Electroretinographic Oscillatory Potentials and Flicker Responses in Pediatric Patients Taking Vigabatrin

Abstract

Purpose: The cumulative dose of the antiepileptic drug vigabatrin (VGB) has been associated with visual field (VF) loss. In patients unable to do conventional VF tests due to immaturity or disability, surveillance for adverse effects of VGB is done using electroretinography (ERG). In this study, we evaluated the ERG oscillatory potentials (OPs) and responses to flickering stimuli for significant differences between VGB users and controls, as well as significant correlation with dose or duration of VGB use.

Methods: Extant ERG records from VGB users (n=64) were compared to those of healthy controls. The records included responses of the dark-adapted eye to a range of brief, full-field blue flashes (0.06-20 cd s/m²) of doubling intensity, and cone-isolated responses to red flashes (0.28-35 cd s/m²) presented on a steady white background (25.5 cd/m²). The amplitude and implicit time of individual OPs, demonstrated by passing the records through a 5^th order Butterworth filter (bandpass 70-300 Hz), were measured, and the energy of the OPs was calculated from the area under the Fourier-transformed record. Responses to flickering white stimuli (2.25 cd s/m² with a 25.5 cd/m² background; 10, 25, 31.25 Hz ) were obtained; the amplitude and phase of the first four harmonics in these responses were processed. Respective ANOVA were used to detect differences in rod and cone OPs (intensity×OP×group) and flicker (frequency×harmonic×group) parameters. ERG data were also evaluated for significant relation to dose and to duration of VGB using Pearson’s product moment.

Results: In VGB users, both rod and cone OP amplitudes and flicker responses to the two higher frequencies were significantly attenuated. In spite of this, neither OP energy nor the amplitude of the fundamental at any of the three frequencies tested was significantly related to VGB dose or duration of use. However, consistent with Westall et al. (Doc Ophthalmol, 2002), inspection of the OP energy vs. duration on VGB data suggests a possible quadratic relationship (i.e. rising and falling).

Conclusions: Although VGB use is associated with attenuated ERG responses, these data do not show a relationship to VGB dose or duration. In view of these results, continued effort to develop procedures for evaluation of the peripheral VF in VGB users is warranted.

Keywords: 509 electroretinography: clinical • 503 drug toxicity/drug effects • 758 visual fields