Lifting the Clouds of Cataracts

by Food and Drug Administration (FDA)

You're approaching retirement, feeling healthy and looking forward to many more active and productive years. But then your vision begins to grow cloudy. Everything you look at has a yellowish tint. Simple tasks like reading or driving a car become difficult. Street signs and faces aren't as sharp as they once were. Bright sun and auto headlights hurt your eyes. New eyeglass prescriptions improve vision for a while — but eventually they no longer help.

The culprit is cataracts, a condition that will beset most people if they live long enough. This disorder affects 60 percent of people older than 60 and occurs when the normally clear, aspirin-sized lens of the eye starts to become cloudy, impairing vision.

Experts estimate that 1.2 million Americans will be diagnosed in 1989 with cataracts that require treatment, compared with 123,000 in 1978. Most of the increase is due to the growing numbers of elderly in the United States, many of whom want to continue driving cars, reading and traveling — activities for which clear sight is vital.

Until recently, anyone who developed cataracts and needed surgery faced a procedure that involved pain and often less than satisfactory results. Until the late 1970s, doctors removed the cloudy lens in a surgical procedure that required a hospital stay of five to seven days. Afterward, the patient had to wear thick "Coke bottle" glasses or contact lenses — neither of which could completely restore vision to its previous level.

Today, there's little need for such complicated treatment. Advances in medicine have made cataracts much less worrisome. Now, the clouded lens is surgically removed and replaced with a plastic intraocular lens (IOL) in an hour-long operation that often requires no hospitalization.

"The intraocular lens has revolutionized the treatment of cataracts," says Carl Kupfer, M.D., director of the National Eye Institute in Bethesda, Md. "Implantation of the lens is one of the most successful operations in medicine."

How a Cataract Forms

A cataract forms in the eye's lens, the transparent structure behind the iris (the colored membrane surrounding the pupil). The lens focuses light on the retina, the light-sensitive membrane at the back of the eye which converts light impulses into nerve signals to produce clear visual images. Clouding of the lens — much like smearing grease over the lens of a camera — can develop at any age but most often appears in people older than 42.

Most cataracts are caused by a change in the chemical composition of the lens. In a small percentage of cases, the chemical changes are caused by a hereditary enzyme defect, trauma to the eye, diabetes, or use of certain drugs, such as the steroid prednisone.

Precisely why cataracts occur with age is unknown, but ultraviolet radiation, particularly from the sun, is thought to play a major role in creating the chemical change in the lens responsible for most cataracts. Experimental evidence suggests that UV radiation can cloud the lens by forming highly reactive chemical fragments called "free radicals." These, in turn, disrupt the delicate structure of the lens. The type of ultraviolet radiation from the sun called UVB — the kind that causes blistering sunburn and skin cancer — is thought to be a major factor because the lens absorbs these rays.

Indeed, in a recent study of 838 Chesapeake Bay professional fishermen, Hugh Taylor, M.D., of Johns Hopkins Hospital in Baltimore, Md., found a strong association between ultraviolet radiation and cataract formation. Fishermen with the highest levels of ultraviolet radiation exposure had three times the risk of contracting cataracts compared with those with the least exposure. Those with cataracts had 20 percent more exposure to sunlight in every year of life. Taylor's studies suggest that cataracts can be prevented by avoiding sun exposure between 10 a.m. and 4 p.m., when sunlight is strongest, and by wearing a wide-brimmed hat and sunglasses.

A cataract can develop so slowly that a person may not even know it's there. If the cataract is on the outer edge of the lens, no change in vision may be noticeable. Cloudiness near the center of the lens, however, usually interferes with clear sight.

Symptoms

Symptoms of developing cataracts include double or blurred vision, sensitivity to light and glare (which may make driving difficult), less vivid perception of color, and frequent changes in eyeglass prescriptions. As the cataract grows worse, stronger glasses no longer improve sight, although holding objects nearer to the eye may help reading and close-up work. The pupil, which normally appears black, may undergo noticeable color changes and appear to be yellowish or white, says Peter Hersh, M.D., an assistant surgeon at Boston's Massachusetts Eye and Ear Infirmary.

Cataracts are typically detected through a medical eye examination. The usual test for visual acuity, the letter eye chart, may not, however, reflect the true nature of visual loss, says the American Academy of Ophthalmology. Other tests — which measure glare sensitivity, contrast sensitivity, night vision, color vision, and side or central vision — help nail down the diagnosis.

Because most cataracts associated with aging develop slowly, many patients may not notice their visual loss until it has become severe. Some cataracts remain small and never need treatment; others grow more quickly and progressively larger. Only when a cataract seriously interferes with normal activities is it time to consider surgery, doctors say. People who depend on their eyes for work, play and other activities may want their cataracts removed earlier than those whose needs are less demanding.

Some experts estimate that about 88 of every 100 persons receiving IOLs will achieve 20/40 vision or better. (An individual with 20/40 vision can read letters on an eye chart from 20 feet away, while a person with normal 20/20 vision can read the chart from 40 feet away; 20/40 vision is good enough to get a driver's license in most states.) Among those who do not have other eye diseases, about 94 of 100 will achieve 20/40 vision.

About the Author

www.fda.gov
FDA is A United States government body that oversees medical devices, including contact lenses, intraocular lenses, excimer lasers and eyedrops. In the US, these products must be approved by the FDA before they can be marketed.