Characteristics of a Unique Visual Field Defect Attributed to Vigabatrin

Abstract

Summary:Purpose: Vigabatrin (VGB) therapy is associated with a loss of peripheral vision. The characteristics and prevalence of VGB-attributed visual field loss (V-AVFL) and associated risk factors were evaluated in patients with epilepsy.Methods: The material comprised the visual fields and case notes of 88 patients with suspected V-AVFL (25 spontaneous reports and 63 cases from an open-label extension trial) and of 42 patients receiving alternative antiepileptic drugs (AEDs) from a cross-sectional study.Results: Forty-two reliable cases of visual field loss could not be assigned to an alternative known cause and were therefore attributed to VGB (13 spontaneous reports and 29 from the open-label study). All cases except one were asymptomatic. Seven cases of field loss were present in the reference cohort of 42 patients; all cases could be attributed to a known aetiology.Thirty-six of the 42 confirmed cases of V-AVFL exhibited a bilateral defect that was most profound nasally, and three, a concentric constriction. The prevalence of V-AVFL was 29% (95% confidence interval, 21-39%). Male gender was associated with a 2.1-fold increased relative risk of V-AVFL (95% confidence interval, 1.2046%). Age, body weight, duration of epilepsy, and daily dose of VGB, and concomitant AEDs did not predict the occurrence of V-AVFL.Conclusions: The unique visual field defect attributed to VGB is profound in terms of the frequency of occurrence and the location and severity of loss. The asymptomatic nature of the field loss indicates that V-AVFL can be elicited only by visual field examination. Key Words: Vigabatrin-Visual field-Prevalence-Bilateral nasal annular field loss-Risk factors.Vigabatrin (VGB) is an effective and well-tolerated drug used for the treatment of partial seizures in adults and children. The drug resembles y-aminobutyric acid (GABA), which is a major inhibitory neurotransmitter present in the retina and brain. The anticonvulsant effect is achieved by irreversible inhibition of the enzyme GABA-transaminase, which catalyses the inactivation of GABA.An increasing number of spontaneous reports suggest an association between VGB and visual field loss (1-12). These reports, although convincing, are based on limited numbers of patients, and a number of fundamental issues remain unclear. The form of the visual field loss including the severity and location of the defect, has received little attention. Knowledge of these characteristics is esAccepted July 15, 1999. sential if an effective screening procedure is to be provided and if the risk-benefit ratio in treated patients is to be evaluated correctly. The excess risk of VGBattributed visual field loss (V-AVFL) is unknown and can be estimated only by undertaking visual field examinations in a cohort of patients treated with VGB and in a reference cohort receiving alternative antiepileptic drugs (AEDs). The risk factors for V-AVFL also are unknown and require knowledge of the prevalence of the individual characteristics in each of the cohorts. Spontaneous reports and ...

Retinal nerve fibre layer characteristics with vigabatrin-associated visual field loss—could scanning laser polarimetry aid diagnosis?

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