A team of researchers led by the Johns Hopkins
Wilmer Eye
Institute has determined that the corneal infection
rate associated with the use of 30-day extended-wear
contact lenses made from silicone hydrogel is comparable to
that previously reported for older lens types worn for
fewer consecutive 24-hour periods.
The study, published in the Dec. 1 issue of
Ophthalmology, recruited 6,245 patients, 64 percent
of them women with an average age of 35, from 131 practices
in North America between August 2002 and July 2003. All
participants were prescribed and fitted with CIBA Vision
Night & Day silicone hydrogel soft contact lenses, to be
worn for 30 consecutive 24-hour periods.
Participants completed a baseline survey to collect
information and potential risk factors for infections. At
three and 12 months after enrollment, information regarding
contact lens-wearing schedules, discontinuation of lens
wear and the occurrence of red and painful eye infection
requiring medical attention was obtained.
Eighty percent of the participants in the study
completed 12 months of lens wear and wore their lenses for
three or more weeks continuously. The overall annual rate
of evident corneal infection was 18 per 10,000. There were
two cases of corneal infection with partial loss of vision
and an additional eight cases without vision loss. The rate
of infection was lower for users wearing the lenses for
three or more weeks than for those wearing the contact
lenses for less than three-week continuous periods.
"The incidence of vision loss as a result of corneal
infections among users of the silicone hydrogel contact
lens was low," said lead investigator Oliver Schein, the
Burton E. Grossman Professor of Ophthalmology at Wilmer.
"The overall rate for corneal infection with the wearing
schedule of the silicone hydrogel soft contact lenses for
up to 30 nights was similar to that reported for
conventional extended-wear soft lenses worn for fewer
consecutive nights."
Contact lenses are safe but have some risks not
associated with glasses, Schein said. "Daily-wear rigid
gas-permeable contact lenses appear to have the lowest risk
for corneal infection, followed by daily-wear soft contact
lenses and seven- or 30-day-wear soft contact lenses,"
Schein said. "Not everyone can wear the lenses successfully
for a full 30 nights, but the risk of infection does not
appear to increase with a greater number of consecutive
nights of wear. This is a different pattern than we
previously observed with conventional extended-wear soft
lenses, where the risk did go up substantially with
additional overnight use."
The study also points out that there are many choices
for those who do not want to wear spectacles to correct
their vision, including hard and soft daily-wear contact
lenses and refractive surgery.
"Individuals tend to make choices based on factors
such as comfort, convenience, personal preference and
safety," Schein said. "The data are solid that the risks
are least with rigid and soft daily-wear contact lenses,
more with overnight wear of contact lenses and most with
refractive surgery."
The current study's results should be viewed in light
of the first studies to evaluate the original 30-day
extended-wear lenses, which were approved by the FDA in
1981. Prior to their approval, the original extended wear
lenses had been shown in studies to be relatively safe, but
as their popularity increased, many cases of corneal
ulcers, caused by bacterial infection, resulted in severe
vision loss for users.
Studies in the late 1980s showed that the risk of
infection was four times greater for the first-generation
extended-wear soft contact lenses compared to daily lenses.
The risk of infection increased as the duration of
consecutive use increased. As a result, the FDA reduced the
allowed wearing time for extended-wear contact lenses to
just seven consecutive days.
In 2001, the FDA approved CIBA Vision's silicone
hydrogel soft contact lenses for continuous wear up to 30
nights. These silicone hydogel lenses allow greater than
four times more oxygen through the lenses than did the
original extended-wear soft contact lenses and are
therefore thought to offer health benefits for the cornea.
However, because of the complications seen in the 1980s
with the original extended-wear soft contact lenses, the
FDA mandated post-market surveillance studies for these new
lenses, which the current study satisfies.
Other Johns Hopkins researchers who participated in
the study are James M. Tielsch and Joanne Katz, both of the
Bloomberg School of Public
Health.
The study was supported by a research grant from CIBA
Vision to fulfill the FDA-mandated post-market surveillance
requirement for new 30-day extended-wear lenses. None of
the Johns Hopkins researchers has a consultative or
proprietary interest in the product or company.
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