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Aparna Raghuram, Oyinkansola Kolawole, Ronald M. Hansen, Anne B. Fulton; Flicker Electroretinogram - Temporal Response Function In Children On Vigabatrin (VGB). Invest. Ophthalmol. Vis. Sci. 2012;53(14):5731.
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© ARVO (1962-2015); The Authors (2016-present)
To study retinal processes in pediatric VGB patients, a novel approach with the flicker electroretinogram (ERG) was used. VGB is an anti-epileptic medication. Altered retinal processes, which are thought to be the basis for VGB induced irreversible visual field loss, remain incompletely understood.
ERG responses were recorded from 19 children on VGB. Their median age was 2.5 (range: 1.2 to 21.7) years and the median duration of VGB treatment was 13 (range: 3 to 69) months. Data were also collected from six adult control subjects. ERG responses to brief (<3ms) flashes modulated at 6 frequencies (10 Hz - 83 Hz) were recorded. The ERG response to a stimulus of zero contrast was obtained to provide an estimate of recording noise. Power spectral density analysis of the ERG waveform at each frequency determined amplitude, and fast Fourier transform determined the phase. Additionally, photopic stimulus response functions and responses to long duration (100 and 150 ms) stimuli were obtained.
At the fundamental frequency, the temporal response function for amplitude in the control subjects had a peak at ~ 31 to 42 Hz and a decrease in amplitude at both lower and higher frequencies. In patients, the average amplitude at 10 Hz was normal, but at all other frequencies it was significantly lower than in the controls. For the second harmonic, amplitudes were significantly lower than in controls at all frequencies. The phase in VGB patients for both the fundamental and second harmonic showed a significant phase lag at lower frequencies and no relative phase shift at higher frequencies (> 32 Hz). The average phase delay for low frequencies (10 to 31 Hz) was 13 ms, 6 ms and 5 ms for the fundamental frequency, and 8 ms, 8 ms and 7 ms for the second harmonic. These delays in phase are similar to the delay in implicit time of the photopic b- and d- wave for the long flash response (~9 and 12 ms).
In these VGB patients, abnormalities in the amplitude and phase of the flicker response provide further evidence of altered interplay in the ON and OFF activity in post-receptor retina.
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