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New Contacts, Old Infections. Warning for extended wear contacts!
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acemanvx@yahoo.com
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Joined: 15 Nov 2005
Posts: 732

PostPosted: Fri Jul 21, 2006 7:44 am    Post subject: New Contacts, Old Infections. Warning for extended wear contacts! Reply with quote

The newest extended-wear contact lenses have a similar risk of eye
infections as older soft lenses worn for fewer nights.

That news is reported in Ophthalmology. It comes from postmarketing
studies funded by CIBA Vision, which makes the silicone hydrogel
lenses, marketed as Night & Day.

The researchers included Oliver Schein, MD, MPH, of Johns Hopkins
University's medical school.

Lenses' History

The FDA approved the silicone hydrogel lenses in 2001 for continuous
wear for up to 30 nights.

Older generations of extended-wear contacts had been associated with
rare cases of vision loss and eye infections. That prompted the FDA's
1989 decision to cut extended wear to seven days.

Years later, silicone hydrogel lenses were developed. Compared with
older lenses, they allow four times as much oxygen to reach the eye.
Better oxygen flow was seen as a way to possibly lower infection risk
in the eye's cornea.

The FDA ordered postmarketing studies of silicone hydrogel lenses to
check corneal infection rates.

Year-Long Study

The study included 6,245 people who had been given prescriptions for
the silicone hydrogel lenses. Most (80%) wore their lenses nonstop for
at least three weeks.

During the year-long study, few participants had corneal infections.
Two had corneal infections that led to vision loss. Eight others had
corneal infections that didn't cause vision loss.

Overall, the yearly rate of corneal infections was 18 per 10,000
people, the study shows.

That's similar to rates previously reported for conventional,
extended-wear soft lenses worn for fewer consecutive nights, according
to the researchers.

Researchers' Pecking Order

Schein's team calls contact lenses "very safe" in general, though
they note that contact lenses are associated with some extra risks,
compared with eyeglasses.

They rank the risk of vision loss from eye infection for different
types of contact lenses:


Lowest risk: Rigid, gas-permeable contact lenses for daily wear


Next-to-lowest risk: Soft contact lenses for daily wear


Highest risk: Silicone hydrogel contact lenses for extended wear of
three-to-four weeks

However, they're not calling silicone hydrogel lenses dangerous. The
odds appear "reasonable," write the researchers, for people who
understand the risks and want to wear their contacts around the clock.

The study notes that one researcher is a CIBA Vision consultant and one
is a CIBA Vision employee.

SOURCES: Schein, O. Ophthalmology, Dec. 2005; vol 112: pp 2172-2179.
News release, Johns Hopkins University.


By Miranda Hitti
Reviewed by Louise Chang, MD
2005, WebMD Inc. All rights reserved.
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Dr. Leukoma
medicine forum Guru


Joined: 30 Apr 2005
Posts: 1283

PostPosted: Fri Jul 21, 2006 12:10 pm    Post subject: Re: New Contacts, Old Infections. Warning for extended wear contacts! Reply with quote

acemanvx@yahoo.com wrote:

Quote:

Overall, the yearly rate of corneal infections was 18 per 10,000
people, the study shows.

That's similar to rates previously reported for conventional,
extended-wear soft lenses worn for fewer consecutive nights, according
to the researchers.

No. This is not a correct conclusion.

The incidence of microbial keratitis is much higher in prospective
studies than it is in retrospective population studies. In
retrospective population-based studies, the incidence of microbial
keratitis in conventional hydrogel overnight lens wear is 1/500 per
year. In a large, multicenter prospective study, the incidence is
1/210 per year, nearly twice as great. Therefore, one should be
comparing apples to apples and not apples to oranges, and comparing an
annual incidence of 1/600 for silicone-hydrogel, vs. 1/210 for
conventional hydrogel.

Also, different classification schemes for corneal infiltrates yields
different results. Some corneal infiltrates are sterile. At the very
least, silicone-hydrogel lenses are 3 times safer.

Finally, do not make the erroneous conclusion that overnight RGP lens
wear is the same as overnight OK lens wear just because the lens
materials are the same.

DrG
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