CN II is not a true peripheral nerve but a white matter tract of the brain (surrounded by meninges and CSF, not by epineurium). Optic nerve sheath meningioma and optic glioma arise from this covering. Raised ICP produces papilloedema (optic disc swelling from CSF transmitted through the optic nerve sheath). The afferent pupillary defect (RAPD) on swinging light test indicates optic nerve dysfunction.
| Origin | Retinal ganglion cells of the eye |
|---|---|
| Course | Exits the eye at the optic disc (blind spot), passes through the optic canal of the sphenoid bone, meets the contralateral nerve at the optic chiasm (nasal fibres decussate), continues as the optic tract to the lateral geniculate nucleus of the thalamus |
| Motor |
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| Sensory |
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The relative afferent pupillary defect (Marcus Gunn pupil) is the most sensitive clinical test for unilateral optic nerve dysfunction, the affected pupil paradoxically dilates when the flashlight swings to it from the normal eye. This test detects significant optic nerve lesions before visual acuity is affected. Optic neuritis from multiple sclerosis produces RAPD, central scotoma, and colour desaturation.
CN II demyelination in MS producing unilateral visual loss, RAPD, and colour desaturation managed with IV methylprednisolone to accelerate recovery.
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