The nasociliary nerve is a branch of the ophthalmic division of the trigeminal nerve (V1), entering the orbit through the superior orbital fissure within the tendinous ring. It gives off the long ciliary nerves (corneal sensation and afferent limb of the corneal reflex), communicating branch to the ciliary ganglion, posterior and anterior ethmoidal nerves, and terminates as the infratrochlear and external nasal nerves supplying the skin of the dorsal nose and medial lower eyelid.
The nasociliary nerve is the sensory nerve of the cornea and is the nerve whose stimulation produces the corneal reflex, tested clinically to assess trigeminal and facial nerve integrity. Hutchinson sign in herpes zoster, where vesicles appear on the tip and lateral side of the nose (external nasal nerve territory), indicates nasociliary nerve involvement and predicts a high risk of zoster ophthalmicus with potential corneal involvement, requiring urgent ophthalmological assessment. The nerve is anaesthetised during retrobulbar block for ocular surgery.
Reactivation of varicella-zoster virus in the nasociliary nerve produces vesicular lesions on the nose (Hutchinson sign) and risks corneal denervation, exposure keratitis, and uveitis, requiring antiviral treatment within 72 hours to limit ophthalmic complications.
Damage to the nasociliary nerve abolishes the afferent limb of the corneal reflex, eliminating the protective blink response and risking exposure keratitis and corneal ulceration, particularly dangerous in anaesthetised patients or those with facial nerve palsy.
