Studies smoke out the risk of cataracts.

Cigarette smoke may do more than temporarily cloud your vision. Two studies confirm that smoking boosts a person's risk of developing cataracts, an opacity in the lens of the eye. Both studies associate smoking with a particularly serious form of cataract for the first time.

The new data suggest that smoking causes 20 percent of all U.S. cataract cases, asserts Sheila West of Johns Hopkins Hospital in Baltimore. "It appears that the litany of ills associated with smoking is growing, as we add to it cataracts, the world's leading cause of blindness," she writes in an editorial accompanying the two research reports in the Aug. 26 JOURNAL OF THE AMERICAN MEDICAL ASSOCIATION.

The two studies provide the strongest link yet between smoking and cataracts, says epidemiologist William G. Christen of the Harvard Medical School in Boston, who led one of the investigations. He and his colleagues used data culled from the Physicians' Health Study, a trial involving male physicians that began in 1982. The 17,824 men studied by Christen's group showed no sign of cataracts at the outset of the study, he says.

Over the next five years, the team monitored the volunteers, identifying 557 cases of cataracts. Statistical analyses revealed that men who reported smoking at least a pack (20 cigarettes) per day at the study's start ran a significantly greater risk of cataracts than did men who had never smoked. Smokers faced an estimated 200 percent increased risk of developing a posterior subcapsular cataract--a visually disabling condition that strikes the back of the lens -- and an estimated 100 percent increased risk of nuclear sclerosis cataract, a less serious form in which the opacity occurs in the center of the lens. This is the first time scientists have demonstrated an association between smoking and posterior subcapsular cataracts, which are more likely to require surgery, Christen says.

People with cataracts often experience progressive blurring of their vision as the normally clear lens becomes increasingly opaque. Surgical removal of the cloudy lens, followed by implantation of an artificial lens, restores vision in most cases, Christen says.

The cigarette-cataract connection seems to extend to women as well as men. In a separate report, Susan E. Hankinson, also at the Harvard Medical School, and her colleagues describe a study of more than 50,800 women who participated in the Nurses' Health Study, a trial of registered nurses that began in 1976.

After monitoring the women for eight years, the researchers identified 493 cases of cataracts. Their statistical analyses showed that, compared with non-smokers, women smoking at least 30 cigarettes per day during the study had about a 60 percent greater risk of developing cataracts serious enough to require surgery. The study also linked smoking with posterior subcapsular cataracts.

For ex-smokers, the risk lingers long after quitting. Hankinson's team discovered that women who had once been moderate to heavy smokers continued to face a significantly higher risk of cataracts than nonsmokers.

Researchers have yet to pinpoint the mechanism by which smoking encourages cataract formation. However, Hankinson notes that many smokers have low blood levels of antioxidants, substances that protect cells from the damaging effects of molecules known as free radicals. Compared with nonsmokers, smokers may thus sustain greater free-radical damage to the lens.