The value of electrophysiology results in patients with epilepsy and vigabatrin associated visual field loss

Abstract

ABSTRACT.Purpose: To determine the value of electrophysiological findings in patients with temporal lobe epilepsy and to relate these findings to the amount of concentric contraction of the visual field and the use of vigabatrin. Methods: Electro-retinograms and electro-oculograms were done on 30 patients, operated for temporal lobe epilepsy. The patients were divided into three groups: (A) concentric contraction of the visual field associated with a history of vigabatrin medication (15 patients), (B) normal visual field with vigabatrin use (11 patients) and (C) normal visual field without vigabatrin medication (4 patients).Results: Electrophysiological abnormalities were found in 50% of the patients in group A. The Arden ratio of the EOG was lowered in 57%. Abnormalities in the ERG were found: b-wave implicit time photopic F was prolonged (50%), b-wave amplitudes scotopic B (53%), C (73%) and G (50%) and photopic H (50%) were diminished. The amount of visual field loss and the total dose of vigabatrin used, showed only slight correlation with the ERG and EOG. The use of vigabatrin during the ERG and EOG recording in group A, gave a higher b-wave amplitude scotopic G in 64% of cases. The a-wave implicit times scotopic G (73%) and photopic G (59%) and H (73%) were shortened in group B. Conclusion: EOG was abnormal in 57% in group A. ERG abnormalities could only be found in 50% of group A, mainly in the inner retina. Since also the total dose of vigabatrin and the amount of visual field loss did not really show a correlation with the electrophysiological findings and results of literature are not unanimous, electrophysiology does not appear at present to be a good method to detect patients with, or at risk of, vigabatrin associated visual field loss. Regularly performed visual field examination remains the cornerstone in screening.

Does vigabatrin treatment for infantile spasms cause visual field defects? An international multicentre study

“…Several theories have been proposed about the cause of vigabatrin-associated VFDs. 12 These include toxic reaction (treatment duration and cumulative dosage, 5 daily dose 13 ), idiosyncratic reaction, 14 polypharmacy, 15 pharmacogenetic difference, 14 elevated levels of retinal ornithine, 16 light exposure, taurine deficiency, 17 GABA accumulation in the retina, 18 dysfunction in GABA-innervated horizontal and amacrine cells in the inner plexiform layer of the retina, 10 and the infantile spasm itself. 19 Maximum daily dose was a single most reliable indicator of risk of VFDs in VBG-exposed patients in one study.…”

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

“…Electroretinograms were recorded after 15 min preadaptation (waiting room FL tubes). Further details have been described previously (Hardus et al 2001b). The examinations were performed by two technical assistants, alternately.…”

“…In a former study, we found abnormalities in the electro-oculogram (EOG) and electroretinogram (ERG) single flash, mainly in the b-wave, scotopic and photopic, in approximately 50% of subjects with VGB-VFL (Hardus et al 2001b). Decreased photopic b-wave amplitude was found with more extensive visual field loss.…”

The effect of GABA and the GABA-uptake-blocker NO-711 on the b-wave of the ERG and the responses of horizontal cells to light

“…In many studies of the effect of vigabatrin in patients there was a reduction of the b-wave in parts of the patients, but not in all [3,4,8,9,26,42,50]. In some instances, the rod b-wave was not statistically different from those of control subjects [8,53].…”

“…The multiple GABAergic influences on the generation of the b-wave may also explain why, during vigabatrin therapy, which can impair peripheral vision, there are no consistent changes of the b-wave [4,8,24,26], although the oscillatory potentials and the 30-Hz flicker amplitude of the ERG seem to correlate with visual field loss [4,23,24,25,42]. When given therapeutically, vigabatrin is taken up by amacrine cells and blocks their normal metabolism.…”