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Hard and soft contact lenses made out
of a material called silicone hydrogel may have a lower risk
of infections associated with their use than traditional extended-wear
lenses.
Recently, the US Food and Drug Administration
gave permission to two contact lens manufacturers to market
silicone hydrogel lenses for extended 30-day-wear soft contact
lenses. However, the material is not yet approved for use
in extended-wear hard contact lenses.
The new material makes for a safer contact
lens compared to anything else out there. Daily-wear contact
lenses and particularly extended-wear lenses -- those worn
even when sleeping -- can increase a person's risk of getting
eye infections, including the very serious condition known
as ulcerative keratitis.
The new contact lenses should reduce risk
of infection by about 10-fold. The risk should drop from 1
infection per 2,500 people who use daily-wear lenses and 1
in 500 for extended-wear lenses, to 1 in 25,000 and 1 in 5,000,
respectively.
The success of the new material lies in
its ability to let in about 6 to 7 times more oxygen than
traditional contact lenses.
The lenses also do not interfere with
the eyes' own ability to minimize bacteria's ability to bind
to the eye. If the bacteria can't bind to the eye then it
can't infect the eye.
The study, which was funded in part by
contact lens manufacturers, found that both hard and soft
lenses made of silicone hydrogel and worn continuously for
either 6 or 30 days produce "significantly less"
binding of the keratitis-causing bacteria to cells in the
eye.
The current study provides sound scientific
evidence that the high-oxygen transmissible silicone hydrogels
are safer and have less of an adverse physiologic effect on
the cornea when worn on an extended-wear basis.
Not only does the new study indicate that
the risk of ulcerative keratitis should be less likely, but
there is no significant difference in the corneal response
when these contact lenses are worn for 30 days compared with
7 days.
Ophthalmology
January 2002;109:27-40
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