Color discrimination ability of 53 patients with
congestive heart failure and 32 healthy volunteers treated with
digoxin,
digitoxin, or
pengitoxin was determined with the Farnworth's Munsell 100 hue test. The patients had been treated with
digitalis glycosides for several months prior to color vision testing. The volunteers received
glycosides until a steady-state plasma concentration was reached.
Glycoside plasma levels were measured by radioimmunoassay on the 3 days prior to color vision testing. The total error scores, indices of color discrimination, increased with the
glycoside plasma levels. Subjects treated with
digitoxin or
pengitoxin exhibited no marked elevation in total error score at therapeutic concentrations, whereas 17 of 28 subjects with therapeutic
digoxin plasma concentrations (less than 2.0 ng/ml) showed disturbed color discrimination. At toxic plasma levels all 5
digoxin-treated subjects, 7 of 13
digitoxin-treated subjects, and 3 of 8
pengitoxin-treated subjects showed impairment of color discrimination. The greater tendency of
digoxin to impair color vision in comparison with
digitoxin and
pengitoxin may be related to a higher uptake or different distribution in the retina.