DIFFERENTIAL ADHERENCE OF ACANTHAMOEBA TO CONTACT-LENSES - EFFECTS OFMATERIAL CHARACTERISTICS

Background. Acanthamoeba-associated keratitis occurs most often in con tact lens wearers. The contact lens material may affect its ability to act as a mechanical vector, permitting transfer of viable amoebae fro m the storage case to the corneal surface. The purpose of this study w as to investigate the effects of ionicity and water content on the com parative quantitative adherence of Acanthamoeba trophozoites and cysts to new, unworn hydrogel contact lenses and rigid gas-permeable contac t lens materials. Methods. Sixteen quarter segments of each of 8 types of unworn hydrogel lenses representative of FDA groups 1 to 4 were ex posed to freshly prepared cultures of either trophozoites or cysts of A. castellanii or A. polyphaga for 1.5 h, and then washed. Three types of rigid lens button were similarly exposed to A. castellanii trophoz oites or cysts. Adherent trophozoites and cysts were then enumerated. Results. All hydrogel lenses showed binding of both trophozoites and c ysts, with the former predominating in every case. It was primarily th e ionic nature of a lens surface and secondly its water content that w as associated with increased quantitative adherence of Acanthamoeba. N either form of the amoebae bound to any of the hard lens buttons. Conc lusions. Greater relative potential exists for contamination of ionic and high-water content hydrogels by Acanthamoeba. This combination may influence mechanical transmission of the protozoon to the corneal sur face. Adherence to hard lenses (as buttons) did not occur if a postinc ubation wash step was performed.