Visual field and electrophysiological abnormalities due to vigabatrin.

The purpose of this study was to determine the electrophysiological changes in patients using the anti epileptic drug vigabatrin and to correlate these findings with the previously reported risk for visual field loss in these patients. In 1998 the neurologists of both involved hospitals referred all patients on vigabatrin medication for ophthalmological examination to the outpatients clinics. Of the 33 patients whom were referred to our outpatient clinics, four had to be dropped from the study because of disability to perform the examinations the remaining 29 patients were included in the study. Standard ophthalmological investigations were carried out, and contrast sensitivity, visual field (Humphrey 30-2 and Esterman or Octopus 32), colour vision (panel D15), ERG and EOG according to ISCEV standards were tested. 18 patients continued the medication and 11 stopped taking the drug during the study. Nine of the patients who stopped the drug were followed during at least half a year afterwards, this group will be described in the combined article 'Electro ophthalmic recovery after withdrawal from vigabatrin' (Graniewski and Van der Torren, this issue). The electro-ophthalmological findings in the group of 29 patients were correlated with the visual fields and the daily and cumulative dosages of vigabatrin. Of the patients, 32% showed no visual field constriction at all; from these patients 64% had EOG and/or ERG changes. Of the patients with slight to marked visual field constriction, 90% presented EOG and/or ERG changes. Significant correlation between daily dosages of vigabatrin and visual field defects was shown as well as between visual field defects and rod and cone b wave amplitude reductions. Cumulative vigabatrin dosages presented a significant correlation with EOG ratio and ERG rod b-wave amplitude. Conclusively EOG and ERG testing were found to be even an more accurate way to monitor the direct vigabatrin effect on the outer retina and is possible different from the visual field testing.

Electro-ophthalmological recovery after withdrawal from vigabatrin.

UNLABELLED: This study describes the effects of stopping of the anti-epileptic drug vigabatrin on the visual field and electrophysiological changes in one third of the group of patients which is described in the paper 'Visual field and electrophysiological abnormalities due to vigabatrin' (Van der Torren and Graniewski, 2002). In 1997 several reports described the possible oculotoxic effect of vigabatrin followed by a reconsideration of this medication in epileptic patients. Vigabatrin was discontinued in one-third of the patients on chronic medication (mean duration 4.8 years). The visual field and electrophysiological examinations were repeated every 3 months if possible, otherwise at 6-month intervals. The EOG Arden index and the ERG rod b-wave showed a significant improvement when vigabatrin was discontinued. Repeated examinations of visual fields and electrophysiology shortly after discontinuation of the drug (between 1 and 3 months) and later on after 6 months and 1 year showed a recovery of the EOG Arden index and the ERG rod b-wave during this period. The visual fields did not change in either direction. CONCLUSION: the recovery effect is a strong argument for the hypothesis that the reduction in EOG and ERG b-wave is an oculotoxic effect. The electrophysiological improvement during 6 months or longer after discontinuation and the unchanged visual fields are an argument for the hypothesis that the visual field represents the irreversible intoxicating effect on the retina, whereas the electrophysiology represents a more direct effect on the retinal glial cells level.