Outer retinal dysfunction in patients treated with vigabatrin

Objective: To assess early visual impairment related to vigabatrin prospectively in patients with and without visual symptoms. Background: Vigabatrin acts as an inhibitor of gamma-aminobutyric acid (GABA) transaminase. GABA-induced ion transport changes in the retinal pigment epithelium have been described. The electro-oculogram (EOG) is a clinical test that reflects photoreceptor and pigment epithelium function. Patients and methods: Of the 22 consecutive patients presenting with a history of partial seizures currently treated with vigabatrin, 20 were included in the study. A complete clinical ophthalmologic and neurologic examination was performed, including static 100-point perimetry, EGG, and electroretinogram (ERG). Results: In 14 of 20 patients, the light/dark ratio (Arden ratio) of the standard EOG was reduced in at least one eye. The a- and b-wave amplitudes and implicit time of the ERG were within the normal range in all patients; however, ERG oscillatory potentials could not be recorded in 10 patients. Twelve patients had visual field constriction; five complained of visual symptoms. The most severe visual impairment was observed in patients treated with both vigabatrin and valproate. Conclusions: There is some evidence of outer retinal dysfunction in the patients treated with vigabatrin. EGG, a more sensitive diagnostic tool than ERG for screening vigabatrin-treated patients, also appears to be more specific.