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L.N. Florkey, B.A. Fink, G.L. Mitchell, R.M. Hill; Hypoxic Responses to RGP + Silicone-Hydrogel (SH) Combination Contact Lens Systems . Invest. Ophthalmol. Vis. Sci. 2003;44(13):3674.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To investigate: (1) how a SH lens under a RGP lens alters corneal hypoxia; (2) how RGP lenses of the same calculated Dk/t–but different t–may affect corneal hypoxia alone and in combination systems; and (3) contributions of the blink in reducing hypoxia under such systems. Methods: Corneal oxygen uptake rates of 10 right eyes were measured polarographically. Dk values for FL30, FL151, and the SH (balafilcon A) element were 30, 151, and 99 respectively. Each cornea was measured once under 7 exposure conditions immediately after 300 seconds of wear: (1) no lens, static; (2) FL30 (0.12mm) alone, static; (3) FL30 (0.12mm)+SH, static; (4) FL30 (0.12mm)+SH, dynamic; (5) FL151 (0.60mm) alone, static; (6) FL151 (0.60mm)+SH, static; (7) FL151 (0.60mm)+SH, dynamic. There was a 300sec rest interval between each trial, and all responses are given as ratios to the rate for no lens. Repeated measures analysis of variance was used to test for significant differences, and Dunnett’s test for post-hoc comparisons at the p=0.05 threshold. Results: Insertion of the SH lens did not reduce short-term hypoxia significantly for either the FL30 (p=0.0792) or the FL151 (p=0.0792) cases with, versus without, the SH lens. Although calculated Dk/t’s for both FL30 at 0.12mm and FL151 at 0.60mm were equal (25x10exp-9), static responses of the cornea to them differed by 20% (RGP’s alone, p=0.0282; and RGP’s+SH lenses, p=0.0282). Blinking induced a hypoxic relief of 20% in the FL30+SH case only, with little relief seen in the FL151+SH case (p=0.0792). Conclusions: (1) Addition of this SH lens did not increase corneal hypoxia significantly in either RGP system when measured statically. (2) Although the calculated Dk/t’s were equal for both thick and thin RGP lenses, the thicker manifested less hypoxia both with and without the SH element, a possible RGP "lens reservoir effect". (3) Blinking reduced hypoxia under the thinner RGP+SH system only–most likely due to lid-lens interaction differences.
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