Think you're sterilizing your contacts when you soak them in fluid overnight? Here's some unwelcome news: Most contact lens solutions do not kill the type of amoeba that causes severe eye infections, according to researchers at the Centers for Disease Control and Prevention.
Out of 11 solutions tested, the only two that disinfected against the bugs after four to six hours were the two that contained hydrogen peroxide.
Contact lens wearers are warned about the rare but serious disease known as Acanthamoeba keratitis, caused by amoebae found in soil, freshwater, seawater, hot tubs, and Jacuzzis. The infection, which is associated with improper lens care, can lead to ulceration of the cornea, loss of vision and, ultimately, blindness.
In the study, researchers looked at three species of amoebae that frequently cause the infection. They added solutions containing dormant, inactive forms (cysts) from each of these species to 11 different brands of contact lens solutions. The cysts were soaked in lens solution for between four to six hours (depending on the manufacturer’s soaking time instructions) or 24 hours. The scientists then watched for two weeks to see which cyst solutions resulted in the growth of active, disease-causing amoebae.
Of the 11 solutions, Ciba Vision Clear Care showed the greatest effectiveness against cysts of all three amoeba species: Two species did not grow at all after their cysts were soaked for either six or 24 hours, and the third species had growth reduced by two-thirds after being soaked for six hours (and no growth after being soaked for 24 hours).
Ciba Vision Clear Care and another, Advanced Medical Optics UltraCare, the two solutions containing hydrogen peroxide, were the only solutions that showed disinfection ability after six hours.
After 24 hours, several non-hydrogen-peroxide-containing solutions showed some signs of effectiveness against either one or two species -- but not enough to be considered statistically significant: Bausch & Lomb Boston Simplus, Bausch & Lomb ReNu MoistureLoc, Ciba Vision AQuify, and Kirkland Signature Multipurpose Solution. And even if the findings had been statistically significant, it isn't clear how practical they would be. After all, most lens wearers do not soak lenses longer than overnight.
The study’s inspiration came from the international recall in 2007 of the multipurpose lens solution Advanced Medical Optics Complete MoisturePlus, when it was found to be associated with Acanthamoeba keratitis. When tested in this study, the lens solution did not show any effectiveness in killing any of the three species.
“Currently, it is not required to demonstrate killing Acanthamoeba before a lens solution can be licensed,” says study coauthor Jonathan Yoder of the Division of Parasitic Diseases at the CDC.
Complicating the situation is the fact that the Food and Drug Administration does not provide guidelines for testing the effectiveness of lens solutions against amoeba species. As a result, studies have differed in their procedures and strains of amoeba used.
Yoder says the findings should help the FDA in its review of whether contact lens solutions should be required to kill Acanthamoeba.
-- Shara Yurkiewicz