title: Determination of protein deposits on RGP lenses by X-ray photoelectron spectroscopy.
abstract: OBJECTIVE
  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.
authors.affiliation: Research and Development Department, Menicon Co., Ltd., Kasugai, Aichi, Japan.
authors.forename: H
authors.initials: H
authors.lastname: Ichijima
authors.forename: T
authors.initials: T
authors.lastname: Kawai
authors.forename: K
authors.initials: K
authors.lastname: Yamamoto
authors.forename: H D
authors.initials: HD
authors.lastname: Cavanagh
mesh_terms: D018639:Contact Lens Solutions / Q000494:pharmacology; D003261:Contact Lenses; D004577:Electron Probe Microanalysis / Q000379:methods*; D005136:Eye Proteins / Q000032:analysis* / Q000378:metabolism*; D006801:Humans; D009584:Nitrogen / Q000032:analysis*; D011485:Protein Binding / Q000187:drug effects
chemical_list: D018639:Contact Lens Solutions; D005136:Eye Proteins; C042434:tear proteins; D009584:Nitrogen