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Determination of protein deposits on RGP lenses by X-ray photoelectron spectroscopy
H Ichijima1, T Kawai, K Yamamoto
1Research and Development Department, Menicon Co., Ltd., Kasugai, Aichi, Japan.
Purpose:
To establish a novel and objective screening method for evaluating the cleaning efficacy of contact lens care solutions for removal of protein deposits on single rigid gas permeable (RGP) lenses.
Methods:
New and unworn RGP lenses containing no nitrogen atoms were incubated in a standard tear protein test solution. Protein deposition on lenses was determined by X-ray photoelectron spectroscopy (XPS) before and after standardized cleaning with commercially available care solutions (daily cleaners A, B) and a wetting/soaking solution or with 0.1w/v% sodium dodecyl sulfate (SDS) as a control. Cleaning efficacy was calculated based on the percentage of nitrogen atoms present in the total elements of the measured XPS scan spectrum.
Results:
Nitrogen atoms originating from residual protein deposits on RGP lenses after cleaning were determined by XPS. The cleaning efficacy of the wetting/soaking solution was lower (74%) than that of daily cleaners A and B (95%) or SDS (96%) controls.
Conclusions:
XPS determination of residual protein deposits is a novel and direct evaluation method for determining the cleaning efficacy of RGP lens care solutions for single lenses.