Separating the retinal electrophysiologic effects of vigabatrin Treatment versus field loss

Objective: To separate the retinal electrophysiologic markers associated with vigabatrin-attributed visual field loss (VGB-VFL) from those associated with current vigabatrin therapy. Methods: A nonrandomly selected cohort of 8 previous and 18 current vigabatrin users and a reference cohort of 8 never vigabatrin-treated patients with epilepsy receiving other antiepilepsy drugs (AED) underwent electro-oculography (EOG), electroretinography (ERG), and automated static threshold perimetry. A cohort of 22 normal subjects underwent ERG. The validity of the retinal electrophysiologic variables to detect the presence and severity of VGB-VFL was assessed using receiver operator characteristic curves. Results: Of 26 patients exposed to vigabatrin, 18 exhibited VGB-VFL. No patients receiving alternative AED showed this type of visual field abnormality. The presence and severity of VGB-VFL was significantly associated with the latency (implicit time) and amplitude of the ERG cone function. The amplitude of the cone flicker response was the strongest predictor of VGB-VFL and revealed a sensitivity of 100% at a specificity of 75%. The EOG, the photopic and scotopic ERG, and the latency of the ERG second oscillatory potential (OP2) were not significantly related to the presence of VGB-VFL. Vigabatrin therapy was significantly associated with the photopic amplitude, the scotopic a-wave latency, and the latency of OP2. Conclusion: In patients who cannot perform reliable perimetry, the cone-specific ERG flicker amplitude provides the best screening method for detecting VGB-VFL.