Lacrimal nerve

The lacrimal nerve is the smallest of the three main branches of the ophthalmic nerve (CN V1) (itself a branch of the trigeminal nerve (CN V)).  

It enters the orbit outside the common tendinous ring and passes forward along the side wall of the orbit.

It provides sensory innervation to the skin and both surfaces of conjunctiva at the lateral portion of the upper eyelid.

It also receives a parasympathetic secretomotor communicating branch for the lacrimal gland which it conveys to the gland.

Origin
The lacrimal nerve branches from the ophthalmic nerve immediately before traveling through the superior orbital fissure to enter the orbit.

At the superior portion of the lateral wall of the orbit, it also receives a secretomotor  communicating  parasympathetic branch from the zygomaticotemporal nerve  for the lacrimal gland. 

Course
It enters the orbit through the superior orbital fissure outside (lateral to ) the common tendinous ring, coursing lateral to the frontal nerve and trochlear nerve (CN IV). Once inside the orbit, it travels anteriorly along (the superior portion of ) the lateral wall of the orbit upon the superior margin of the lateral rectus muscle;   here, it receives a secretomotor branch for the lacrimal gland from the zygomaticotemporal nerve.  It is accompanied by the lacrimal artery along its course through the orbit. It travels through the lacrimal gland, supplying the gland with sensory and parasympathetic branches, then continuing anteriorly as a few small sensory branches. It pierces the orbital septum to reach its terminal target tissues. 

Sensory
The lacrimal nerve provides sensory innervation to:


 * the lacrimal gland
 * a small area of  skin over the lateral portion of the upper eyelid  
 * both surfaces (i.e. ocular and palpebral ) of the conjunctiva at the lateral portion of the upper eyelid   (i.e. the conjunctiva at the superior fornix )
 * skin of the lateral forehead and scalp.

Parasympathetic
At the superior portion of the lateral wall of the orbit, the lacrimal nerve receives a secretomotor  communicating  parasympathetic branch (containing post-ganglionic fibres for the lacrimal gland from the pterygopalatine ganglion ) from the zygomaticotemporal nerve  which it conveys to the lacrimal gland. 

Variation
Occasionally, the lacrimal nerve is replaced by the zygomaticotemporal nerve, and vice versa.