only; bilateral in ~50% of traumatic cases
- •CN VI innervates LR only; traverses Dorello's canal at the petrous apex; runs through the cavernous sinus (not in wall); CN VI palsy is a false localising sign of raised ICP
- •Cavernous sinus lateral wall (superior to inferior): CN III → IV → V1 → V2; CN VI runs through the sinus alongside the ICA; CN VI most vulnerable to cavernous sinus pathology
- •Aberrant regeneration occurs only after compressive CN III palsy (never microvascular); primary aberrant regeneration (no preceding acute palsy) → suspect cavernous sinus meningioma
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Keep reading Cranial nerves of the eye (CN III, IV, VI)
17 more sections are included with the Clinical plan.
- Definition
- Epidemiology
- Aetiology and causes
- Pathogenesis
- Classification
- Risk factors and associations