August 26, 1998
Exposure to sunlight increases risk of getting cataracts, according to a Johns Hopkins study.
"We've found there is no safe dose of exposure to the sun's ultraviolet B rays when it comes the risk of cortical cataract, which means people of all ages, races and both sexes should protect their eyes from sunlight year-round, says Sheila West, Ph.D., professor of ophthalmology at the Johns Hopkins Wilmer Eye Institute.
Cataract, a clouding of the eyes' clear lenses, occurs when proteins in the lens change their structure due to UV-B light exposure and block light coming into the eye. Cortical cataracts affect the front of the lens.
West is senior author of a report on the study, published in the August 26 issue of Journal of the American Medical Association. The study was supported by the National Institute on Aging.
The finding comes several years after the so-called "watermen's study," in which West and her colleagues showed that crab fisherman working on Maryland's Chesapeake Bay had more cortical cataract compared to people with less sunlight exposure. The current finding shows that even the general public -- those who work indoors and only get sunlight during leisure activities in the yard or on vacation -- may be at increased risk for cortical cataract if precautions aren't taken.
The Hopkins study, conducted in Salisbury, Md., determined the amount of UV-B exposure in 2,520 adults, age 64 to 84, of whom 26.4 percent were African Americans. The Hopkins researchers photographed the lenses of all participants and questioned them about their use of glasses, sunglasses and hats during work and leisure activity, as well as the geographic locations of these activities.
The team also used a special device mounted on eyeglasses of over 250 participants to measure the amount of UV-B light reaching their eyes. Then, using a "correction factor" model developed by the National Aeronautics and Space Administration, the researchers estimated exposure to UV-B the participants got when they traveled to areas outside the Eastern Shore.
The results of the study are especially important for children, according to West, because they have many years of exposure ahead of them, and the effect of sunlight exposure appears to be lifelong. "Kids get sunburned just like adults," West says. "So there's no reason to think they are more resistant than adults to lens damage from UV-B rays."
"Every time you go out into the sun, your eyes can take a hit from UV-B rays," says West. "The good news is it's never too late to start protecting your eyes, because the lens change is probably from an accumulated dose over the years. That's why everyone needs to get into the habit of protecting their eyes."
Even inexpensive, plastic sunglasses are good absorbers of UV-B, according to West, and how dark the glasses are isn't an issue, since any plastic eyewear will absorb the invisible UV-B light. For children, however, the glasses should be shatterproof to prevent eye injury in case of an accident. Dark glasses are needed to block the visible light from the sun.
The researchers calculated there is a 10 percent increase in risk for cataract for every 0.01 "Maryland sun years" of exposure. A Maryland sun-year is the amount of UV-B that falls in Maryland over one year. The eye receives anywhere from 9 percent to 18 percent of this exposure.
Other authors of the study include Donald D. Duncan, Beatriz Munoz, Gary S. Rubin, Linda P. Fried, Karen Bandeen-Roche, and Oliver D. Schein.