Dissociated vertical deviation: evidence of abnormal visual pathway projection.

Abnormalities in visually evoked responses have been used to demonstrate abnormal optic nerve fibre projections in human albinos, who have anomalous nystagmoid movements. Using visually evoked potentials we tested the hypothesis that patients with dissociated vertical deviation (another group with anomalous nystagmoid movements) may have abnormal visual evoked responses similar to those of albinos. Patients with dissociated vertical deviation (both unilateral and alternating), patients with congenital esotropia without dissociated vertical deviation, and normal subjects were investigated. The results showed a very high incidence of abnormal visual evoked responses in patients with dissociated vertical deviation, while recordings from the other groups were normal. As well as suggesting the possibility of abnormalities of optic nerve fibre projections, the visual evoked responses showed a marked increase in latency in all patients with dissociated vertical deviation. These results occurred regardless of the visual acuity or amblyopia of the eyes tested. The possible existence of abnormal pathway projection in the presence of dissociated vertical deviation is discussed.