MEDICINE / SMOKING : Two Studies Link Cigarettes to Cataracts

People who smoke cigarettes face up to twice the risk nonsmokers have of developing cataracts, according to two separate studies by researchers at Harvard Medical School and Brigham and Women’s Hospital in Boston.

The findings, which confirm earlier suggestions of a link, indicate that about 20% of the cataract cases in the United States may be attributed to smoking.

One study of more than 50,000 female nurses found a 60% increased risk of cataracts in smokers compared to nonsmokers. A study of 17,800 male physicians found that current smokers had twice the risk of developing cataracts compared to people who had never smoked. The results of both studies, which are based on large, continuing epidemiology research projects, are being published today in the Journal of the American Medical Assn.

Smoking cigarettes “will make you lose your vision at a more rapid rate,” said Dr. Charles H. Hennekens, a professor at Harvard Medical School and one of the authors of the report using data from the Physicians’ Health Study.

“The important point is that the findings are very similar,” said Susan E. Hankinson, the principal author of the report based on data from the Nurses’ Health Study. “These two studies provide substantial additional evidence that cigarette smoking is an independent, important and avoidable risk factor for cataracts,” she said.

Cataracts are the world’s leading cause of blindness. They develop when the lens in the eye becomes clouded. Eventually, the blockage of light can become so disabling that it requires surgery, which usually corrects the problem.

In the United States, statistics indicate that cataracts are responsible for more than 3.3 million cases of vision impairment, mostly in the elderly. Each year there are more than 1.1 million surgeries to extract cataracts.

Hankinson said it is not clear how cigarette smoke might cause cataracts. The leading hypothesis is that the smoke triggers biochemical changes in the lens that interfere with its ability to transmit light.

It is also not known whether the effects on the lens are related to cigarette smoke in the air or smoke products in the bloodstream. Nor is it known whether nonsmokers are put at a higher risk by being exposed to large amounts of cigarette smoke.

A handful of studies have examined possible links between cigarette smoking and cataracts, but the findings have been inconsistent. The new studies are far larger.

Unlike previous research, the study gathered information on smoking and other possible risk factors before any of the participants developed cataracts. This makes the findings more persuasive than studies in which people are asked about possible risk factors after they have cataracts.

Both studies suggest that former cigarette smokers are also at an increased risk of cataracts compared to people who have never smoked. But researchers cautioned that this conclusion was more tentative and required confirmation.