title: Effect of two different cleaning methods on the back optic zone radii and surface smoothness of menicon rigid gas-permeable lenses.
abstract: OBJECTIVE
  To evaluate and compare changes to the back optic zone radii (BOZR) and the level of surface scratches of Menicon rigid gas-permeable (RGP) lenses in and between palm and digital cleaning methods and to determine whether these changes are affected by different examiners, lens materials, and initial BOZR.
  
  
  METHODS
  Ninety-six Menicon RGP lenses of two different lens materials (Menicon Z and Menicon EX) and of initial BOZR 7.6 and 8.1 mm were cleaned by two independent examiners using either palm or digital cleaning methods for a total of 270 times (simulating 9 months' use). The study was conducted with the examiners masked as to the initial BOZR and the lens material of each lens. The two examiners who investigated the BOZR and the lens surfaces were also unaware of the method of cleaning used on each lens. The BOZR and the level of scratches on lens surfaces were determined before initiating lens rubbing and after every 2 simulated months (60 cleanings) for 8 simulated months and again at the ninth simulated cleaning month.
  
  
  RESULTS
  No lens warpage was observed in any of the lenses cleaned with either method. We found no clinically significant changes in the BOZR with the number of cleanings between palm and digital cleaning methods for both the steep and the flat lenses. Changes to the BOZR were also unaffected by the examiners and the lens types. The overall mean +/- SD changes in BOZR (from baseline) after 9 simulated months were -0.014 +/- 0.025 mm for lenses using palm cleaning and -0.010 +/- 0.022 mm for lenses using digital cleaning. The level of scratches on the lenses was dependent on the examiners and the number of cleanings but was unaffected by the method of cleaning, the lens type, and the initial BOZR of the lenses. The level of scratches increased with the number of cleanings, and the median level of scratches (range) observed after 9 simulated cleaning months was grade 1.0 (0.50 to 1.50) for examiner 1 and grade 1.50 (0.50 to 2.00) for examiner 2. These values were, however, not clinically significant.
  
  
  CONCLUSIONS
  Palm or digital cleaning of Menicon RGP lenses for 9 simulated months of cleaning did not lead to any lens warpage. Changes to the BOZR with the number of cleaning were not clinically significant with either method of cleaning. Methods of cleaning, different examiners following the same procedures, lens types, and initial BOZR did not affect BOZR changes. The level of surface scratches was only dependent on the examiners and the number of cleanings. However, the changes observed were not clinically significant. Because the levels of change to the BOZR and surface scratches were comparable for both palm and digital methods of cleaning, these lenses may be cleaned using either cleaning method.
authors.affiliation: Department of Optometry and Radiography, The Hong Kong Polytechnic University, Hong Kong, SAR, China. orpaulin@polyu.edu.hk
authors.forename: Pauline
authors.initials: P
authors.lastname: Cho
authors.forename: Henry
authors.initials: H
authors.lastname: Ng
authors.forename: Ivan
authors.initials: I
authors.lastname: Chan
authors.forename: Jack
authors.initials: J
authors.lastname: Law
authors.forename: Johnny
authors.initials: J
authors.lastname: Tsang
mesh_terms: D001672:Biocompatible Materials; D018639:Contact Lens Solutions; D003261:Contact Lenses; D006801:Humans; D012826:Silicone Elastomers
chemical_list: D001672:Biocompatible Materials; D018639:Contact Lens Solutions; D012826:Silicone Elastomers