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J. L. Sienna, T. Wright, C. Westall; The Photopic Negative Response - Potential Biomarker of Non-Reversible Changes Due to Vigabatrin?. Invest. Ophthalmol. Vis. Sci. 2010;51(13):5582.
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To investigate electrophysiological changes induced by Vigabatrin (VGB) treatment. Specific aims: 1) To assess whether photopic negative response (PhNR) is affected by drug use and drug discontinuation, 2) To compare PhNR with changes observed in 30 Hz flicker amplitude.
Cross-sectional retrospective database review. Flicker amplitude (amp) and implicit times (IT) of electroretinogram (ERG) were collected from database of VGB treated patients at The Hospital for Sick Children. 38 tests were administered after diagnosis of seizure disorder but before starting VGB, 77 tests were administered on VGB and 34 tests after VGB was discontinued. Amp and IT of PhNR were scored for waves generated using a red flash (30 P td.s/m2) on blue background at the lowest trough after the b-wave. To isolate the effects of VGB treatment from other developmental changes, linear functions describing the expected ERG development from children with seizure were generated using data recorded pre-VGB treatment. All values are expressed as difference from the expected value at test age. Data were divided into pre-VGB, VGB <3 months, VGB >3 months and off VGB. Tukey tests for multiple comparison of means were performed.
PhNR exhibited a transient decrease in magnitude of response in the first 3 months of treatment but this did not achieve significance. There were significant increases in magnitude after 3 months (p=0.030), which persisted after discontinuation of VGB (p=0.040). There were no significant changes in 30 Hz flicker amplitude across groups. PhNR exhibits significantly less variation pre-VGB treatment than 30 Hz flicker response (p<0.01).
PhNR is affected by VGB after 3 months of treatment and the effect persists after discontinuation. Significantly less variation before VGB treatment may make PhNR a more sensitive biomarker of changes due to VGB than 30 Hz flicker.
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