A cataract is a cloudiness in the lens of the eye, which is normally clear and transparent. The cloudiness caused by a cataract may eventually lead to decreased vision and blindness.
The lens is positioned near the front of the eyeball. It is protected by the cornea, which covers the front of the eyeball. The purpose of the lens is to focus the light waves that enter the eye. Muscles around the lens can change the shape of the lens. In this way, objects both close at hand and far away can be brought into focus.
The lens is made up of about 35 percent protein and 65 percent water. Proteins are chemical compounds found in all cells. As people grow older, the chemicals present in their eyes may change. Proteins may break down, water may seep out of the eye, or other changes may occur. One consequence of such changes is the formation of cataracts.
Cataracts are common in older people. They are so common that they are regarded as a normal part of the aging process. For those between the ages of 50 and 65, the chance of having a cataract is about 50 percent. Beyond the age of 70, the risk rises to about 70 percent.
Cataracts also occur in young people, but are much less common. For example, the lens may be injured by some foreign object, which may lead to the formation of a cataract. Cataracts are also caused by certain diseases, such as diabetes mellitus (see diabetes mellitus entry).
Cataracts generally have little or no effect on vision in their early stages. As they develop, they can lead to vision problems and, eventually, blindness may result.
The vast majority of cataracts are thought to have no specific cause. They simply develop as a person grows older. Researchers are exploring a number of theories about possible causes of cataracts. These theories suggest that smoking, alcohol, and high-fat diets may increase a person's risk for cataracts. They also suggest that vitamin supplements may decrease the risk for cataracts.
The most common symptom of cataracts is a gradual, painless change in one's vision. Objects become more blurry, filmy, or fuzzy to a person with cataracts. Some other common symptoms of cataracts include the following:
Cataracts are easily diagnosed by any eye specialist. They can often be detected before a patient is aware of vision problems. The most direct diagnosis is made by shining a light into the patient's eyes. Color changes or cloudiness are often visible if a cataract is developing.
No treatment is needed for mild cases of cataracts. If they do not interfere with a patient's vision, they are not treated. If moderate vision problems develop, a stronger eyeglass prescription may be all that is needed.
In more serious cataract cases, surgery may be necessary. Surgery is the only procedure available for treating advanced cases of cataracts. Cataract surgery is relatively simple. By the late 1990s, it was the most frequently performed surgery in the United States.
Cataract surgery can be performed in a doctor's office and usually lasts about an hour. The cloudy lens is removed. An artificial plastic lens is then inserted into the space formerly occupied by the damaged lens. The patient is given antibiotics and steroids after the surgery. The antibiotics protect against infection by bacteria. The steroids help reduce the pain and inflammation caused by the surgery.
Many cases of cataracts never require treatment other than a change in one's eyeglass prescription. If surgery is required, the success rate is very high. More than 90 percent of patients experience improved vision. Complications occur in a very small fraction (3 to 5 percent) of cataract surgeries. These complications include infections, swelling of the cornea, bleeding, and damage to the retina.
Since most cases of cataracts are part of the natural aging process, there is not much that can be done to prevent their development. Wearing dark glasses in direct sunlight may be helpful. Radiation from the sun is thought to be one possible cause of changes in proteins in the lens. A healthy diet rich in citrus fruits, sweet potatoes, carrots, and green leafy vegetables, and supplemented by vitamins, may also be helpful in delaying the onset of cataracts.
Salmans, Sandra. Your Eyes: Questions You Have … Answers You Need. Allentown: People's Medical Society, 1996.
Shulman, Julius. Cataracts—from Diagnosis to Recovery: The Complete Guide for Patients and Families. New York: St. Martin's Press, 1995.
American Academy of Ophthalmology (National Eyecare Project). PO Box 7424, San Francisco, CA 94120–7424. (800) 222–EYES. http://www.eyenet.org.
American Optometric Association. 243 North Lindbergh Boulevard, St. Louis, MO, 63141. (314) 991–4100. http://www.aoanet.org.
Lighthouse International. 111 East 59th Street, New York, NY 10022. (800) 829–0500. http://www.lighthouse.org.
Prevent Blindness America. 500 East Remington Road, Schaumburg, IL 60173. (800) 331–2020. http://www.prevent-blindness.org.