Astigmatism

Astigmatism, pronounced uh STIHG muh tihz uhm, is a visual defect in which both nearby and distant objects appear blurred. The defect is usually found in both eyes. In most cases, astigmatism is caused by the shape of the cornea.

A normal cornea has a spherical shape, somewhat like a basketball cut in half. As light rays pass through a normal cornea, they are bent so they focus at a single point on the retina. In people with astigmatism, the cornea is shaped somewhat like a football cut in half lengthwise. The length and the width of the football-shaped cornea have unequal curvatures (degrees of curve), and the difference between these curves determines how much astigmatism the person has. Light rays entering an eye with astigmatism cannot focus on a single point on the retina. Instead, the rays meet at two points, one or neither of which is on the retina.

Many cases of astigmatism are present at birth. Some cases result from injury or disease. Astigmatism may develop or change as a person grows older, and it is often associated with nearsightedness or farsightedness. Mild cases of astigmatism may come and go.

Symptoms of astigmatism include blurred vision, double vision in one eye, eyestrain, fatigue, and headaches. People with astigmatism may squint in an effort to see clearly. Doctors treat the defect by prescribing glasses or contact lenses. In some cases, surgical or laser treatment of the cornea may restore a more spherical shape and reduce or eliminate astigmatism.

Contributor: Ronald A. Krefman, O.D., Optometrist.

Astigmatism

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