Sills GJ, Patsalos PN, Butler E, et al. Visual field constriction. Accumulation of vigabatrin but not tiagabine in the retina.

Sills GJ, Patsalos PN, Butler E, et al. Visual field constriction. Accumulation of vigabatrin but not tiagabine in the retina. Neurology 2001;57:196–200. The anticonvulsant vigabatrin is reported to constrict the visual field in 40% of treated adults 65% of treated children. The drug increases the concentrations of the inhibitory neurotransmitter gamma-aminobutyric acid (GABA). The mechanism of visual field constriction is not clear. Tiagabine, another new anticonvulsant, has also been reported to cause visual field defects. It may also increase GABA by inhibiting GABA reuptake. In this study, the authors measured GABA concentrations in the brain retina in adult male rats after administration of vigabatrin or tiagabine. Vigabatrin accumulated in the retina caused accumulation of GABA in the retina at 5-fold the amount in the brain. Tiagabine did not accumulate in the retina or affect GABA concentrations there. The authors concluded that vigabatrin accumulation perhaps an increase in GABA concentration may be responsible for the visual field constriction. Tiagabine was considered unlikely to cause visual field defects in humans.