The 411 on optic nerves

The Optic Nerve

The two optic nerves are the connections between the eyes and the rest of the brain, and all visual information passes through them. The optic disc--the part of the optic nerve that a doctor sees when he looks into an eye--is 1.5-2.0 mm in diameter—only about 1/16th of an inch.

Disorders of the optic nerve are called optic neuropathies. The commonest optic neuropathy is glaucoma, characteristically a disease where damage to the nerve is produced by elevated pressure inside the eye. The damage can be prevented or arrested by lowering intraocular pressures by medications or surgery. There are literally dozens of other disorders that can affect these important structures.

Inflammation produces optic neuritis, which usually presents as sudden visual loss and pain on eye movement. There is no known effective treatment, but vision usually spontaneously improves over weeks or months. Because optic neuritis may be associated with inflammation in other parts of the brain, magnetic resonance imaging is obtained. ( this sounds a lot like whats going down, i'm having my magnetic resonance imaging tomorrow)

Another disorder that presents as sudden visual loss is ischemic optic neuropathy, a problem with the circulation to the optic nerve. In older persons this may be a sign of a generalized inflammation of blood vessel walls known as giant cell arteritis. Ischemic optic neuropathy itself has no known effective treatment, but giant cell arteritis should be treated with corticosteroids to prevent more blood vessels from closing off.

Another optic neuropathy that fortunately is rare in the United States is nutritional. In the early 1990’s more than 50,000 Cubans developed visual loss and other symptoms because their diets were deficient in essential B vitamins.

Infections can affect the optic nerves. A bacterial infection contracted by contact with cats leads to leakage of blood vessels in the optic nerve that spreads into the retina—neuroretinitis.

The optic nerves are also an indicator of increased pressure inside the skull. Swelling of the optic nerve, called papilledema, requires urgent evaluation as tumors, bleeding, and obstruction of cerebrospinal fluid flow known as hydrocephalus must be excluded.

Sometimes the appearance of an optic nerve is difficult to interpret. A few people have optic nerves that appear swollen, but are not. This is pseudo-papilledema. Especially in children, calcifications buried in the optic nerves known as drusen may produce pseudopapilledema. Such calcifications show up on ultrasound or CT.

A normal optic nerve is an important sign of health. Testing of the optic nerves’ function includes measurement of visual acuity, assessment of color vision, visual fields, pupillary reactions, and ophthalmoscopy (looking inside the eye with various optical instruments). Because glaucoma is a common and usually treatable disease, tonometry—determination of intraocular pressure—is part of most eye examinations.