Visual field constriction and electrophysiological changes associated with vigabatrin

We investigated functional, morphological and electrophysiological changes in patients under anti-epileptic therapy with vigabatrin (VGB), a GABA aminotransferase inhibitor.

20 epileptic patients treated with vigabatrin (age range 25-66 years) were enrolled in this study. The referrals were made by the treating neurologist, based on suspected or known visual field changes in these patients. Two patients had vigabatrin monotherapy, 18 patients were treated with vigabatrin in combination with other antiepileptic drugs. None of the patients reported visual complaints. Patients were examined with psychophysical tests including colour vision (Farnsworth D15), dark adaptation threshold, Goldmann visual fields and Tuebingen Automated Perimetry (90 degrees). A Ganzfeld ERG and an EOG following the ISCEV standard protocol were also obtained. Additionally, all patients were examined with the VERIS multifocal ERG including recordings of multifocal oscillatory potentials.

Visual acuity, anterior and posterior segments, colour vision and dark adaptation thresholds were normal in all patients. Of 20 patients, 18 presented visual field constriction. All patients with visual field defects revealed altered oscillatory potentials waveforms in the ERG, especially in those patients with marked visual field defects. Multifocal oscillatory potentials were also delayed in those patients. In some patients a delayed cone single flash response (6/20), a reduced mERG amplitude (12/20) and a reduced Arden ratio (9/20) were found.

The present data indicate an effect of vigabatrin on the inner retinal layers. Since abnormalities of the oscillatory potentials were seen in all patients with visual field defects a dysfunction of GABA-ergic retinal cell transmission might be assumed.