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J.-M. Rizk, M.-A. Lefebvre, J. Knypinski, C. Beaulieu, P. Lachapelle; To Blink or Not to Blink: Is There a Diagnostic Use to the Photomyoclonic Artifact (PMA)?. Invest. Ophthalmol. Vis. Sci. 2008;49(13):2226.
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While the PMA or blink is viewed as a contamination of the clinical electroretinogram (ERG), sometimes it is the only sign left attesting that the patient saw the flash. We examined if it could be used as a diagnostic tool.
Photopic ERGs (flash intensities:-1.2 to 2.84 log cd.sec.m-2 in 14 steps; background: 30 cd.m-2) were recorded from 6 normal subjects who were instructed to blink at each flash (voluntary blink: Vblink). Responses were recorded using two different bandwidths : 1-1000 Hz (broadband ERG) and 100-1000 Hz (OP bandwidth). This data was compared to recordings selected from our clinical data bank (normal and pathological recordings; N>100) with evidence of a reflex blink (Rblink).
The Vblink generates a signal of high voltage (compared to the corresponding b-wave) culminating between 170-240 msec after flash onset (depending on flash intensity) on the broadband ERG recordings. Peak time measurements are however significantly facilitated when the OP recording bandwidth is used, where bursts of electrical activity corresponding to the onset of the blink response (R or V) occurred at latencies varying between 50-70 msec for an increase in flash intensity of 4 log-units in photopic condition. In comparison, the timing of the photopic b-wave lengthened from 25 to 32 msec during the same intensity interval. The timing of the blink response (R or V) was time locked to the strength of the stimulus, irrespective of the state of retinal adaptation (photopic Vs scotopic). Analysis of pathological tracings allowed us to identify the following diagnostic categories: normal ERGs with normal or delayed Rblink, delayed ERGs with delayed Rblink and flat ERGs with normal or delayed Rblink.
Results indicate that the PMA can be considered as an evoked potential to the same extent as the ERG or the VER. Its use (voluntary or reflexive) could represent a valuable addition to the visual electrophysiology armamentarium, especially in cases where the ERG suggests an extinguished retinal function while the patient still demonstrates visually guided behaviors.
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