Structure and Course
- The nasociliary nerve enters the orbit via the superior orbital fissure.
- It passes through the common tendinous ring.
- It runs between the two heads of the lateral rectus muscle.
- It runs between the superior and inferior rami of the oculomotor nerve.
- It passes across the optic nerve (CN II) along with the ophthalmic artery.
- The nasociliary nerve runs obliquely beneath the superior rectus muscle and superior oblique muscle.
- It reaches the medial wall of the orbital cavity.
- It emits the posterior ethmoidal nerve.
- It emits the anterior ethmoidal nerve.
- It provides sensory innervation to structures surrounding the eye.

Branches
- The branches of the nasociliary nerve include the posterior ethmoidal nerve.
- The branches of the nasociliary nerve include the anterior ethmoidal nerve.
- The branches of the nasociliary nerve include the long ciliary nerves.
- The branches of the nasociliary nerve include the infratrochlear nerve.
- The branches of the nasociliary nerve include the communicating branch to the ciliary ganglion.

Function
- The branches of the nasociliary nerve provide sensory innervation to the cornea.
- The branches of the nasociliary nerve provide sensory innervation to the eyelids.
- The branches of the nasociliary nerve provide sensory innervation to the conjunctiva.
- The branches of the nasociliary nerve provide sensory innervation to the ethmoid air cells.
- The branches of the nasociliary nerve provide sensory innervation to the mucosa of the nasal cavity.

Clinical Significance
- The integrity of the nasociliary nerve can be tested by examining the corneal reflex.
- The short and long ciliary nerves carry the afferent limb of the corneal reflex.
- If neither eye blinks when the cornea is irritated, the nasociliary nerve may be damaged.
- If only the contralateral eye blinks, the ipsilateral facial nerve may be damaged.
- If only the ipsilateral eye blinks, the contralateral facial nerve may be damaged.

Summary
The nasociliary nerve is a branch of the ophthalmic division of the trigeminal nerve. It enters the orbit via the superior orbital fissure and provides sensory innervation to various structures surrounding the eye, including the cornea, eyelids, conjunctiva, ethmoid air cells, and nasal cavity. Its branches include the posterior ethmoidal nerve, anterior ethmoidal nerve, long ciliary nerves, infratrochlear nerve, and communicating branch to the ciliary ganglion. The integrity of the nasociliary nerve can be assessed through the corneal reflex, and damage to the nerve can result in impaired blinking responses.

Nasociliary nerve (Wikipedia)

The nasociliary nerve is a branch of the ophthalmic nerve (CN V₁) (which is in turn a branch of the trigeminal nerve (CN V)). It is intermediate in size between the other two branches of the ophthalmic nerve, the frontal nerve and lacrimal nerve.

Nasociliary nerve
Nerves of the orbit, and the ciliary ganglion. Side view. (Nasociliary is at center.)
Nerves of septum of nose. Right side. (Nasociliary is rightmost yellow line.)
Details
From	Ophthalmic nerve
To	posterior ethmoidal nerve, anterior ethmoidal nerve, long ciliary nerves, infratrochlear nerve, communicating branch to ciliary ganglion
Identifiers
Latin	nervus nasociliaris
TA98	A14.2.01.025
TA2	6204
FMA	52668
Anatomical terms of neuroanatomy [edit on Wikidata]