Changes in color vision after a single dose of vigabatrin or carbamazepine in healthy volunteers

In patients with epilepsy the older antiepileptic drugs induce distinct electroencephalographic changes and may also alter visual function. Although the effects of the newer antiepileptic drugs on the electroencephalogram remain less clear, long-term treatment with vigabatrin (VGB) has been reported to induce severe and permanent visual impairment. Our aim in this study was to investigate the effects of a single oral dose of VGB and carbamazepine (CBZ) on visual function in normal healthy volunteers randomly assigned to three groups according to a single-blind, placebo-controlled design. All subjects underwent color visual evoked potential tests and color perimetry at baseline and after receiving placebo, VGB (2,000 mg) or CBZ (400 mg). Whereas CBZ induced a mild overall impairment of the chromatic and achromatic systems, VGB induced a selective blue impairment. The differential changes the two antiepileptic drugs induced in visual tests presumably depend on their different mechanisms of action. The selective blue impairment in color visual tests in VGB-treated healthy subjects is consistent with gamma-aminobutyric acid (GABA)-ergic inhibition also at retinal level. Hence, color visual tests may be suitable to detect initial visual abnormalities in VGB-treated patients with epilepsy.