Optic atrophy

Definition

Rhythmic, oscillating motions of the eyes are called nystagmus. The to-and-fro motion is generally involuntary. Vertical nystagmus occurs much less frequently than horizontal nystagmus and is often, but not necessarily, a sign of serious brain damage. Nystagmus can be a normal physiological response or a result of a pathologic problem.

Description

The eyes play a critical role in maintaining balance. They are directly connected to other organs of equilibrium, most important of which is the inner ear. Paired structures called the semicircular canals deep in the skull behind the ears sense motion and relay that information to balance control centers in the brain. The eyes send visual information to the same centers. A third set of sensors consists of nerve endings all over the body, particularly in joints, that detect position. All this information is integrated to allow the body to navigate in space and gravity.

It is possible to fool this system or to overload it with information so that it malfunctions. A spinning ride at the amusement park is a good way to overload it with information. The system has adapted to the spinning, expects it to go on forever, and carries that momentum for some time after it is over. Nystagmus is the lingering adjustment of the eyes to tracking the world as it revolves around them.

Nystagmus can be classified depending upon the type of motion of the eyes. In pendular nystagmus the speed of motion of the eyes is the same in both directions. In jerk nystagmus there is a slow and fast phase. The eyes move slowly in one direction and then seem to jerk back in the other direction.

Nystagmus can be present at birth (congenital) or acquired later on in life. A certain type of acquired nystagmus, called spasmus nutans, includes a head tilt and head bobbing and generally occurs between four to 12 months of age. It may last a few months to a few years, but generally goes away by itself.

Railway nystagmus is a physiological type of nystagmus. It happens when someone is on a moving train (thus the term railway) and is watching a stationary object which appears to be going by. The eyes slowly follow the object and then quickly jerk back to start over. Railway nystagmus (also called optokinetic nystagmus) is a type of jerk nystagmus. This phenomenon can be used to check vision in infants. Nystagmus can also be induced by fooling the semicircular canals. Caloric stimulation refers to a medical method of testing their connections to the brain, and therefore to the eyes. Cold or warm water flushed into the ear canal will generate motion signals from the inner ear. The eyes will respond to this signal with nystagmus if the pathways are intact.

Causes & symptoms

There are many causes of nystagmus. Nystagmus may be present at birth. It may be a result of the lack of development of normal binocular fixation early on in life. This can occur if there is a cataract at birth or a problem is some other part of the visual system. Some other conditions that nystagmus may be associated with include:

• Albinism. This condition is caused by a decrease in pigmentation and may affect the eyes.
• Disorders of the eyes. This may include optic atrophy, color blindness, very high nearsightedness (myopia) or severe astigmatism, or opacities in the structures of the eyes.
• Acute labyrinthitis. This is an inflammation in the inner ear. The patient may have dizziness (vertigo), nausea and vomiting, and nystagmus.
• Brain lesions. Disease in many parts of the brain can result in nystagmus.
• Alcohol and drugs. Alcohol and some medications (e.g., anti-epilepsy medications) can induce or exaggerate nystagmus.
• Multiple sclerosis. A disease of the central nervous system.

Diagnosis

Nystagmus is a sign, not a disease. If abnormal, it indicates a problem in one of the systems controlling it. An ophthalmologist and/or neuro-ophthalmologist should be consulted.

Treatment

There is one kind of nystagmus that seems to occur harmlessly by itself. The condition, benign positional vertigo, produces vertigo and nystagmus when the head is moved in certain directions. It can arise spontaneously or after a concussion. Motion sickness medicines sometimes help. But the reaction will dissipate if continuously evoked. Each morning a patient is asked to produce the symptom by moving his or her head around until it no longer happens. This prevents it from returning for several hours or the entire day.

Prisms, contact lenses, eyeglasses, or eye muscle surgery are some possible treatments. These therapies may reduce the nystagmus but may not alleviate it. Again, because nystagmus may be a symptom, it is important to determine the cause.

Key Terms

Binocular fixation

Both eye pointed to and looking at the same object.

Cataract

A clouding of the lens of the eye.

Optic atrophy

Degeneration of the optic nerve.

Semicircular canals

Structures of the inner ear that help in maintaining balance.

Vertigo

A sense of spinning usually accompanied by unsteadiness and nausea.

Further Reading

For Your Information

Books

• Horton, Jonathan C. "Disorders of the Eye." Harrison's Principles of Internal Medicine, 14th edition, edited by Kurt Isselbacher et al. New York: McGraw-Hill, 1998, pp.172.
• "Neuro-ophthalmology." In Cecil Textbook of Medicine, edited by J. Claude Bennett and Fred Plum. Philadelphia, PA: W. B. Saunders, 1996, pp. 2019-20.

  Organizations

• American Academy of Ophthalmology. P.O. Box 7242, San Francisco CA. 94140-7424. (415) 561-8500. http://www.eyenet.org.
• American Optometric Association. 243 North Lindbergh Blvd., St. Louis, MO 63141. (314) 991-4100. http://www.aoanet.org.

Gale Encyclopedia of Medicine. Gale Research, 1999.