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, EOG, 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. EOG, a more sensitive diagnostic tool than ERG for screening vigabatrin-treated patients, also appears to be more specific.