To measure the oxygen permeability (Dk) of currently- available silicone hydrogel contact lens materials.
Permeability was measured in a randomized and masked manner for the following silicone hydrogel contact lens materials: Acuvue Advance, Acuvue Oasys, Focus Night & Day, O2 Optix and PureVision. Two conventional hydrogel lens materials, Etafilcon A and pHEMA, were measured as controls. We used an extended version of the polarographic measurement method described in ISO 9913-1. Stacks of 1-6 -1.00DS contact lenses were evaluated, with each stack measured twice. The resulting value for t/Dk (derived from electrode current and mathematically correcting for the edge effect) was plotted against t for each stack, with Dk calculated as the inverse of the gradient of this relationship; this latter method corrects for the boundary effect.
Measured permeability values (+/- 95% CI), and manufacturer- claimed values in parentheses, were: Acuvue Advance 75.2 +/- 9.8 (60), Acuvue Oasys 107.4 +/- 7.4 (103), Focus Night & Day 162.0 +/- 9.8 (140), O2 Optix 80.5 +/- 4.9 (110), PureVision 75.9 +/- 6.6 (99), Etafilcon 21.0 +/- 1.0 (21) and pHEMA 8.2 +/- 0.7 (7.5).
Our values were broadly similar to manufacturer-claimed values for the two reference materials and the Acuvue Oasys lens. It is unclear whether some manufacturers have accounted for edge and/or boundary effects, and some manufacturers may have used a different measurement methodology (coulometric); these factors may account for discrepancies between our data and that of manufacturers. Our extended ISO methodology has generated data points with small 95% confidence intervals, suggesting that the use of the polarographic method of oxygen permeability measurement can be successfully employed with hyper-permeable contact lens materials.