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S. Parks, J. McDonagh, F. Dolan, G.N. Dutton, D. Keating, M.J. Brodie; Separating the Transient Physiological Effects and Retino-Toxic Effects of Vigabatrin Related Retinal Dysfunction Using the Wide Field Multifocal ERG . Invest. Ophthalmol. Vis. Sci. 2003;44(13):2721.
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Purpose: Studies have reported bilateral visual field defects and electrophysiological abnormalities in vigabatrin-treated patients. We employed a novel investigation, the wide-field multifocal electroretinogram (WF-mfERG), to objectively map retinal function in such patients and determine the best parameter that correlated with visual field abnormalities. Methods: Thirty-two adults who had taken vigabatrin for at least three years for localisation-related epilepsy underwent WF-mfERG, electroretinography (ERG), LogMar visual acuity and colour vision evaluation, Humphrey visual field analysis and funduscopy. The group was matched for age, sex and seizure type with a cohort of control patients who had never received vigabatrin but were currently taking alternative anti-epileptics. Results were compared with a normative data set with respect to potential bilateral abnormalities in response timing. Results: There were no significant differences between groups in visual acuity or colour vision testing. Of the vigabatrin patients, 19 (59%) had bilateral visual field defects compared to none of the controls. ERG and WF-mfERG abnormalities were found in both groups. However, only ERG (cone, flicker) and the difference between peripheral-central implicit time of the WF-mfERG significantly correlated with visual field defects. WF-mfERG implicit time analysis provided (100% sensitivity) and only two of the 13 patients without a field defect displayed implicit time abnormalities (86% specificity). Conclusions: The study adds weight to evidence that suggests that there is a transient physiological effect produced by the anti-epileptics not specific to visual field loss or vigabatrin (14 vigabatrin and 6 control patients had at least one abnormal ERG response). However, abnormalities in WF-mfERG implicit time, 30Hz flicker and cone response were specific to patients with vigabatrin related visual field defects. As with previous studies, responses reflecting predominately cone pathway activity appear to be significantly related to visual field abnormalities. Although WF-mfERG was the most sensitive indicator, these results indicate that the central mfERG responses although abnormal, are not sufficiently sensitive to predict field loss. This would indicate that the standard mfERG (i.e <60° field stimulation) is unlikely to yield sufficient sensitivity to improve on the accuracy or simplicity of the flicker ERG.
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