Surface treatment or material characteristic: the reason for the high level of Acanthamoeba attachment to silicone hydrogel contact lenses

Purpose. To determine the reason for the high level of attachment of Acanthamebic to silicone hydrogel (SH) contact lenses. The effect surface treatment has on attachment is determined using silicone elastomer (SE) lenses. Methods. All test lenses were unworn. SH (PureVision), conventional hydrogel (Acuvue), treated SE (Silsoft), and untreated SE (Silsoft) lens quarters were incubated for 90 min with plate-cultured Acanthamoeba castellanii trophozoites. After incubation and rinsing, the trophozoites attached to one surface of each quarter were counted by direct light microscopy. Sixteen replicates were performed for each lens type. Logarithmic transformation of data allowed the use of parametric analysis of variance. Results. Lens polymer had a significant effect on attachment (P <0.001), with higher numbers of trophozoites attaching to the SH and SE (treated and untreated) lenses as compared with the conventional hydrogel. No significant difference in attachment was detected between the SH and SE (treated and untreated) lenses. Conclusion. Acanthamoeba attachment to the SH lens was significantly greater than to the conventional hydrogel. The similarity in attachment to surface-treated and non-surface-treated SE lenses suggests that the increased attachment found with the SH lens may be an inherent characteristic of the polymer rather than an effect of the surface treatment procedure. It is possible that SH lenses are at greater risk of promoting Acanthamoeba infection if exposed to the organism because of the enhanced attachment characteristic of this new material.