Infection-Causing Amoeba May be Resistant to Multiple Contact Lens Solutions

A new study suggests that some contact lens solutions do not properly disinfect against Acanthamoeba, a free-living organism in the environment that can cause a painful vision-threatening infection. The researchers from the Centers for Disease Control and Prevention, Public Health Service, and the U.S. Department of Health and Human Services, Atlanta, Georgia, report their findings in the July 2009 issue of the Journal of Clinical Microbiology.

Acanthamoeba are found in a variety of environmental sources including soil, freshwater, brackish water and seawater, as well as hot tubs and Jacuzzis. The species is associated with many different human diseases such as central nervous system infections and Acanthamoeba keratitis (AK), an infection of the cornea that can ultimately lead to blindness. 85 percent of AK cases in the United States are attributed to contact lens wear, with some specific risk factors being improper contact lens care and contact with nonsterile water during wear.

Insufficient anti-Acanthamoeba activity in Advanced Medical Optics Complete MoisturePlus multipurpose contact lens solution was brought to attention following a recent multistate outbreak of AK. While investigating that outbreak, researchers also compared the effectiveness of 11 other contact lens solutions against cysts of Acanthamoeba castellanii, Acanthamoeba polyphaga, and Acanthamoeba hatchetti, all of which were sample specimens collected during the outbreak. Results indicated that only the two contact lens solutions containing hydrogen peroxide showed any disinfection ability against A. castellanii and A. polyphaga after six  or 24 hours. No significant disinfection efficacy was noted among the 11 solutions against A. hatchetti.

"The prevention of future cases of AK will require contact lens solutions that are effective against Acanthamoeba species and continued emphasis on proper lens care hygiene," say the researchers. "Educating contact lens wearers about the risk factors for AK, including the improper use of contact lens solutions, is important; but a systematic method for evaluating contact lens solutions will reduce the chance that inefficacious solutions are available."

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