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W.A. Watkins, S. Viswanathan; Normal Features and Cellular Origin of the Multifocal Pattern Electroretinogram . Invest. Ophthalmol. Vis. Sci. 2003;44(13):37.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To describe features of normal multifocal pattern electroretinogram (mPERG) waveforms and determine the extent of inner-retinal contributions to these responses. Methods: mPERGs were recorded with a VERIS system (EDI, CA) using DTL electrodes from 10 normal subjects (21-30 yrs). Their pupils were dilated, refractive errors corrected and accommodation blocked. Stimuli consisted of counterphase-modulated triangles arranged in 61-scaled hexagons with Mn luminance 100cd/m 2 & 100% contrast. The stimulus array subtended 31deg vertically and 37deg horizontally at a viewing distance of 48cms. The monitor frame rate was 75Hz, M-sequence exponent 15 with 1 frame/M-step and amplifier cut off frequencies 1 and 100Hz. First order kernel (1K) and first slice of the second order kernel (2K) responses were analyzed. Using the same stimulus conditions mPERG responses were obtained from two anesthetized cynomologous monkeys before and after blockade of inner-retinal responses with tetrodotoxin (TTX) and N-Methyl-D-Aspartic acid (NMDA). Results: 1K responses analyzed in rings showed a negative and then a positive potential. The timing as well as amplitude of the negative potential decreased from center to periphery. The timing of the positive potential did not change from center to periphery while its amplitude reduced. 1K responses analyzed in quadrants showed negative and positive potentials with the positive potentials in the temporal quadrants having broader peaks. 2K responses were larger in size and when analyzed in rings, the central hexagon response showed positive and negative potentials. With increase in retinal eccentricity this positive potential disappeared into the negative trough and simultaneously an earlier positive potential emerged in ring 1 that first increased and then decrease in amplitude towards the periphery. When analyzed in quadrants the 2K responses showed prominent naso-temporal variations, primarily in the form of a positive potential that peaked around 37ms in the temporal field quadrants. The mPERG responses of the monkeys showed similarity to the human responses. Following intravitreal injection of TTX and NMDA the 1K responses were enhanced. The 2K responses were also enhanced in size, mainly in the central 6.5deg but the waveforms had a delayed timecourse. 2K responses were diminished at peripheral locations. Conclusions: mPERG responses contain significant contributions from inner-retinal neurons. Naso-temporal variations in the 2K responses are primarily derived from inner-retinal activity. 1K and 2K responses also contain sizeable contributions from retinal neurons located more distally.
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