Nerve · Head

Nasociliary nerve

Nervus nasociliaris

The sensory nerve of the eyeball itself, and the middle branch of the ophthalmic division. Unlike its two siblings it enters the orbit inside the ring of muscle origins, then crosses above the optic nerve from the outer wall to the inner one, shedding branches as it goes: long ciliary nerves to the eyeball, the sensory root of the ciliary ganglion, the ethmoidal nerves to the nose and sinuses, and finally the infratrochlear nerve to the inner corner of the eye. It is the only branch of V1 that reaches the cornea, so it is the nerve that makes an eyelash on the eye unbearable — and it also supplies the lining of the nose, which is why a streaming eye and a tickling nose feel like one event.