A recent research has found that the use of a specific contact lens solution is very strongly linked to Acanthamoeba keratitis (AK), a rare severe eye infection.
The study, by University of Illinois researchers, has been published online by the American Journal of Ophthalmology.
AK is an often severe, aching infection of the cornea that normally causes corneal scarring and at times blindness.
"We began to look for possible contact lens-related causes for the sharp increase in cases, all in contact lens wearers, in this previously rare infection. In the last three and half years we have seen 63 cases of the infections, compared to the two or three cases a year we would normally expect to see," said Charlotte Joslin, assistant professor of ophthalmology and visual sciences at UIC and principle investigator in the study.
In their study, the researchers compared 38 AK patients with 100 controls, all of whom were UIC clinic patients between 2003 and 2006. In addition to this, all participants were asked to fill out a survey.
Survey questions centred on the six-month period previous to symptoms and targeted three areas: water exposure; contact lens hygiene, including solutions and lens types; and other habits associated with contact lens use. Participants were provided with colour images of the contact lens solution bottles to help them remember what type they had used.
Among soft contact lens wearers, participants with AK were considerably more likely to report having exclusively used AMO Complete Moisture Plus than the control group (55.2 percent vs. 10.5 percent).
"The results correlated with previously published laboratory studies that showed that Acanthamoeba is largely resistant to contact lens solutions in general and to Complete MoisturePlus in particular," said Dr. Elmer Tu, associate professor of clinical ophthalmology, who is also involved with the study.
In their voluntary recall, the company highlighted that there is no proof to advocate that today's voluntary recall is related to a product contamination issue.
The researchers also found a statistically fragile association between three other contact lens use factors and infection: reusing solution, rubbing the lenses when cleaning them, and showering with lenses on.
"Showering can scatter water-borne microbes into a mist and increase exposure to the microbe that causes the infection," said Joslin. Reusing solutions and not rubbing lens when cleaning and storing them could also result in more exposure to the microbe.
Since these factors are linked to an augmented probability of infection and this is the second very recent outbreak of a tremendously rare eye infection, the researchers stress that it is important to look for supplementary causes behind the occurrence of this infection and to assess whether changes in the water supply may be contributing to this increase in disease.
For example, Joslin said, recent Environmental Protection Agency regulations that reduce the levels of disinfectant in the water supply may have led to an enhance in the microbial load that contact lens solutions must kill in order to avert disease.
"Our results demonstrate that the use of AMO Complete MoisturePlus Multi-Purpose Solution is strongly associated with AK disease -- but it was not a factor in nearly 40 percent of cases," Joslin said.