Two methods of examining protein deposits on hydrophilic contact lenses

Our aim in these studies has been to develop spectroscopic techniques for quantitative analysis of the early phases of protein deposition on soft contact lenses. We produced protein deposition in vitro by soaking lenses in a 0.025% chloral hydrate lysozyme solution at 37 degrees C. Two groups of lenses were so treated: one for 15 days and the other for 6 months. The study of in vivo deposits was carried out on lenses used by healthy wearers. From the same six patients we obtained two consecutive groups of 12 lenses: one group worn for 8 hours and the other group worn for 7 days. We tested the lenses by an indirect (destructive) method (based on a colorimetric assay of amino acid complexes obtained by basic hydrolysis) and by a direct (non-destructive) method consisting of spectrophotometry performed on intact lenses. Using the indirect method we found that the lenses absorbed in vitro for 6 months had lysozyme deposits of 5 +/- 1 micrograms; while the lenses adsorbed for 15 days supplied an average of 0.8 +/- 0.3 micrograms of lysozyme. Lenses worn by healthy volunteers show protein deposition equivalent to a lysozyme quantity ranging from 0.8 to 1.6 micrograms. We found a lower limit of detection with the direct method of approximately 5 micrograms, limiting its applicability.