Characterization of lacrymal component accumulation on worn soft contact lens surfaces by atomic force microscopy

The purpose of this study was to investigate lacrymal component accumulation on a soft contact lens (SCL) surface after various periods of continuous wear, using the recently developed atomic force microscopy (AFM). AFM allowed high resolution images of unworn and worn SCL, and presented two main advantages. 1. The SCL are analysed under nearly physiological conditions without being dried or destroyed. So the same SCL was analysed at various times during a long wearing period. To identify the deposited tear proteins, a qualitative analysis of solubilized deposit by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) on 4-15% gradient minigels was performed as well. We present typical images which emphasize the importance of the coating by lacrymal components. AFM analysis of worn SCL showed the deposition on the surface of a uniform lacrymal component coating (named deposit type I) with a progressive accumulation of numerous discrete granules (named deposit type II). SDS-PAGE of extracted deposits revealed the main tear proteins as: IgA, lactoferrin, tear lipocalin and lysozyme and the unknown protein of molecular weight 30,000. There is no clear difference in the protein patterns of the two types of deposits. Furthermore, a particular mode of use of AFM is described to illustrate the potential of this technique as a local tool for measuring protein coating thickness. Thus, for analysis of protein deposits on SCL surfaces, SDS-PAGE on minigels and AFM were easy and rapid to perform. When associated, these two techniques could find use in a wide range of worn SCL evaluation and most generally in biocompatibility evaluation studies.