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.
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.
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:
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
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