Atomic force microscopy analysis of the surface roughness of intraocular lenses.

Abstract

In a recent study, De Giacinto et al.1 measure both the wettability and the surface roughness of several hydrophobic acrylic intraocular lenses (IOLs) using atomic force microscopy (AFM). Of interest, we have recently published a study that also analyzes the roughness using AFM of several modern hydrophobic IOLs.2 The results obtained in the 2 studies are quite similar in terms of the relative classification of the different IOLs according to the degree of roughness, but there are some differences in the absolute values found (root mean square [RMS] in nanometers). For example, the TECNIS IOL (Johnson & Johnson Vision) and the enVista IOL (Bausch & Lomb, Inc.) have 2.2 nm and 2.1 nm in their study,1 whereas we found for the same IOLs the RMS values of 2.5 nm and 3.8 nm, respectively.2 One of the major differences between the 2 studies is that De Giacinto et al. performed the AFM analysis in a dry environment, whereas in ours the IOLs were fully hydrated and the AFM analysis was performed in a fully deionized water bath.2 Of interest, we have previously shown that the surface roughness of hydrophobic IOLs increases significantly when the measurements are performed in liquid and with the IOLs fully hydrated, instead of under air and on dry IOLs.A We truly believe that, to establish the actual surface roughness of any IOL, it is mandatory to analyze the IOL samples in a fully hydrated state because it is the natural environment of the IOL when implanted inside the eye. It may be argued that this is not important as long as all the IOLs compared are analyzed in the same state (dry or hydrated). Nevertheless, we have to consider that not all hydrophobic IOLs have the same water content, so it might well be that not all the IOLs behave in an identical way regarding the surface roughness measurements. This may explain why the RMS value for the TECNIS was almost identical in both studies,1,2 but the value we found for the enVista2 is almost double than that reported by De Giacinto et al.1 Furthermore, other authors3 have obtained for the TECNIS IOL much higher RMS values than those we reported. In this study, the IOL roughness was measured in a balanced salt solution bath,3 instead of deionized water.2 This high RMS value might be explained by the fact that although the degree of the water content of the IOLs should be the same when they are in a bath of deionized water or a balanced salt solution; in the latter, tiny salt crystals may deposit on the IOL surface, and this artifact may increase the roughness. We do believe that, for several reasons, the surface roughness of the IOLs is relevant and that it is going to be a standard method to evaluate the quality of the manufacturing process. In addition, there should be a consensus about the best method to evaluate it, and we truly believe that the surface roughness should be measured on fully hydrated IOLs and in a deionized water bath.