The effect of center thickness and material permeability on the hypoxic stress induced by rigid gas permeable and hydrogel contact lenses
Abstract (Summary)The purpose of this study was to assess the oxygen transmitting performance of a high Dk rigid gas permeable material, Fluoroperm 15 1, and two hydrogel materials, Aqua-Sphere 53 and AL-47, during wear by human subjects. Hypoxic stress units (HSU’s) were used to describe the performance of these materials over center thicknesses from 0.08 mm to 0.32 mm at a constant back vertex power of -3.00 DS. HSU’s are relative corneal oxygen uptake rates where zero HSU’s is equivalent to the oxygen uptake rate of the open eye, and 100 HSU’s represents the maximum oxygen uptake rate induced by static wear of an oxygen-impermeable polymethyl methacrylate contact lens. A Clark-type polarographic electrode was used to measure the oxygen uptake rates in each of these conditions. The relationship between HSU’s and center thickness (CT) for Fluoroperm 15 1 (Dk = 15 1 x lo(-1 1) (cm2/s)(ml02/ml x mrnHg)) was well described (R2 = 0.965) by the linear equation: HSU’s = 1.5755 + 46.685 (CT). This represented a statistically significant improvement over Fluoroperm 92 (Dk = 92 x l0(- 1 1) (cm2/s)(ml 02/ml x rnmHg)) at center thicknesses greater than 0.12 mm. When comparing HSU results from Fluoroperm 15 1 to the Hypoxic Response Line, a statistically significant departure from that line was found at a Dk/L of 64.5 x l0(-9) (cm/s)(ml02/ml x rnrnHg) and above. The relationship between HSU’s and center thickness for Aqua-Sphere 53 (Dk = 18.1 x lo(- 1 1) (cm2/s)(ml02/ml x mrnHg)) had a regression line of: HSU’s = 18.320 + 164.86 (CT). Linearity was not as strong in this case with R2 = 0.882. For AL-47 (Dk = 3.7 x l0(-1 1) (cm2/s)(ml02/ml x mrnHg)), the regression line was: HSU’s = 54.636 + 104.05 (CT). This was more linear than Aqua-Sphere 53 with R2 = 0.923. Each hydrogel material may have performed better than was predicted for rigid gas permeable materials for the same Dk/L levels, as predicted by the Hypoxic Response Line. However, the difference could not be confirmed statistically.
School:The Ohio State University
School Location:USA - Ohio
Source Type:Master's Thesis
Date of Publication:01/01/1996