Newer Contact Lenses Don't Cut Infections

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.

''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.

Contact Lenses & Infection Risk: The Australian Study

In the second study, a team led by Fiona Stapleton, PhD, of the University
of New South Wales, interviewed 285 contact lens wearers who had microbial
keratitis and 1,798 lens wearers without the infection.

After looking at the type of lenses worn, wearing patterns, and other
factors, they estimated the annual incidence for the infection.

They also found that new lens materials haven't reduced infection. Overnight
use was the strongest risk factor for infection, just as in the U.K. study.

For instance, they estimate that microbial keratitis occurred in 1.2 per
10,000 of those who wore daily-wear rigid gas-permeable lenses but in 25.4 per
10,000 of those who wore silicone hydrogel lenses overnight.

Other factors that increased the risk of ifection included smoking, buying
lenses over the Internet, wearing lenses beyond the recommended time spans, and
improper hand cleaning before handling lenses.

Contact Lenses & Infection: Study Interpretations

Finding that the newer lens materials don't reduce infection risk is
disappointing, Dart writes.

Although experts thought that the lack of oxygen getting to the cornea was a
factor in infections, the findings suggest that other factors may be more
important, he says.

The lenses may reduce the turnover of skin cells on the front of the eye,
for instance, Dart says, boosting infection risk.

The studies were funded from a variety of sources, including CIBA Vision
USA, which makes a variety of contact lenses. One of the supporting
organizations, The Vision Cooperative Research Center, receives a royalty on
the sale of silicone hydrogel lenses.

Contact Lenses & Infection: Second Opinion

The findings about the risk of overnight wear come as no surprise to Thomas
Steinemann, MD, a spokesman for the American Academy of Ophthalmology and
professor of ophthalmology at Case Western Reserve University
in Cleveland.

"That confirms what we have always known for years," he says.
"Sleeping in your lenses is not a good thing, even if they are continuous
wear. It is a risk factor, probably the risk factor, for microbial
keratitis-associated vision loss."

"Don't sleep in your contact lenses, ever," he says. "That
includes taking naps in them."

Also important, he says, is to pay attention to lens hygiene. "Follow
your eye care professional's and manufacturer's advice about cleaning," he
says.

By Kathleen Doheny
Reviewed by Louise Chang
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