Contacts: disposables still pose eye risk.
Associated most frequently in a number of studies with soft contact lenses -- especially extended-wear varieties, which can be worn overnight -- this corneal disease can result in permanent loss of vision.
One of the new studies focused on 42 individuals diagnosed with ulcerative keratitis by two Michigan ophthalmologists, John F. Stamler and David D. Verdier of Grand Rapids. Together with Oliver D. Schein of Johns Hopkins Hospital's Wilmer Eye Institute in Baltimore and his co-workers, the Michigan doctors compared each keratitis sufferer with five other contact-lens wearers who had been prescribed their lenses--of any type--by the same practitioner at the same time.
They found "that the disposable lenses posed an ulcerative keratitis risk 14 times higher than daily wear [of nondisposable soft contacts]," according to
Patricia Owens Buehler, who led the study. That wasn't surprising, because a 1989 study that Schein directed found a similar risk for extended-wear, nondisposable soft contacts (SN: 9/23/89, p.197), says Buehler, now at the Oregon Health Sciences Center in Portland.
The seven-fold higher risk of keratitis associated with disposable versus nondisposable extended-wear soft contacts "was unexpected," she says.
This and a related study appear in the November ARCHIVES OF OPHTHALMOLOGY. That second study compared rates of eye problems in 323 contact-lens wearers entering Moorfields Eye Hospital in London over three months. Unexpectedly, its authors note, "extended- and daily-wear disposable lenses were associated with higher risks of keratitis than other lens types, including conventional extended-wear lenses."
Buehler's team is now sifting through data on wearing schedules and hygiene practices from its study trying to explain why more disposable wearers developed keratitis. She believes overnight wear will explain most of the disposables' risk. "We know that wearing [soft] lenses overnight, as most people do with disposables, increases your risk of this disease," she notes. And she says that while virtually all disposable wearers leave their lenses in overnight, only 50 percent of people with soft extended-wear lenses do.
"The problem with wearing soft lenses overnight -- disposable or not -- is that none allows the full amount of oxygen to reach the cornea and keep it from swelling," notes Houston ophthalmologist James E. Key II. At the American Academy of Ophthalmology's annual meeting in Dallas last week, he reported that no soft lens yet allows sufficient oxygen to reach the eye when lids are shut during sleep. Only rigid, gas-permeable lenses, which aren't nearly as comfortable to sleep with, let in enough air, he says.
With the exception of keratitis, disposables pose less risk of eye problems than other soft lenses, several studies show. And even for patients wearing soft lenses overnight, the absolute risk of keratitis remains less than 1 percent, says Peter C. Donshik, a West Hartford, Conn., physician and president of the Contact Lens Association of Ophthalmologists.
The two main points, Donshik emphasizes, are to disinfect any lens that will be reused -- even a disposable -- and for contact-lens wearers to call an ophthalmologist immediately if they develop the red, painful, or blurry eyes that may signal keratitis.
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|Title Annotation:||disposable contact lenses may cause eye inflammation|
|Date:||Nov 21, 1992|
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