The Electroretinogram of a Cone-Monochromat

In subjects with monochromatic vision the absence of color discrimination is due most often to a generalized cone dysfunction, visual perception depending almost exclusively on the scotopic (rod) mechanism.1,2As a result, the rod-monochromat has markedly reduced visual acuity and exhibits an aversion to bright lights. However, another form of total color-blindness has been described in which visual acuity is normal and symptoms relating to photopic luminances are absent.3,4The most extensive study of this rare type, known as cone-monochromatism, has been reported by Weale,4,5and it is a further examination of one of his subjects that forms the topic of this communication. Although the etiology of cone-monochromatism is obscure previous experimental results for our subject suggest that the defect is postreceptoral. For example, Weale5has demonstrated, by means of fundus reflectometry, that the two photosensitive cone pigments detectable in the normal fovea are present also