Examining visual field defects in the paediatric population exposed to vigabatrin

The antiepileptic drug, vigabatrin, has been linked to a specific pattern of visual field loss. The majority of studies have not included the paediatric population due to difficulties assessing visual field function. This is a particular problem as vigabatrin is effective against infantile spasms. A field-specific visual evoked potential was developed which consisted of a central stimulus (0-5 degrees radius) and a peripheral stimulus (30-60 degrees radius). Both stimuli consist of black and white checks which increase in size with eccentricity. Responses are recorded from occipital electrodes O2 and O1 referred to frontal electrode Fz. Electroretinograms and perimetry was performed were possible as a comparison. Thirty-nine children with epilepsy treated with vigabatrin aged from 3 to 15 years were included in the study; 35/39 children complied with the field-specific VEP, 26/39 complied with the ERG and 11/39 performed perimetry. Of these results, 18 children had normal ERG responses and eight had abnormal response. Visual field testing revealed four children had abnormal and seven had abnormal visual field results. The Field-specific VEP identified three of four abnormal perimetry results and six of seven normal perimetry results, giving a sensitivity of 75% and a specificity of 85.7%. When comparing perimetry results with the ERG parameters only the 30-Hz flicker amplitude, with a cut-off amplitude below 70 microV, gave a useful sensitivity of 75% and a specificity of 71%. The field-specific VEP is a useful alternative method that is both well tolerated by young children and gives a reliable indication of likely peripheral visual field loss associated with vigabatrin. The defect appears to have a similar prevalence in children as it does in adults.