Regular exposure to heavy doses of sunlight makes a person three times as likely to develop cataracts, a study of Chesapeake Bay watermen showed. Cataracts are a clouding of the lens of the eye, and among older people they can progress from a light fogging to blindness. About 20 million people in the world are blinded by cataracts, and more than a million people a year in the United States have operations to remove them. But the study by the Wilmer Eye Institute at Johns Hopkins Medical Institutions showed that protective measures can cut down on the development of cataracts. It has long been suspected that heavy exposure to sunlight could cause cataracts, but the Johns Hopkins study, reported in the New England Journal of Medicine, offers the first conclusive evidence.