To determine the surface roughness of cosmetic and conventional contact lenses (CLs) and their susceptibility to bacterial adhesion.

Concave surface roughness of cosmetic and conventional hydrogel (Etafilcon A) CLs was measured by atomic force microscopy (AFM) and scanning electron microscopy (SEM). In particular, the surface of the color tinted area of cosmetic CLs was measured. CLs were immersed into a bacterial solution of Pseudomonas aeruginosa for 1, 12, or 24 hours and culture of P. aeruginosa that had adhered to the CLs was performed.

Concave surface roughness of cosmetic CLs significantly increased compared with conventional CLs by AFM ( p < 0.05). Bacterial colony formation of P. aeruginosa adhering to cosmetic CLs within one hour significantly increased compared with conventional CLs ( p = 0.047). Adhesions of P. aeruginosa to CLs within one hour was found to correlate significantly with the surface roughness of CL (r > 0.9, p < 0.05). By SEM, P. aeruginosa had adhered to the color-tinted area more than to the non-color-tinted area of cosmetic CLs.

Surface of cosmetic CLs was significantly rougher and initial adhesion of bacteria was higher to cosmetic CLs than to conventional CLs. In particular, an increased number of bacteria was found to be adhered to the color-tinted area of cosmetic CLs. Initial bacterial adhesion is important because it is the first stage of bacterial attachment process to any surface. After then, the adherent bacteria can progress to form a biofilm. Increased surface roughness of CLs contributes to opportunities for the CL to come into contact with bacteria, and thus, initial bacterial adhesion increases. In this study, it is clear that cosmetic CLs are more vulnerable to bacterial adhesion. To avoid serious complications, such as bacterial keratitis, the manufacturing process for smoothing and treating the surface in order to inhibit bacterial adhesion should be developed in the future.