A visual-evoked potential (VEP) technique for identifying visual field defects in children with epilepsy treated with vigabatrin has been developed at Aston University, Birmingham, and Cardiff University, UK. The VEP was field specific with a central (0-5 degree radius) and peripheral stimulus (30-60 degree radius). Black and white checks used as stimuli increased in size with eccentricity and reversed at different rates, allowing a record of separate central and peripheral responses. Initially, five vigabatrin-treated young adults with field defects were identified using this technique and were examined with electroretinograms (ERG). Of 39 children aged 3 to 15 years treated with vigabatrin, 35 complied with the field-specific stimulus, 26 complied with ERG, and 12 with perimetry. The field-specific stimulus identified 3 of 4 abnormal and 7 of 8 normal perimetry results, with good sensitivity (75%) and specificity (87.5%). A typical vigabatrin visual field loss occurred in 25.7% of children treated, similar to the prevalence in adults. Combined with the ERG 30-Hz flicker amplitude, the field specific stimulus is a satifactory method for identifying VGB-induced visual field loss in children older than 2 and under 10 years of age. [1]

COMMENT. The specific vigabatrin-induced visual field loss is a bilateral concentric constriction with binasal annular defect and relative temporal sparing. Central vision is usually unaffected by vigabatrin. Vigabatrin is sometimes advocated in the treatment of West syndrome, a condition with onset in infancy. Since the test described for detecting visual field defects was applied to children between 3 and 15 years, presumably it would not be appropriate for the majority of infants treated. The 25% risk of visual field loss is of serious concern in the continued use of vigabatrin for infantile spasms, despite the ability to identify the defect in younger children.