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Oxygen permeability and water content of silicone hydrogel contact lens materials

by Nathan Efron, Philip B Morgan, Lan D Cameron, Noel A Brennan, Marie Goodwin
  • ISSN: 1040-5488


Purpose. To measure the oxygen permeability (Dk) and water content (WC)\nof silicone hydrogel (Si-Hy) contact lens materials.\nMethods. Randomized and masked determinations of the Dk of 5 Si-Hy and\ntwo hydrogel materials were made using a modified version of the\npolarographic measurement method described in ISO 9913-1. Stacks of one\nto six parallel-sided contact lenses (all -1.00 DS) were evaluated, with\neach stack measured at least twice. The resulting value for t/Dk was\nplotted against the thickness (t) of each stack, with Dk calculated as\nthe inverse of the gradient of this relationship. This methodology\ncorrects for boundary effects. A mathematical calculation was used to\ncorrect for edge effects. Gravimetric determination of lens WC was\nconducted at room temperature and 35 degrees C.\nResults. Measured values (+/- 95% CI) of Dk, and WC at room\ntemperature, with manufacturer-claimed values in parentheses, were Focus\nNight & Day: Dk 162.0 +/- 9.8 (140), WC 23.0 +/- 3.2 (24); Acuvue\nOasys: Dk 107.4 +/- 7.4 (103), WC 36.9 +/- 1.0 (38); 02 Optix: Dk 80.5\n+/- 4.9 (110), WC 32.1 +/- 1.2 (33); PureVision: Dk 75.9 +/- 6.6 (91),\nWC 35.8 +/- 1.3 (36); Acuvue Advance: Dk 75.2 +/- 9.8 (60), WC 46.5 +/-\n1.1 (47); 1.Day Acuvue: Dk 21.0 +/- 1.0 (21.4), WC {[}not measured]\n(58); and Seequence: Dk 8.2 +/- 0.7 (8.5), WC 36.6 +/- 2.7 (38).\nConclusions. Claimed Dk values for Acuvue Oasys and the two reference\nhydrogel materials fell within the 95% confidence interval of our\nmeasured values. Our measurements of Dk for the other four Si-Hy lenses\nwere not in agreement with claimed values. There is a general inverse\nrelation between Dk and WC (both at 35 degrees C) for Si-Hy lenses. Our\nmodified polarographic methodology can be successfully employed for\nmeasuring the Dk of Si-Hy materials.

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