Contact Lenses Designed for Extended Use May Reduce Infection Risk
(HealthDay News) – In the late 1980s, extended use contact lenses were viewed skeptically by many ophthalmologists. At that time the theory was, the longer you wear them, the better the chance for developing an infection, especially a bacterial one.
The worries about infections are gone, says a contact lens expert because the new lenses are made of materials that repel bacteria much better than the older materials did.
In 2002 the U.S. Food and Drug Administration approved three of these lenses for up to 30-night extended wear, says Dr. H. Dwight Cavanagh, of the University of Texas Southwestern Medical Center at Dallas . His research team looked at all three new lenses, evaluating whether they cause more bacteria to bind to the surface of corneal cells -- a measure of infection risk -- than did conventional daily wear lenses or extended wear lenses. In all, more than 800 contact lens wearers were studied.
In 2006, a bacterial outbreak associated with contact lenses occurred, but it had to do with a lens solution marketed as ReNu with MoistureLoc, and not with the contact lenses themselves,
Lenses evaluated include the Bausch & Lomb Pure Vision, Ciba Vision Night & Day and Menicon Z lens. Pure Vision and Night & Day are soft lenses, while the Z is a rigid lens.
Whether people wore the lenses for six nights or 30, there was either no risk or only slightly increased risk that the organism Pseudomonas aeruginosa -- the bacterium linked to the most and worst lens-related corneal infections -- would bind to the corneal cells. The rigid lens performed better than the soft lens, Cavanagh reports.
"The length of wear doesn't seem to matter," he says. In fact, the new lenses produce less infection risk than daily wear or extended wear lenses in use today.
With the new lenses, he says, the risk of an eye infection declines "by a factor of 10 and maybe even 40."
His studies, funded by the National Eye Institute and manufacturers of the new lenses, were published in a 2002 issue of Ophthalmology .
So safe are the newer materials, Cavanagh says, that even contact lens wearers who don't intend to sleep in their lenses should consider switching to the newer materials to minimize infection risk.
About 35 million Americans wear contact lenses, according to estimates by the Contact Lens Council. An expert on corneal infections calls the studies impressive.
"There's hope," says Richard J. O'Callaghan, professor and c hairman of the University of Mississippi 's department of microbiology in Jackson . "He's talking about a major change in the frequency of infection [with the use of the new extended wear lenses]."
Eliminating bacteria from gaining access to the cornea and sticking to the lens, he says, should greatly reduce infection.
Not everyone can get fitted properly with the new lenses. Some models are not yet made to correct astigmatism, an inability of the eye to focus sharply due to an abnormally shaped cornea. And they are not yet available as disposables, although Cavanagh expects they will be in the future.
The new extended wear lenses "offer options," Cavanagh says, and for some will be an alternative to LASIK.
While the risk of infection with the new extended wear lenses is less, they are not maintenance-free. "You will have to clean all of them," Cavanagh says. Also, some wearers may have a problem with allergies to the material.
On the Web
For more information on contact lenses, see the Contact Lens Council, which has a section on frequently asked questions about contact lenses.
SOURCES:
H. Dwight Cavanagh, M.D., Ph.D., professor and Dr. W. Maxwell Thomas Chair in Ophthalmology, University of Texas Southwestern Medical Center, Dallas; Richard J. O'Callaghan, Ph.D., professor and Chairman, Department of Microbiology, University of Mississippi Medical center, Jackson; Sept. 24, 2002, presentation, Research to Prevent Blindness meeting, Washington, D.C.
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Author:
Kathleen Doheny, HealthDay Reporter
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