Colour vision and side-effects during treatment with methazolamide

Abstract

The retina contains Na+K+-ATPase and carbonic anhydrase (CA), enzymes that regulate ion fluxes across cell membranes of photoreceptors. Since inhibition of retinal Na+K+-ATPase by digitalis impairs colour vision, we wanted to find out whether this also occurs after inhibition of CA. In a double-masked crossover study with placebo, 14 male volunteers were given 50 mg q.i.d. of the CA inhibitor methazolamide for 2 weeks. 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 degree of acidosis or to other side-effects. Its mechanism could be interpreted as a specific effect of CA inhibition in the retina (or the visual cortex) calculated to more than 99.9%. © 1995 Royal College of Ophthalmologists.