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Y. Shen, J. Racine, J. M. Little, P. Lachapelle; Facilitatory Interactions Evidenced With the Multifocal ERG. Invest. Ophthalmol. Vis. Sci. 2010;51(13):1482.
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© ARVO (1962-2015); The Authors (2016-present)
The mfERG technique allows one to stimulate discrete regions of the posterior pole in order to identify foci of retinal anomaly. The stimulus consists of a varying number of hexagons that compose a mosaic. The area of the hexagon increases in size with eccentricity within the mosaic in order to always stimulate the same number of retinal cells. We examined to see if the amplitude of the mfERG response elicited by one large hexagon that covered the entire mfERG field equaled that of the sum of the smaller mfERG responses generated by a given mosaic.
mfERGs evoked to stimuli consisting of 1, 7, 19, 37 and 61 hexagons were obtained from normal subjects (n=5) and patients affected with selected maculopathies (n=6). The amplitude of the mfERG response elicited by the 1 hexagon stimulus was compared to the sum of the mfERG responses elicited by the 7, 19, 37 and 61 hexagon stimuli, respectively.
The amplitude of the mfERG response increased by 37±11% (p<.05) from 1 to 7 hexagons, by 6±3% (p>.05) from 7 to 19 hexagons, by 3±2% (p>.05) from 19 to 37 hexagons and by 0.7±7% (p>.05) from 37 to 61 hexagons, for a total increase of 49±8% (p<.05) from 1 to 61 hexagons. Of interest, augmenting the number of hexagons from 1 to 61 slightly increased the total retinal area stimulated by 17%. In comparison, the mean 1 to 61 hexagons amplitude increment measured in our patient group was 36±10% with some patients showing significantly smaller increment (<25%) and others larger ones (>50%).
The amplitude of the mfERG response evoked from a large hexagon stimulus, one that covers the entire mfERG field, is significantly smaller than that of the sum of mfERG responses evoked when the mfERG field is broken down into 61 hexagons, suggesting a facilitatory effect. Most of the effect is observed with the initial breakdown (1 to 7 hexagons). Although the retinal origin of this effect remains to be identified, results obtained from patients affected with selected maculopathies suggest that the latter effect may allow us to further differentiate maculopathies of various etiologies.
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