Vigabatrin visual toxicity: Evolution and dose dependence

Purpose: To investigate the prevalence and prognosis of visual field defect s (VFDs) in epilepsy patients with and without vigabatrin (VGB) treatment, to investigate the possible relationship between VFDs and cumulative VGB do se, and to characterise the evolution of VFDs. Methods: A cohort of 155 presurgical candidates who had undergone full-fiel d Goldmann perimetry (GP) was studied, 99 (64%) of whom had been treated wi th VGB. All GPs were reevaluated in 1998 by one experienced examiner, blind ed to medication. Duration of treatment and total VGB dose were related to perimetric results. Results: Twenty-five (16%) of the 155 patients had VFDs: Nineteen (19%) of the 99 VGB-treated patients, and six (11%) of the 56 patients unexposed to VGB. VGB-treated patients with VFDs had been treated significantly longer t han those without VFDs. Cumulative VGB dose could be calculated for 84 pati ents. The prevalence of VFDs increased significantly with increasing total VGB-dose, from 4% in the 51 patients who had been exposed to less than or e qual to1 kg VGB, to 75% in the eight patients with a total dose of 3-5 kg o f VGB. Sixteen VGB-treated patients were reexamined 2-10 years later. In th e 12 where evaluation was possible, all still had VFDs, which had worsened in five cases (42%) and improved in none. Conclusions: This study indicates a strong relationship between VFDs and du ration and total dose of VGB. VFDs were irreversible and in a substantial p ercentage progressive. Similar VFDs may, however, also be found in patients unexposed to VGB. A model of the evolution of the VFDs in VGB toxicity is introduced, and a new simple visual field test is proposed.