Newer Contact Lenses Don't Cut Infections
Daily Disposables, Newer Materials Have Not Reduced Infection; Overnight Wear Increases Risk Most, Studies Show
Oct. 3, 2008 -- Neither the newer contact lenses that allow more oxygen into the eye nor daily disposable lenses have reduced the risk of a dangerous eye infection as hoped, according to two new studies.
Whatever the type of lens, sleeping with them in is the biggest risk factor for a painful infection of the cornea called microbial keratitis, the researchers also find.
"If you wear any of these lenses overnight, you have five times the risk of infection," says John Dart, DM, a consultant ophthalmologist at Moorfields Eye Hospital in London. He is the lead author of one study and co-author of the other.
"These are the first well-designed studies to look at daily disposables and the newer silicone hydrogel lenses," Dart tells WebMD. The silicone hydrogel lenses were introduced in 1999 in the hope that by improving oxygen transmission to the cornea, which has no blood supply of its own, it would decrease infection risk, he says. Daily disposables, introduced in 1999, were also thought to be protective against infection because they're not exposed to lens cases, which can be contaminated.
But neither of the studies, published in the October issue of Ophthalmology, found that to be true, Dart says.
However, Dart says, it's important to put the risk in perspective. "The risk of getting microbial keratitis is actually overall not large," he says. It affects about 1 in 2,000 contact lens wearers. But it can cause vision loss, sometimes permanently.
Contact Lenses & Infection Risk: The U.K. Study
In the study led by Dart, the researchers evaluated 367 contact lens wearers with microbial keratitis, 1,069 hospital patients who wore contact lenses but had no contact lens-related disorders, and 639 contact lens wearers in the general population.
The hospital patients answered a questionnaire and the control patients in the general population were interviewed by telephone from late 2003 to 2005.
Daily disposable wearers had 1.5 times higher risk of microbial keratitis than those who wore soft lenses that were replaced every one to four weeks, and those who wore rigid gas-permeable lenses had the least risk of infection.