Adherence of Acanthamoeba to unworn conventional and disposable soft contact lenses

To compare the adherence of Acanthamoeba trophozoites and cysts to two types of unworn conventional and disposable contact lenses included in groups 1 and 4 of the Food and Drug Administration and to assess the adherence to the center and edge of the lenses.

We used 10 conventional and 10 disposable contact lenses belonging to groups 1 and 4 of the Food and Drug Administration. Each lens was divided into four segments. A human corneal isolate of Acanthamoeba suspended in saline (1x 105 amoebae/mL) was used. Lens segments were exposed to Acanthamoeba cysts and trophozoites for 2 hours. After removal, the count was made with an optical microscope at 100x magnification. Three fields at the center and three fields at the edge were read on each segment.

Acanthamoeba adhered to both types of contact lenses, with a proportion of trophozoites to cysts between 6:4 and 7:3. There was a significantly higher adherence to disposable (8.14 +/- 3.57 organisms/mm(2)) than to conventional (4.94 +/- 2.33 organisms/mm(2)) (p < 0.0001) contact lenses. We also found that the greatest adherence was to the edge of the conventional (12.05 +/- 4.03 organisms/mm(2)) and disposable (26.10 +/- 7.84 organisms/mm(2) (p < 0.0001) contact lenses.

This study shows that Acanthamoeba has varying adherence affinity for different new hydrogel contact lenses. The affinity for disposable lenses (etafilcon A) is significantly higher than that for conventional lenses (polymacon). This adherence is greater for ionic material and high water content. The use of low water content, nonionic contact lenses may reduce the adherence of Acanthamoeba. Finally, the edge may play an important role as an Acanthamoeba vector.