PURPOSE: The mechanical impact of silicone hydrogel contact lenses (SHCL) on corneal surface has been considered and the surface structure of these lenses could be important in several aspects of clinical response of the ocular surface. Scanning electron microscopy (SEM) has been previously applied to contact lens polymers, as well as atomic force microscopy (AFM). The purpose of this study was to observe different silicone hydrogel contact lens materials by three microscopic techniques in order to identify which one give us more representative information of the surface polymer structure.

METHODS: Contact lens materials included lotrafilcon A, balafilcon A and galyfilcon A. Microscopic techniques used in this study were AFM, SEM and cryo–scanning electron microscopy (cryoSEM). AFM statistics (tapping mode) including mean roughness (Ra) and maximum high (Rmax) were explored for the three lens materials.

RESULTS: The three materials showed a different surface configuration when observed by either method of microscopy. However, AFM technology allows us to study the sample in the hydrated state which is very important with hydrogels. AFM also allow us to study portions of the surface as small as 0.25 square microns with high resolution. Resolution at high magnification was one of the major limitations of SEM and CryoSEM, which also induce serious damage to the sample during the preparation–fixation process. However other features have been observed with these two methods that had not been reported before, particularly with cryoSEM. AFM statistics revealed a significantly more irregular surface of the Balafilcon A material (Ra=6,44nm;Rmax=96,82) when compared with Lotrafilcon A (Ra=2,40nm;Rmax=40,89) and Galyfilcon A (Ra=1,40nm;Rmax=15,33), for a 1 µm2 area.

CONCLUSIONS: The present study addresses the microscopic comparison of current SHCL pointing out the benefits of each technique. It also shows the value of cryoSEM for the study of polymeric samples from contact lenses. Present observations could have implications in clinical aspects of contact lens wear as material spoliation, resistance to bacterial adhesion or mechanical interaction with the ocular surface.