Soft contacts: extended wear poses hazard.
People who wear soft contact lenses while they asleep face an increased risk of ulcerative keratitis, an eye infection that can lead to permanent vision loss, according to a pair of scientific reports. The risk appears to mount with each consecutive day of uninterrupted contact wear.
In a study involving 557 people, Oliver D. Schein of the Harvard-affiliated Massachusetts Eye and Ear Infirmary in Boston found that people who used extended-wear contact lenses overnight ran a risk of ulcerative keratitis 10 to 15 times greater than people who used the daily-wear type of lens during the day only.
According to the Food and Drug Administration, 4.1 million people in the United States use extended-wear soft contacts and another 9.1 million use daily-wear soft contacts. Schein and his colleagues found that 11 percent of the daily-wear users disregarded FDA guidelines to remove such contacts nightly. Compared with people who used the same contacts correctly, these users ran nine times the risk of ulcerative keratitis.
People practicing poor lens hygiene showed an increased risk of the eye infection, but frequent cleaning alone did not remove the risk of getting ulcerative keratitis. Even people with good hygiene habits who wore lenses overnight faced a threat of ulcerative keratitis, the researchers found.
Scientists speculate that contacts cause ulcerative keratitis by cutting off the oxygen supply to epithelial cells on the eye surface. When the cells die, they form an ulcer that can become infected if bacteria or other microorganisms gain a foothold. Doctors treat ulcerative keratitis with eyedrop antibiotics, but even successful treatment can leave patients with vision loss if scar tissue forms in front of the pupil, Schein says.
In a second report -- a survey of 4,178 New England households and of all practicing ophthalmologists in the study area -- Schein, Eugene C. Poggio of Abt Associates in Cambridge, Mass., and their colleagues estimate that one of every 500 extended-wear users each year develops ulcerative keratitis. Their risk estimate for daily-wear users is less: About one of every 2,500 users each year will develop the infection. Both reports appear in the Sept. 21 NEW ENGLAND JOURNAL OF MEDICINE.
Last May, after reviewing prepublication data from both studies, FDA officials asked manufacturers of soft contact lenses to revise their labeling instructions, advising consumers to remove extended-wear lenses for cleaning after seven days of continuous use.
Prior to the May announcement, FDA labeling instructions allowed people to keep such lenses in place for up to 30 days, a practice that "presents too high a risk" of ulcerative keratitis, according to an FDA statement issued in May. "The [Boston] data did not identify a wearing time that will eliminate the risk altogether, but seven days represents a relatively short, easy-to-remember interval which will encourage users to remove their lenses and clean them," FDA says.
Some eye specialists believe FDA should tighten its recommendation further. "It's not at all clear to me why seven days became a magic number," says Alfred Sommer, an ophthalmologist at the Wilmer Institute of Johns Hopkins Hospital in Baltimore. "It's six days too long." Sommer says people should wear contacts overnight only rarely. Ophthalmologist Ronald E. Smith of the University of Southern California in Los Angeles agrees. In an editorial accompanying the two research reports, Smith writes: "Since wearing a soft contact lens continuously for even a week substantially increases the risk of ulcerative keratitis, and since patients are likely to push beyond any suggested guidelines, there is concern that this change does not go far enough in warning the patients of the risk."
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|Date:||Sep 23, 1989|
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