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Mathias Nittmann, Avinash J Aher, Jan J Kremers, Radouil T Tzekov; Relationship between stimulus size and different components of the electroretinogram (ERG) elicited by flashed stimuli. Invest. Ophthalmol. Vis. Sci. 2019;60(9):2510. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
To investigate how light stimulus conditions of varying spatial sizes affect the photopic negative response (PhNR) and other components of the flash and long-flash electroretinogram (ERG) in normal subjects
Three stimulus conditions were generated by a Ganzfeld photo-stimulator controlled via a RetiPort (Roland Consult) system: a spectrally narrowband red flash on a blue background (ROB), a broadband white flash on white background (WOW), and an L+ M-cone isolating (Cone Iso; 42% L- and 42% M-cone contrast; L- and M-cones modulated in phase) square-wave flicker created by double silent substitution method. ERGs were elicited from nine subjects (7 M, 2 F) recorded via DTL electrode. Each stimulus condition was measured for 7 sizes: full-field (FF), 70°, 60°, 50°, 40°, 30°, and 20° diameter circular stimuli. Amplitude and peak times for the a-wave, b-wave, i-wave, and PhNR were examined as a function of stimulus size, and PhNR to b-wave amplitude ratios were calculated.
With decreasing stimulus size, amplitudes for all ERG waveform components attenuated and peak times increased. The WOW stimulus had the greatest decrease in PhNR amplitude from full-field to 70°, suggesting significant contribution by the peripheral retina for this stimulus condition (FF: 31.7 µV, 70°: 10.7 µV, a 66% decrease, p < 0.01). Compared to WOW, ROB elicited greater PhNR amplitudes at all stimulus sizes smaller than full-field, likely due to more central retina involvement in PhNR generation (70° through 20°, p < 0.01). The peak times for the WOW stimulus occurred earliest for each ERG component except for the PhNR, which had similar peak times for both WOW and ROB conditions. The L and M-cone isolating stimulus consistently elicited the lowest amplitudes and most delayed peak times for the major waveform components, but interestingly also the most robust i-waves. The PhNR: b-wave amplitude ratio was found to increase with decreasing stimulus size for all three testing conditions, with the ROB stimulus producing the largest relative and absolute increases in this ratio (ROB at FF: 0.46, at 20°: 1.30, a 2.8x increase; WOW at FF: 0.27, at 20°: 0.63, a 2.3x increase; Cone Iso at FF: 0.43, at 20°: 0.87, a 2.0x increase).
The PhNR is particularly large when elicited by the central retina. Further studies to explore the clinical applicability of these stimuli are warranted.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
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