Amblyopia

Amblyopia is the name for diminished vision in one or both eyes, usually without any obvious defect. Amblyopia is not the same as nearsightedness, farsightedness, or astigmatism. (These conditions can be corrected with eyeglasses or contact lenses.)

There are two main types of amblyopia: lazy-eye amblyopia and toxic amblyopia.

Lazy-Eye Amblyopia

Lazy-eye amblyopia occurs frequently in young children whose eyes do not line up correctly (a condition known as strabismus). To prevent double vision (in which the patient sees two images instead of one), the brain suppresses the sight of one eye; the other eye does all the work. Without treatment, the brain structures dependent on the eye that is not working may atrophy (waste away) or fail to develop.

There are usually no obvious symptoms of this form of amblyopia. By the time the condition is recognized, the eye may be permanently damaged. Usually, the child appears to see as well as the next child. Sometimes, however, the condition that causes the amblyopia is very noticeable: The eyes may turn either inward or outward, or one eye may be looking up while the other is looking down.

To fully restore sight in the lazy eye, treatment must begin before the child is four to six years of age. If the eyes are out of focus because some of the muscles of the lazy eye are weaker than others, the condition may be corrected by wearing special glasses or contact lenses, by doing eye exercises, by patching the good eye and prescribing corrective lenses for the amblyopic eye (thereby forcing the lazy eye to work), or by surgery. Periodic reexaminations are needed until the child is at least ten years of age.

If the eyes of a baby are continually out of alignment in the first weeks of life or are still out of alignment from time to time at six months of age, the condition should be investigated. A simple eye test given in the doctor's office should show whether one eye is not working properly. Evaluation should not be delayed. A child will not "grow out" of either strabismus or amblyopia.

Toxic Amblyopia

Toxic amblyopia, which usually occurs in both eyes, can result from excessive drinking of alcoholic beverages over a long period of time. (This may be due mainly to the poor nutrition of heavy drinkers, who get most of their calories from alcohol.) It may also be found in heavy cigarette smokers and in people exposed to various chemicals and drugs, including lead, methanol (wood alcohol), digitalis, chloramphenicol, and arsenic.

The toxic substance causes swelling and irritation of the optic nerve around the site at the rear of the eye where the nerve leaves the eyeball. If the irritation continues, it can cause lasting damage to the nerve, sometimes resulting in total blindness.

Symptoms include pain on moving the eyeball and an increasing area of poor eyesight in or near the center of the field of vision.

Treatment is to stop exposure to the poison, if it can be discovered. In the case of lead poisoning, the patient is given medicine that combines with the lead and draws it out of the body tissues (this treatment is known as chelation therapy). If the cause is removed at once, vision may improve -- unless there has been permanent damage to the optic nerve.