Lactate dehydrogenase (LDH) activity in tears was measured in 202 myopic rigid gas permeable (RGP) and 79 hydrogel human contact lens wearers and 48 normal controls by noninvasive microcapillary sampling. The oxygen permeabilities (Dk) of five selected RGP contact lenses ranged between 0 and 230 x 10-11 (cm2/s) ml O2/ml mm Hg), and the water content (WC) of the hydrogel lenses was 38, 72, and 80%. When normal diurnal variation of tear LDH activity and tear sample volume (0.3-0.6 μl) were carefully controlled, the tear LDH activity of RGP lens wearers in daily and extended wear correlated as an inverse function of Dk/L, with the highest enzyme activity observed in wearers of polymethylmethacrylate daily wear lenses (347.4 U/L). The tear LDH activity in Menicon EX (Dk 108) lens wearers was higher in the extended wear (192.7 U/L) than in the daily wear group (161.9 U/L). There was no significant difference in tear LDH activity between the Menicon SF-P (Dk 230) extended wear group (132.0 U/L) and controls (133.5 U/L). In the hydrogel lens daily wear group, tear LDH activity of Experimental 72 (WC 72%) and Experimental 80 (WC 80%) was higher than that of hydroxyethylmethacrylate (HEMA) despite having high Dk value. Experimental 80 extended wearers showed lower LDH activity in tears sampled between 0.3 and 0.6 μl than that of HEMA wearers. These results suggest that sequential measurement of LDH levels in tears may offer a new and unique method for the assessment of the physiologic effects of contact lens wear on the ocular surface, and provide a new clinical paradigm for the interaction of the contact lens with the cornea.
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