Methods used to evaluate the effectiveness of contact lens care solutions and other compounds against Acanthamoeba: a review of the literature.

PURPOSE: The purpose of this paper is to review the literature concerning the methods used to evaluate contact lens care solutions against Acanthamoeba. Acanthamoeba keratitis is a potential threat, with 85% of the cases being reported in contact lens wearers.
METHODS: Several studies from the published literature that evaluated contact lens disinfectants were reviewed. The variables included test organism, strain and morphology, growth conditions, inoculum preparation, inoculation method, test solutions and concentration, contact time, neutralization, recovery, quantitation method, and viability determination of survivors. The methods used to test Acanthamoeba against the disinfectants were compared and contrasted.
RESULTS: After a thorough review of methods used to test Acanthamoeba, it was found that there is great variability in the methods used to evaluate contact lens disinfectants. The majority of the studies used A.castellanii and A.polyphaga cysts grown axenically in PYG medium containing cations at about 30 degrees C and the inoculum contained about 1.0 x 10(5) cells/mL. Inactivation media or centrifugation of cells was used to neutralize test samples. Quantitation was performed in most studies and viability was checked in all studies. The disinfectants tested most often were PHMB, hydrogen peroxide, thimerosal, and chlorhexidine.
CONCLUSIONS: After reviewing the studies presented here it can be concluded that an effective method for testing Acanthamoeba against contact lens disinfectants would include A.castellanii or A.polyphaga grown axenically in PYG containing cations and a concentration of organisms high enough to adequately measure kill, a neutralization step, recovery and quantitation of organisms followed by a viability check of survivors.