COLOR-VISION AND SIDE-EFFECTS DURING TREATMENT WITH METHAZOLAMIDE

The retina contains Na+K+-ATPase and carbonic anhydrase (CA), enzymes that regulate ion fluxes across cell membranes of photoreceptors. Sinc e inhibition of retinal Na+K+-ATPase by digitalis impairs colour visio n, we wanted to find out whether this also occurs after inhibition of CA. In a double-masked crossover study with placebo, 14 male volunteer s were given 50 mg q.i.d. of the CA inhibitor methazolamide for 2 week s. A disturbance of colour discrimination was observed in 8 of the 14 subjects, in the classification phase of Lanthony New Color Test. The presence of the disturbance was not significantly correlated to the de gree of acidosis or to other side-effects. Its mechanism could be inte rpreted as a specific effect of CA inhibition in the retina (or the vi sual cortex) calculated to more than 99.9%.