White light interferometry to characterize the hydrogel contact lens surface

Abstract

Purpose: The aim of this study was to characterize, qualitatively and quantitatively, the surface morphology of four unworn conventional hydrogel contact lenses (Omafilcon, Hioxifilcon-based, Nefilcon A and Ocufilcon B) by White Light Optical Profiling (WLOP). WLOP is an ideal technique for sampling larger areas as well as for higher measurement speed compared with other topography techniques used in contact lens studies. Methods: Surface roughness was assessed by WLOP in the Vertical Scanning Mode, with a Wyko NT1100, which is a non-contact optical profiling system that provides high vertical resolution. Representative roughness parameters, the Average Roughness (Ra), Root-mean-square Roughness (Rms), and Maximum Roughness (Rmax), for areas of 625, 2500, 10829 and 67 646 lm2 were calculated. Results: Higher Ra, Rms and Rmax values were obtained for larger areas in all lenses. Daily disposable contact lenses (Nefilcon A and Ocufilcon B) presented the highest Ra, Rms and Rmax values, the larger changes in these parameters becoming apparent with the increase in the measured area. Differences between lenses were less obvious when data from 625 and 2500 lm2 area were compared. Conclusions: Daily disposable contact lenses showed the highest roughness surface. Analyzing larger areas might be adequate to detect differences between lenses in terms of surface characteristics, which may not be so obvious if smaller areas are studied.