Vigabatrin: longterm follow-up of electrophysiology and visual field examinations

Background: To report the results of repeated electrophysiological and visual field examinations in patients with vigabatrin-associated visual field loss (VGB-VFL) and the relationship between these electrophysiological findings, the cumulative dose of vigabatrin and the extent of visual field loss. Methods: Twenty-two eyes of 11 patients with VGB-VFL were studied. All patients underwent surgery for therapy-resistant epilepsy. Repeated electrooculograms (EOGs) and flash electroretinograms (ERGs) were made and the cumulative dose of vigabatrin and the visual field loss were recorded after a period of 37 - 47 months. Results: The visual field loss was stable in patients who had stopped vigabatrin at the time of the first examination. There was a slight increase in VFL in patients who continued vigabatrin. During the second EOG and ERG, abnormalities in scotopic and photopic a-wave latencies and in scotopic b-wave amplitude were found in more than 50% of patients. Only b-wave latency became normal, while EOG, a-wave latency, a-wave amplitude and b-wave amplitude stayed abnormal. The amount of VFL and the cumulative dose of vigabatrin were statistically correlated with the b-wave amplitude, mainly photopic, found during the first and second examinations. Conclusion: After 4 years, EOG, flash ERG and visual field loss had not improved in patients with VGB-VFL. The statistically significant correlation found during the first examination between the amount of VFL and the cumulative dose of vigabatrin with the ( mainly photopic) b-wave amplitude remained constant.