Astigmatism (a-STIG-ma-tiz-um) is an eye condition that causes objects to appear blurry because the front part of the eye is misshapen.
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The eyeball usually is round and nearly the same size as a ping-pong ball. The front part contains a clear layer of tissue called the cornea and the lens that help to focus the light that enters the eye. When people have astigmatism, the cornea and/or the lens is misshapen and their curved surfaces are unequal. If the curve is only slightly off shape, then only objects at a distance might appear blurry. People with more serious astigmatism, however, may see the world as if they were looking in a funhouse mirror that distorts all images.
Who Gets Astigmatism?
Astigmatism is a common problem. Many people may have slight variations in the shape of their cornea or lens that do not cause problems with their eyesight. In others, however, these structures are shaped in ways that distort the light that enters the eye. The cornea usually is smooth and rounded, like the surface of a ping-pong ball that is cut in half. A person with astigmatism, however, might have a cornea that is curved more like the top of a football, as if the ping-pong ball were pulled out from its edges. Or the cornea may have peaks and valleys on its surface, instead of a smooth, rounded covering, and that too will distort vision.
No one is sure what causes astigmatism. It usually is present at birth and often is found in several members of the same family. This means that in some cases the trait is inherited, like hair color and eye color.
What Happens to Vision When People
These variations in the shape of the cornea or lens cause the images a person with astigmatism sees to be out of focus when they reach the retina. The retina is made of layers of light-sensitive cells at the back of the eyeball that act like the film in a camera. The distorted image is projected onto the retina and transmitted to the brain for processing through the optic nerve.
The first signs of astigmatism depend on how severely the cornea or lens is misshapen. If it is only a mild problem, people with astigmatism may find that they have headaches or tired eyes at times, or distorted vision at certain distances. Those with more severe astigmatism may find they have blurry vision that makes reading, playing sports, and other activities difficult. Often, the problem is found during an eye exam in school, at the doctor's office during a check-up, or when a parent notices that a child is having trouble seeing well.
What Is the Treatment for Astigmatism?
Astigmatism is managed with prescription eyeglasses or contact lenses. These help change the way that images are focused as they pass through the cornea and the lens. With eyeglasses, images can appear clear and undistorted when they reach the retina. Usually, astigmatism does not get worse as people get older.
Cassel, Gary H., M.D., Michael D. Billig, O.D., and Harry G. Randall, M.D. The Eye Book: A Complete Guide to Eye Disorders and Health. Baltimore: Johns Hopkins University Press, 1998. A good general reference on eye problems.
The U.S. National Eye Institute posts a resource list of eye
health-related publications and organizations at its website.