Differential diagnosis of typical and atypical congenital achromatopsia. Analysis of a progressive foveal dystrophy and a nonprogressive oligo-cone trichromasy (general cone dysfunction without achromatopsia), both of which at first had been diagnosed as achromatopsia.

Report on two patients whose symptoms suggested the presence of congenital achromatopsia. In one case there was indeed total colour blindness, but a normal photopic ERG. Here, achromatopsia is the present stage in a process of slow functional decay of the central retina. Most probably the underlying disorder is progressive foveal dystrophy, a central form of cone dystrophy. In the other case there was a nonrecordable photopic ERG, but trichromatic colour vision. This appears to be another patient with oligo-cone trichromasy (general cone dysfunction without achromatopsia), as described by Van Lith.