The Anatomy of the Ophthalmic Nerve

The ophthalmic nerve is the first branch of the trigeminal nerve, which is also known as the fifth cranial nerve. The ophthalmic nerve supplies sensory innervation to the structures of the eye, including the cornea, ciliary body, lacrimal gland, and conjunctiva. It also supplies nerves to the part of the mucous membrane of the nasal cavity, and to the skin of the eyelids, eyebrow, forehead, and nose.

Anatomy

The ophthalmic nerve is purely a sensory nerve and it doesn't provide any motor function. It is the smallest division of the trigeminal nerve, which is one of the 10 cranial nerves that stem from the brain itself.

The ophthalmic nerve branches from the trigeminal nerve in the skull and begins in the lateral wall of the cavernous sinus, a cavity between the bones in the front and middle of the skull. The ophthalmic nerve lies below the oculomotor and trochlear nerves and divides into the frontal, lacrimal, and nasociliary nerves. These nerves then enter the orbital cavity (eye socket) through the superior orbital fissure. They branch out to supply the skin and mucous membranes of the front of the head and nose, as well as structures of the eye.

A map of the areas it innervates includes the forehead, front of the scalp, eyes, and anterior surface of the nose, but not the sides of the nose.

Function

The ophthalmic nerve supplies sensory fibers to the following areas:

• Face: Upper eyelid and conjunctiva, also including the eyebrow, forehead, and scalp
• Skull: Roof of the eye orbit, frontal, ethmoid, and some sinuses
• Eye: Including the cornea, iris, ciliary body, lacrimal gland, and sac

The ophthalmic nerve exchanges nerve fibers with the three motor nerves of the eye including the trochlear nerve, the oculomotor nerve, and the abducent nerve.

Associated Conditions

If the ophthalmic nerve is damaged, a person may experience symptoms related to sensory malfunctions. For example, infections of the trigeminal ganglion by the herpes zoster virus (shingles) causes painful sensations along the path of the trigeminal nerve, but mostly affects the areas innervated by the ophthalmic nerve. The infection may result in complete loss of sensation in the affected parts.

Malfunctions of the facial nerve, the sevent cranial nerve, causes a condition called Bell's palsy. This condition is usually caused by inflammation of the nerve that is in most cases caused by neurotropic viruses, such as herpes simplex virus type-1, HIV, and herpes zoster.

Supraorbital neuralgia is a rare condition that involves the ophthalmic nerve. The supraorbital nerve arises from fibers of the frontal nerve, which is the largest branch of the ophthalmic nerve. The frontal nerve branches into the supraorbital nerve and the supratrochlear nerve, which both exit the orbit anteriorly. The supraorbital nerve sends fibers to the scalp and provides sensory innervation to the forehead, upper eyelid, and anterior scalp.

Supraorbital neuralgia produces persistent pain in the supraorbital region and forehead with occasional sudden paresthesias (prickling plain) in the distribution of the supraorbital nerves. A person suffering from supraorbital neuralgia may complain of painful hair on the front of the head. Supraorbital nerve block is useful in the treatment of supraorbital neuralgia.

Treatment

Treatment and rehabilitation of problems with the ophthalmic nerve mainly depend on the treatment of the underlying condition, such as with Herpes zoster. If an antiviral is prescribed early enough—within 72 hours of onset of rash—then neuralgia is limited.

However, sometimes it's difficult for physicians to diagnose the exact underlying condition and must resort to treating the source of where the pain is stemming from. For example, since the ophthalmic nerve is an extension of the trigeminal nerve, procedures focus on changes to the trigeminal nerve or ganglion itself.

Medications

Anticonvulsants and muscle relaxants are prescribed to block the pain signals from the nerve. In severe cases, surgery may be needed.

Microvascular Decompression

This surgery works to reroute a blood vessel from pressing on the trigeminal nerve. Sometimes a Teflon sponge is placed between the blood vessel and the nerve, though studies have reported the Teflon can cause inflammation. As a last resort, sometimes the nerve is actually cut to so pain signals are stopped.

Trigeminal Plasticity

Scientists feel that this phenomenon—which allows for adjacent nerves to partially adopt the role of the main nerve and cover areas of the injured branch—may allow for some rehabilitation of nerve function after non-surgical nerve damage.

Other areas of treatment research are covering electro-stimulation, vitamins, antioxidants, alpha-lipoic acid, and neurotrophins.