Some Contact Lens Solutions Aren't
Potentially blinding bug survives some cleansers, says study
TUESDAY, Jan. 29, 2002 (HealthDayNews) -- Certain contact lens cleaners may not be enough to kill off a common organism that can cause eye infections, says new research.
A study of disinfectant cleaning solutions found that only two-step hydrogen peroxide systems destroyed the Acanthamoeba organism on soft and rigid contact lenses. This organism can cause keratitis of the eye among lens wearers, leading to pain, sensitivity to light and even blindness.
The findings should be a wake-up call for lens wearers who are lax about lens hygiene, says Horst Aspöck, the study's senior investigator and head of medical parasitology at the Clinical Institute of Hygiene in Vienna.
"Many people do not take adequate care of their contact lenses," he says, adding that a two-step system appeared to be particularly important for cleaning soft contact lenses.
Experts say the risks associated with an Acanthamoeba infection stress the importance of maintaining strict contact lens hygiene.
Acanthamoeba is a single-celled organism that lives worldwide in soil and water. It has also been found in heating, venting and air conditioning units, as well as in contact lens equipment.
The organism has two life stages. In its active cycle, Acanthamoeba trophozoites move, feed and divide, but the organism forms protective cysts in times of hardship.
According to Acanthamoeba expert Simon Kilvington, a lecturer in microbiology and immunology at the University of Leicester in England, the hardier cysts can be transported by wind or water currents, but they will release trophozoites again if conditions improve.
In the February issue of the British Journal of Ophthalmology, researchers at the University of Vienna tested the effect of three types of disinfectants on three strains of Acanthamoeba.
After lenses were soaked for eight hours in the first disinfectant, known as a multipurpose solution, the researchers found all of the trophozoites were killed. However, cysts from two of the three Acanthamoeba strains survived the disinfecting process.
The second cleaner was a one-step hydrogen peroxide solution. Since hydrogen peroxide would burn the eye, a neutralizing compound must be added before a cleaned lens can be reused. In a one-step solution, this neutralizer is added in the form of a dissolving tablet along with the hydrogen peroxide.
Although this system killed the Acanthamoeba trophozoites, cysts from all three of the strains survived.
Kilvington blames it on the neutralizing compound.
"Unfortunately, they neutralize the peroxide too quickly, so it doesn't get much of a chance to kill very resistant organisms like Acanthamoeba cysts," he says.
Finally, the researchers tested a hydrogen peroxide two-step solution, in which the lens were soaked in hydrogen peroxide for eight hours, then rinsed in a neutralizing solution for 10 minutes. This solution killed both the Acanthamoeba trophozoites and cysts.
"Only the two-step system will guarantee that all cysts of the Acanthamoeba strains which we have tested will be killed," says Aspöck.
Kilvington adds it's also crucial to prevent lens contamination from contact lens storage cases.
"You can get a large buildup of bacteria inside these storage cases," he says. "If an Acanthamoeba cyst gets inside there, it can hatch out because the bacteria are present, [and] it can feed and multiply on the bacteria."
The disinfectant solutions are meant to clean the lenses and the case simultaneously, but Kilvington says that disinfection can't be confused with sterilization.
Both Kilvington and Aspöck agree contact lens storage cases should be replaced every four weeks. While it is an added expense, says Aspöck, "better to spend money for this than go blind, which is possible in extreme cases."
What To Do: Check out this diagram of the eye from the National Eye Institute to learn the basics, then visit the University of Utah or Centers for Disease Control and Prevention to find out more about the Acanthamoeba organism.