Acanthamoeba adherence to contact lenses and removal by cleaning agents

The quantitative adherence of a keratitis isolate of Acanthamoeba polyphaga to low- and high-water content non-ionic soft contact lenses and one type of rigid gas-permeable lens was investigated. Adherence of trophozoite and cyst forms of the organism was observed in vitro, and adherent amoebae counted by a plaque assay method following detachment. Trophozoites adhered to all lens types with adherence being statistically significantly greater to high water content soft lenses. Cyst attachment occurred only to the soft lenses but not to gas-permeable lenses, and was significantly higher for the high water content lenses. Attachment of cysts was significantly lower than that of trophozoites to each lens tested. Recommended cleaning procedures using two commercial solutions removed all adherent trophozoites and cysts from lenses. These studies demonstrate (i) that lenses may act as a vector in Acanthamoeba keratitis, particularly for high-water content lenses and trophozoite amoebae, (ii) that lens cleaning agents may prevent keratitis by removing adherent Acanthamoeba.