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
The hospital patients answered a questionnaire and the control patients in
the general population were interviewed by telephone from late 2003 to
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
''Gas-permeable lenses are safer than any other type of lenses,'' Dart says,
although he adds that they are not a popular choice among contact lens wearers,
who tend to find them uncomfortable.
Even though the daily disposable wearers had more risk of infection than
those who wore reusable soft lenses, vision loss from the infection was less
likely to occur in the daily disposable lens wearers. None of the daily
disposable lens wearers lost vision beyond 20/40, he says.
"It's safer to use a daily disposable [than a reusable]," Dart says,
"because the type of bugs you get are less nasty." Reusable lenses must
be disinfected and stored, and "lens cases harbor nasty bacteria in some
patients," he says.
Some brands were associated with more infections than others, Dart found,
but he says most of the contact lenses he studied have probably been redesigned
since the study was done.