Vigabatrin is used to treat epilepsy and can lead to increased levels of gamma-aminobutyric acid (GABA) in the brain and in the retina leading to binasal visual field defects. Although not the first line of treatment for adults it is still used in epileptic children. Monitoring visual fields accurately is challenging in children hence the need for alternative testing. The study team evaluated the visual fields from adult patients attending routine clinic follow-up for vigabatrin medication. Twelve patients with suspected vigabatrin attributed visual field defects were selected for the study. They were re-examined with computerised kinetic perimetry, ff-electroretinogram (ERG) and optical coherence tomography (OCT) (2D circle scan). All patients demonstrated constricted visual fields. Comparative analysis of ff-ERG parameters showed reduced b-wave amplitudes for the isolated and the combined rod and cone responses (P<0.0001). The a-wave, reflecting photoreceptor activity, was reduced (P=0.001), as well as the summed amplitude of oscillatory potentials (P=0.029), corresponding to inner retinal function. OCT measurements demonstrated attenuation of the retinal nerve fibre layer (RNFL) in nine of 12 patients, most frequently superiorly and / or inferiorly. No temporal attenuation was found. Significant positive correlations were found between the total averaged RNFL thickness, superior and inferior RNFL thickness and reduced ff-ERG parameters. Positive correlations were also found between RNFL thickness and isopter areas. The results are encouraging and OCT measurement of the RNFL thickness may be of clinical value in monitoring patients especially children on vigabatrin therapy.

Attenuation of the retinal nerve fibre layer and reduced retinal function assessed by optical coherence tomography and full-field electroretinography in patients exposed to vigabatrin medication.
Kjellstrom U, Andreasson S, Ponjavic V.
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Nana Theodorou

BMedSCi (Hons) PhD, Sheffield Teaching Hospitals NHS Foundation Trust, Clinical Research Office, 11 Broomfield Road, Sheffield, S10 2SE, UK.

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