To measure the oxygen permeability (Dk) and water content (WC) of silicone hydrogel (Si-Hy) contact lens materials.
Randomized and masked determinations of the Dk of 5 Si-Hy and two hydrogel materials were made using a modified version of the polarographic measurement method described in ISO 9913-1. Stacks of one to six parallel-sided contact lenses (all –1.00 DS) were evaluated, with each stack measured at least twice. The resulting value for t/Dk was plotted against the thickness (t) of each stack, with Dk calculated as the inverse of the gradient of this relationship. This methodology corrects for boundary effects. A mathematical calculation was used to correct for edge effects. Gravimetric determination of lens WC was conducted at room temperature and 35°C.
Measured values (±95% CI) of Dk, and WC at room temperature, with manufacturer-claimed values in parentheses, were Focus Night & Day: Dk 162.0 ± 9.8 (140), WC 23.0 ± 3.2 (24); Acuvue Oasys: Dk 107.4 ± 7.4 (103), WC 36.9 ± 1.0 (38); O2 Optix: Dk 80.5 ± 4.9 (110), WC 32.1 ± 1.2 (33); PureVision: Dk 75.9 ± 6.6 (91), WC 35.8 ± 1.3 (36); Acuvue Advance: Dk 75.2 ± 9.8 (60), WC 46.5 ± 1.1 (47); 1.Day Acuvue: Dk 21.0 ± 1.0 (21.4), WC [not measured] (58); and Seequence: Dk 8.2 ± 0.7 (8.5), WC 36.6 ± 2.7 (38).
Claimed Dk values for Acuvue Oasys and the two reference hydrogel materials fell within the 95% confidence interval of our measured values. Our measurements of Dk for the other four Si-Hy lenses were not in agreement with claimed values. There is a general inverse relation between Dk and WC (both at 35°C) for Si-Hy lenses. Our modified polarographic methodology can be successfully employed for measuring the Dk of Si-Hy materials.
Institute of Health and Biomedical Innovation, and School of Optometry, Queensland University of Technology, Kelvin Grove, Australia (NE), Eurolens Research, The University of Manchester, Manchester, United Kingdom (PBM, IDC, MG), and Brennan Consultants, Melbourne, Australia (NAB)
Received May 4, 2006; accepted September 26, 2006.