Rod and cone receptor mechanisms in typical and atypical congenital achromatopsia

Abstract Spectral sensitivities and interactions of the receptor systems of thirteen congenital achromats with reduced acuity were determined by psychophysical measurements with white and blue light. Patients were of three categories: (1) rod monochromats: functioning rods only. (2) blue monocone monochromats: blue sensitive cones (maximum at 440 mμ) and foveal rods with normal scotopic curve modified by the absorption of macular xanthophyll; these patients function as blue cone monochromats at high luminances, as rod monochromats at low luminances, and as blue cone-rod dichromats at intermediate luminances. (3) intermediates, with rods and blue cones of insufficient number for color discrimination. All patients are believed to have the same receptor systems. Differences in fixation seem to explain the functional differences.