Characteristics of a unique visual field defect attributed to vigabatrin

Vigabatrin (VGB) therapy is associated with a loss of peripheral vision. The characteristics and prevalence of VGB-attributed visual field loss (V-AVFL) and associated risk factors were evaluated in patients with epilepsy.

The material comprised the visual fields and case notes of 88 patients with suspected V-AVFL (25 spontaneous reports and 63 cases from an open-label extension trial) and of 42 patients receiving alternative antiepileptic drugs (AEDs) from a cross-sectional study.

Forty-two reliable cases of visual field loss could not be assigned to an alternative known cause and were therefore attributed to VGB (13 spontaneous reports and 29 from the open-label study). All cases except one were asymptomatic. Seven cases of field loss were present in the reference cohort of 42 patients; all cases could be attributed to a known aetiology. Thirty-six of the 42 confirmed cases of V-AVFL exhibited a bilateral defect that was most profound nasally, and three, a concentric constriction. The prevalence of V-AVFL was 29% (95% confidence interval, 21-39%). Male gender was associated with a 2.1-fold increased relative risk of V-AVFL (95% confidence interval, 1.20-4.6%). Age, body weight, duration of epilepsy, and daily dose of VGB, and concomitant AEDs did not predict the occurrence of V-AVFL.

The unique visual field defect attributed to VGB is profound in terms of the frequency of occurrence and the location and severity of loss. The asymptomatic nature of the field loss indicates that V-AVFL can be elicited only by visual field examination.