Surface morphology of contact lenses probed with microscopy techniques

Abstract 

The present study is bringing a comparison of surface morphology for various types of contact lenses. A novel method – scanning electron microscopy under aqueous conditions (cryo-SEM) – was tested for visualization of lenses at magnifications up to 2000×. For imaging lens surface on nanometre scale, we employed atomic force microscopy (AFM) in aqueous media.

Various materials of lenses, based on silicone hydrogels or conventional hydrogels, were investigated. Total, 10 types of contact lenses from five manufacturers were selected and probed. We found that different methods of lens manufacture (lathe-cutting, cast-moulding, and spin casting) led to different values of surface roughness. In the swollen state, roughness values of lens surfaces lie between 4 and 140nm. Lenses manufactured by lathe-cutting exhibit notable higher values, so that they could be easily distinguished from others. In cast-moulded lenses, the surface roughness decreased with increasing water content. Moreover, additional treatments of lenses introduced unique structural motifs onto surface. For instance, porous structure was found on lens surface finalized with plasma oxidation.

Keywords: Atomic force microscopy, Scanning electron microscopy, Surface roughness, Contact lenses, Silicone hydrogels, Cast-moulding, Spin casting, Lathe-cutting