Researchers led by the Johns Hopkins Wilmer Eye Institute have 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 journal 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 Oliver Schein, lead investigator of the study and the Burton E. Grossman at the Johns Hopkins Wilmer Eye Institute. " 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 ( HEMA ) extended-wear soft lenses worn for fewer consecutive nights," he added.
Contact lenses are safe, but have some risks not associated with glasses, added Schein. " 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," said Schein. " Not everyone can wear the lenses successfully for a full 30-nights, but the risk of infection does not appear to increase with 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, such as LASIK ( laser-assisted in situ keratomileusis ).
" Individuals tend to make choices based on factors such as comfort, convenience, personal preference and safety," notes Schein. " 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," he adds.
The 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 be offer health benefits for the cornea.
However, because of the complications seen in the 1980s with the original extended-wear soft contact lenses and therefore the FDA mandated post-market surveillance studies for these new lenses.
Source: Johns Hopkins Medical Institutions, 2005