OXYGEN PERMEABILITY (Dk) OF REFERENCE MATERIALS

Abstract

Purpose : The Permeability Reference Material Repository is depleted of the original 7 reference materials denoted R1 to R7. Dk values for these materials were reported in Invest. Ophthalmol. Vis. Sci. 2006; 47(13):97. Materials denoted R8 to R12 in single lots were recently supplied by 3 manufacturers of rigid contact lens materials.

Methods : Seven sites having the apparatus, calibrating specimens, and versed in the measurement and calibration of Dk according to the International Organization of Standardization (ISO) 18369-4:2017 and American National Standards Institute (ANSI) Z80.20-2016 determined the Dk of materials R8-R12. A set of R8-R12 reference samples was sent to each of the sites. They were monocentric, uniform-thickness lenses in nominal thicknesses of 0.11, 0.14, 0.18, 0.23, 0.29, and 0.40 mm such that the linearity between oxygen resistance (t/Dk) and thickness (t) could be inspected. Buttons were manufactured into samples by Valley Contax, Inc. (Springfield, Oregon, USA). The diameter was 10.0mm and back curve radius 7.80 or 8.60mm depending on the electrode in use at each site. To reduce fracture during handling, the thinner samples (0.11, 0.14mm) had thicker peripheries produced by a minus carrier and front junction of 8.0mm diameter.

Results : Reference Dk values were taken as the mean calibrated Dk values (n = 7) of the R8 to R12 materials. For R8: mean 68.7, Standard Error of the Mean (SEM) 2.4, 95% Confident Limits (CL) 64.0-73.5 Fatt Dk units; for R9: mean 120.8, SEM 5.9, CL 109.2-132.5 Fatt Dk units; for R10: mean 161.2, SEM 5.4, CL 150.5-171.9 Fatt Dk units; for R11: mean 145.2, SEM 6.5, CL 132.6-157.9 Fatt Dk units; and for R12: mean 171.7, SEM 4.9, CL 162.1-181.3 Fatt Dk units. Linear regressions between the Dk values from each site and the reference Dk values resulted in coefficients of determination (R²) ranging from 0.9448 to 0.9922. Three of 7 were above 0.9900. The carrier of the 0.11 and 0.14mm samples did not appear to influence the linearity of t/Dk vs. t.

Conclusions : Dk values from different operators and sites assessing different sets of samples were highly correlated linearly with the reference values. The order of Dk progression for the materials from low to high was the same at each site. The spread of Dk values for each material supported the Dk measurement error (±10%) and tolerance (±20%) in the ISO and ANSI standards.

This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.