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Posters | Archive
October 2005


Does the Blink Alter the Physiologically Effective Dk/t of SiH-Piggyback Contact Lens Systems?

B.A. Fink, L.N. Florkey, G. Mitchell and R.M. Hill
College of Optometry, The Ohio State University, Columbus, OH


PURPOSE: For combination systems: (1) How does the transmissibility of an SH carrier lens (vs. other materials) affect post–lens oxygenation? (2) How do cap lenses of various transmissibilities and thicknesses affect post–lens oxygenation? (3) How does blinking affect post–lens oxygenation?

METHODS: Corneal oxygen uptake rates were measured polarographically for 10 subjects (right eye only). Dk values for two GP cap lenses Fluoroperm 30 and 151, and three carrier lenses (PureVision, Permalens, and Optima 38) were 30, 151, 99, 34, and 8.4 respectively. Each cornea was measured one time and averaged with the others to obtain mean responses to 26 different exposure conditions immediately after 300 sec of wear: (1–6) FL30(0.12 mm), FL151(0.60 mm), FL151(0.12 mm), PureVision (PV), Permalens (CP), Optima 38 (Opt38) alone, no blink; (7–24) each carrier lens PV, CP, Opt38 in combination with each FL type cap lens, both with and without blinking; (25, 26) no lens and PMMA wear as controls. All responses are given as physiologically effective transmissibility (peDk/t) values based on responses ratioed 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.

RESULTS: Differences in response between non blink and blink conditions were greatest within the highest Dk/t (PureVision) carrier series, in which: (a) the lowest Dk/t (FL30) cap lens case benefited most (relatively by 3.5X) with the blink (vs. no blink); (b) a cap lens (FL151, 0 .60) of the same Dk/t as in (a), but 5X thicker, was found with that same carrier to benefit nearly identically with and without the blink; and (c) a high Dk, but thin, cap lens (FL151, 0.12) with that same carrier showed a reduced performance with vs. without blink, although both of those performances exceeded all responses in (a) and (b) Yet, none of the combination cases manifest statistically significant differences between their blink and non–blink outcomes (p value range = 0.263 to 0.924).

CONCLUSIONS: Differences, both in total thickness and in material permeability, among the combination systems observed here, appear fundamental to the relative effectiveness of the blink on oxygenation of the covered corneal surface.

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