Vigabatrin-associated loss of vision: Rarebit perimetry illuminates the dose-damage relationship

Abstract

Purpose: The utility of vigabatrin in the treatment of epilepsy is partially offset by its retinal toxicity. The relationship between dosage and damage is obscure. This may be due to perimetric shortcomings. The new technique of rarebit ('microdot') perimetry might be more informative. Methods: Twelve patients who had been treated with vigabatrin for various durations were examined by manual, kinetic perimetry and by rarebit perimetry. Results: Rarebit results differed significantly between patients and normal controls and rarebit deficits were directly proportional to cumulated vigabatrin doses (correlation coefficients were -0.92 in the nasal field and -0.82 in the temporal field). Manual perimetry results were less clearly related to dosage (r = -0.54 and r = -0.73, respectively). Conclusion: Rarebit perimetry indicates that each treated subject will develop visual loss and that visual loss will be proportional to the accumulated dose. Conventional perimetry is less well suited to detecting and quantifying vigabatrin-associated visual loss.