Value of the ERG in congenital nystagmus.

A group of 64 children with poor vision and early onset nystagmus were investigated retrospectively by the electroretinogram (ERG). Fifty-eight of these children also underwent analysis of the visual evoked potential (VEP), and 40 underwent colour vision analysis. Seventeen children were found to have complete congenital achromatopsia (rod monochromatism), being identified by their total colour blindness, reduced visual acuity, and reduced or absent photopic and flicker (30 Hz) ERGs. Two children with incomplete X-linked congenital achromatopsia were also found. This study identified the need to investigate children with nystagmus by means of the ERG and suggested that the ERG was useful where the diagnosis was uncertain, particularly at early school age. The incidence of congenital achromatopsia in a group of otherwise undiagnosed children with early onset nystagmus was high (29%), with 40% being classified as having congenital idiopathic nystagmus.