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LN Florkey, BA Fink, GL Mitchell, RM Hill; Examination of Dk/t in Combination Contact Lens Systems Involving PMMA . Invest. Ophthalmol. Vis. Sci. 2002;43(13):3085.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Combination contact lens systems can be an effective refractive option in cases of corneal surface irregularity, but physiological success may be dependent upon the choice of lens components. Here, the performance of four soft lens types of varying Dk/t are compared under the limiting condition of a polymethylmethacrylate (PMMA) rigid material (Dk/t = 0). Methods: Corneal oxygen uptake rates were measured for the central cornea of ten human subjects with a polarographic electrode. Measurements were made for the normal open eye and following static wear of PMMA; a thin hydrogel, Dk/t=14 (Bausch&Lomb Optima 38); a thick hydrogel, Dk/t=13 (Coopervision Permalens); a high Dk silicone/hydrogel, Dk/t=122 (Bausch&Lomb Purevision); and a daily disposable, Dk/t=40 (Vistakon Acuvue). Additional measurements were made following static (non-blinking) and dynamic (blinking) wear of the combination of PMMA with each of the four hydrogel lenses. The lenses were worn for five-minute intervals and five-minute rest periods were given between each measurement. Results: Repeated measures analysis of variance revealed a significant difference in the mean oxygen uptake relative to air for the thirteen lenses (p<0.0001). The oxygen uptake for PMMA with Acuvue (both static and dynamic conditions) was significantly higher than PMMA with Purevision (dynamic), Optima 38, Permalens, and Purevision. PMMA worn alone was also significantly different from Optima 38, Permalens, and Purevision. Additional analyses were performed to compare oxygen uptake obtained under static and dynamic conditions. There was not a significant difference between the two conditions (p=0.1154) nor were there any differential effects of lens on the static to dynamic comparisons (p=0.6609). Conclusion: The components of these systems do have an effect on the oxygen uptake values relative to air, regardless of their Dk/t value. The lack of significance in the oxygen uptake relative to air under static and dynamic conditions indicates that the differences between the combinations apply to both the static and dynamic conditions, showing low tear exchange with blinking. Increasing the thickness or permeability of the soft lens component did not provide for a reservoir of oxygen to the cornea during lens wear.
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