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Anthony Fanous, Allison Dorfman, Mathieu Gauvin, Pierre Lachapelle; Can we assess the visual function in a blink?. Invest. Ophthalmol. Vis. Sci. 2018;59(9):5030.
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© ARVO (1962-2015); The Authors (2016-present)
Although the photomyoclonic artifact (PMA) is viewed as a contaminant of the electroretinogram (ERG), it is often the only sign of visual detection that one can record, especially in patients affected with severe retinopathies such as advanced Retinitis Pigmentosa, where the ERG is nearly extinguished. Given the potential diagnostic use of the PMA, we aimed to optimize its recording and analysis.
PMA were recorded using the same electrode configuration as that used for the recording of the ERG: a DTL on both eyes (within the inferior conjunctival bag) with reference and ground electrodes at the external canthi and forehead respectively. Normative data was collected from normal subjects (N=33) using photopic ERG recordings (Flash intensities ranged from 1-100 cd.s.m-2 delivered against a photopic background of 30 cd.m-2). Waveform components were measured in the time (ms) and amplitude (µV) domain as well as in the time-frequency (Hz) domain using the Discrete Wavelet Transform (DWT). This data was selected from our clinical data bank (normal and pathological recordings; N>100).
In normal subjects, the typical PMA includes an initial burst of 10.7±3.5 ms in duration composed of a series of low voltage (< ± 50 µV) high frequency (40-160 Hz) positive and negative components which ends with a large negative deflection at 74.9±4.7 ms. This initial fast component (IFC) is then followed by a slow (20 Hz range) positive component (SPC) of significantly larger amplitude (200-900 µV) which peaks around 100-125 ms after flash onset. In some examples, the IFC was not followed by the SPC suggesting that they represented two distinct phases of the PMA response. Pathological recordings, where the ERG was extinguished but a PMA was still present, revealed that the timing of the different components of the PMA was usually more affected than their respective amplitude.
Our results reveal that the PMA represents a highly reproducible evoked response composed of two independent phases. We believe that the IFC most probably reflects neuronal activities and the SPC, muscular contraction. Study of pathological recordings clearly indicates that the recording and analysis could add significant diagnostic and prognostic information in the managing of patients with visually debilitating conditions.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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