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B.A. Fink, L. Florkey, G. Mitchell, R.M. Hill; Combination Contact Lens Systems: Their Hypoxic Stress Levels, Apparent Reservoir Effects, and Physiologically Effective Transmissibilities, peDk/t's . Invest. Ophthalmol. Vis. Sci. 2004;45(13):1532.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: For combination systems: (1) to determine if GP lenses of the same calculated Dk/t, but different Dk and t values, cause different hypoxic stress levels with the same hydrogel lens; (2) to determine the physiologically effective Dk/t (peDk/t) values of those systems using an empirically derived graphical model. Methods: Corneal oxygen uptake rates were measured polarographically on the right eyes of 10 subjects. Dk values for two GP cap lenses (Fluoroperm 30 and 151), and three hydrogel vehicle lenses (PureVision, Permalens, and Optima 38) were 30, 151, 99, 34, and 8.4 respectively. Each cornea was measured one time and averaged over subjects to obtain mean responses to eight different exposure conditions immediately after 300 sec of wear without blinking: (1) FL30(.12 mm); (2) FL151(.6 mm); (3–5)FL30(.12 mm) with each one of the hydrogel materials; (6–8) FL151(.6 mm) with each of the three hydrogel materials. All responses are given as ratios to the non–wear rate. Repeated measures analysis of variance was used to test for significant difference and Tukey’s test for post–hoc comparisons at the p = 0.01 threshold. The physiologically effective transmissibility, peDk/t, of each combination system was estimated from a fitted model. Results:In every case when two equal Dk/t GP lenses were used here singly or in combination with hydrophilic vehicles, the thicker GP design resulted in lower post–trial rates. While such mean differences were observed consistently, they were not great enough to be significantly different (p = 0.265 to 0.897). The greater the Dk value of the hydrophilic vehicle, the greater the hypoxic outcome differences observed between these two GP cap lens series: PureVision > Permalens > Optima 38. Among combinations, the only peDk/t values that were different were those for FL30 with PureVision, FL151(.12 mm) with PureVision, and FL(.60 mm) with PureVision. Conclusions: When cap lenses of the same calculated Dk/t value, but different thicknesses were used with the same hydrogel vehicle lens, the thicker of the two systems had less associated post–wearing (at 300 sec) hypoxic stress. This outcome may be indicative of a "lens reservoir" effect, due to greater system volume. The peDk/t values derived for these systems reflected those apparent reservoir effects as well. CR:None Support:NEI/NIH T35–EY07151 to LF.
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