Japanese family with blue cone monochromatism.

The diagnosis of blue cone monochromatism (BCM) is based on severely affected color vision with preserved blue function, nearly nonrecordable photopic ERG, and a family pedigree compatible with X-linked inheritance. We have studied the color vision and ocular function of three members of a family with BCM and a female carrier in the same family. Two of the three affected family members, 9- and 7-year-old brothers, showed the unique features of BCM in their color vision and ERG. The third affected family member, a 43-year-old uncle, showed achromatic vision. He had diabetic retinopathy and moderate cataract which were thought to disturb his blue cone function, causing apparent rod monochromatism. The female carrier, the mother of the brothers, showed normal visual functions except for a slight reduction in photopic ERG amplitude. We believe that this is the first description of BCM in a Japanese family.