The infratrochlear nerve is given off from the nasociliary nerve just before it enters the anterior ethmoidal foramen.
It runs forward along the upper border of the medial rectus, and is joined, near the pulley of the superior oblique, by a filament from the supratrochlear nerve.
It then passes to the medial commissure of the eye, and supplies the skin of the upper eyelids and bridge of the nose, the conjunctiva, lacrimal sac and caruncle.
Infratrochlear means "below the trochlea". The term trochlea means "pulley" in Latin. Specifically, the trochlea referred to is a bony loop at the inner and upper corner of the eye socket (trochlea of superior oblique), through which the tendon of the superior oblique muscle passes.
Nerves of the orbit. Seen from above.
This article incorporates text from a public domain edition of Gray's Anatomy.