Abstracts

This study was designed to differentiate between retinal dysfunction associated with vigabatrin (VGB) therapy and non-specific visual field defects in people with treated epilepsy., A total of 204 people with epilepsy were grouped according to antiepileptic drug therapy as follows: current VGB treatment (n=56), previous VGB treatment (n=49), current GABAergic treatment (no VGB exposure; n=46) and current non-GABAergic treatment (no VGB exposure; n=53). Groups were matched for age, sex, seizure-type, and seizure frequency. All patients underwent wide-field multifocal electroretinography (WF-mfERG)¹, logMar visual acuity testing, colour vision assessment, static perimetry (Humphrey) and ISCEV standard electroretinography., When assessed by static perimetry, bilateral visual field constriction was observed in 33 current-VGB patients (59%) and 21 of the previous VGB group (43%). However, clinically significant abnormalities were also demonstrated in 24 patients (24%) with no prior exposure to VGB. Assessment of retinal function by WF-mfERG revealed abnormal responses in 25 current VGB patients (48%) and 11 previous-VGB patients (22%), but none (0%) of the patients with no exposure to VGB. By way of comparison, 21 VGB-exposed patients (20%) demonstrated visual field abnormalities with no associated retinal dysfunction, whereas only 3 patients (3%) had demonstrable retinal dysfunction with no apparent visual field problems. Unlike with visual field abnormalities, the incidence of retinal dysfunction segregated according to median VGB drug load (dysfunction, n = 31, 9012g versus no dysfunction, n = 40, 5065g; p=0.0035). There was no difference between groups in terms of visual acuity, colour vision and standard electroretinography assessments., Visual field abnormalities are common in the treated epilepsy population, irrespective of drug history. Bilateral concentric visual field constriction may be a surrogate clinical marker of the neuroretinal toxicity associated with VGB use, but its assessment by conventional static perimetry is neither sufficiently sensitive nor specific to reliably identify all affected individuals. Patients with current or previous exposure to VGB should be considered for WF-mfERG, which is more likely to reflect retinal toxicity associated with vigabatrin usage., (Supported by a research grant from the Chief Scientist Office, Scotland.)