Nearsightedness

Nearsightedness, also called myopia, is a visual defect that causes blurred distance vision. Except in extreme cases, near vision remains clear. For the eye to form a clear image, the light rays reflected or given off by an object must come together on the retina, the light-sensitive tissue lining the back and sides of the eyeball. In most nearsighted people, the eyeball is longer than normal from front to back. As a result, light rays from a distant object meet in front of the retina. When the rays do strike the retina, they form a blurred image.

Studies have shown that people inherit a tendency to develop nearsightedness. But intense close-up visual activity may contribute to the development of the condition. Some babies develop nearsightedness by age 1, but the problem corrects itself as the eyes grow. Research indicates these individuals usually develop the defect again during or after adolescence.

Nearsighted people can wear concave glasses or contact lenses to clear up their distance vision. Concave lenses are thinner in the middle than at the edges. They bend light rays outward so that the rays meet on the retina. See Eye.

A surgical procedure called radial keratotomy can correct nearsightedness. This procedure, developed in the mid-1970's, flattens the cornea (clear tissue covering the eyeball) so that light rays passing through it meet on the retina. Laser surgery also can reshape the cornea and correct nearsightedness. However, the long-term results of these surgical procedures are unknown.

Contributor: David E. Eifrig, M.D., Chairman, Department of Ophthalmology, Univ. of North Carolina.

Nearsightedness

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