Influence of a Mydriatic Agent on Canine Aqueous Flare as Measured by a Laser Flare Meter

Abstract

A laser flare meter (FM-500, Kowa, Tokyo) can be used to measure protein concentrations in aqueous humor via use of a helium-neon laser. Experimentally, measurements are easier to obtain in eyes with a larger pupil size. In normal right eyes of 19 beagles, one drop of a mydriatic agent composed of 0.5% phenylephrine and 0.5% tropicamide (Mydrin P, Santen Pharmaceutical, Osaka) was administered. The left eyes were used as controls. Time course measurements were scheduled before and 0.5, 1, 2, 3 and 4 hours after the topical administration of the mydriatic agent. Pupil size was significantly increased after agent administration (Wilcoxon's rank sum test, p<0.01) and remained increased in size over the duration of the measurement period. The flare value was significantly lower 1 hour after drug administration as compared to the same measurement point for the control eyes, and remained lower throughout the rest of the measurement period (Wilcoxon's rank sum test, p<0.01). In this study, aqueous flare measurements obtained with a laser flare meter were easier to perform in mydriatic eyes as opposed to in non-mydriatic eyes due to the extension of the measurement area caused by the mydriasis. However statistically, the mydriasis significantly decreased the flare value. Hence the reliability of flare values obtained after the application of a mydriatic agent may be questionable in dogs.