Vigabatrin: longterm follow‐up of electrophysiology and visual field examinations

Abstract

ABSTRACT.Background: To report the results of repeated electrophysiological and visual field examinations in patients with vigabatrin-associated visual field loss (VGB-VFL) and the relationship between these electrophysiological findings, the cumulative dose of vigabatrin and the extent of visual field loss. Methods: Twenty-two eyes of 11 patients with VGB-VFL were studied. All patients underwent surgery for therapy-resistant epilepsy. Repeated electrooculograms (EOGs) and flash electroretinograms (ERGs) were made and the cumulative dose of vigabatrin and the visual field loss were recorded after a period of 37-47 months. Results: The visual field loss was stable in patients who had stopped vigabatrin at the time of the first examination. There was a slight increase in VFL in patients who continued vigabatrin. During the second EOG and ERG, abnormalities in scotopic and photopic a-wave latencies and in scotopic b-wave amplitude were found in more than 50% of patients. Only b-wave latency became normal, while EOG, a-wave latency, a-wave amplitude and b-wave amplitude stayed abnormal. The amount of VFL and the cumulative dose of vigabatrin were statistically correlated with the b-wave amplitude, mainly photopic, found during the first and second examinations. Conclusion: After 4 years, EOG, flash ERG and visual field loss had not improved in patients with VGB-VFL. The statistically significant correlation found during the first examination between the amount of VFL and the cumulative dose of vigabatrin with the (mainly photopic) b-wave amplitude remained constant.

Retinal Function in Rabbits Does Not Improve 4–5 Months after Terminating Treatment with Vigabatrin

“…Similar reductions in cone b-wave amplitudes in the 30 Hz flicker ERG are also seen in rabbits receiving vigabatrin [14]. Several studies have demonstrated a reduced ERG also after discontinuation of medication [15,17,18,21]. Duboc et al [27] have performed a study in rats, tissue has been confirmed in another investigation by Sills et al [29].…”

“…Most of these studies have demonstrated neither improvement nor worsening 1-47 months after treatment was stopped, suggesting that the visual field defect is irreversible but not progressive [15][16][17][18][19][20][21]. In addition, some of these investigators have assessed ERGs, which showed irreversible changes [15,17,18,21]. The most consistent ERG results were a reduction in photoptic b-wave amplitude, a reduction in amplitudes of the oscillatory potentials and a reduction in amplitudes of the 30 Hz flicker ERG.…”

Full-field ERG and visual fields in patients 5 years after discontinuing vigabatrin therapy

“…Quite a few studies have addressed the question whether these defects are reversible or not and most data support the hypothesis of permanent visual field constriction [12,14,15,[17][18][19][20][21][22]. The time of follow-up varies between the different studies spreading from 3 to 38 months.…”

Dose-related changes in retinal function and PKC-alpha expression in rabbits on vigabatrin medication

“…VGB medication has been correlated to a reduction of rod b-wave amplitudes and cone b-wave amplitudes, as well as to a decline of amplitudes of oscillatory potentials (OPs), reflecting inner retinal function. The ff-ERG alterations are usually considered irreversible [19,22,23,25]. To date, there have been uncertainties concerning the role of the drug dose in VGB toxicity.…”

“…The cause of the visual field defects is still not fully understood. Numerous studies have revealed alterations of full-field ERG (ff-ERG) responses [11,13,16,[18][19][20][21][22][23][24][25][26][27][28], suggesting retinal damage as the origin of visual field defects. VGB medication has been correlated to a reduction of rod b-wave amplitudes and cone b-wave amplitudes, as well as to a decline of amplitudes of oscillatory potentials (OPs), reflecting inner retinal function.…”