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Swetha Dhanireddy, Jason Park, Philip Nolan, Dingcai Cao, J Jason McAnany; Dark-adapted 15-Hz Flicker Electroretinograms Measured With Rod-isolating Stimuli. Invest. Ophthalmol. Vis. Sci. 2013;54(15):6121.
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© ARVO (1962-2015); The Authors (2016-present)
The 15-Hz flicker electroretinogram (ERG) measured under dark-adapted conditions has been used to assess rod pathway function, but there is a possibility for cone involvement in the response to high luminance flicker. This study evaluated the rod and cone contributions to the dark-adapted 15-Hz flicker ERG across a broad range of stimulus luminances by comparing ERGs recorded with rod-isolating and non-rod-isolating flicker.
Following 30 minutes of dark-adaptation, full-field 15-Hz flicker ERGs were obtained from four normally-sighted subjects (ages 25 to 35 years) using a 4-primary LED-based stimulating system and standard ERG recording techniques. The 4 primaries were either modulated in phase (non-rod-isolating flicker) or were modulated in different phases to achieve rod-isolation by means of triple silent substitution (rod-isolating flicker). ERGs were measured for a broad range of luminances (-2.0 to 1.8 log scotopic cd/m2 in 0.2 log units steps) for both stimulus types. Fourier analysis was used to obtain the amplitude and phase of the fundamental response component for each stimulus luminance.
The function relating response amplitude to stimulus luminance had three limbs: (1) below -1.0 log scotopic cd/m2, amplitudes were small for both stimulus types; (2) between -1.0 and 1.0 log scotopic cd/m2, the amplitude functions had a similar bandpass shape for both stimulus types; (3) above 1.0 log scotopic cd/m2, amplitude increased sharply for the non-rod-isolating stimuli and was constant for the rod-isolating stimuli. Similarly, the function relating phase to stimulus luminance had three limbs: (1) below -1.0 log scotopic cd/m2, phase was approximately constant for both stimulus types; (2) near -1.0 log scotopic cd/m2, phase decreased sharply for both stimulus types; (3) above 1.0 log scotopic cd/m2, phase increased gradually for the non-rod-isolating stimuli and was approximately constant for the rod-isolating stimuli.
At low luminances, non-rod-isolating and rod-isolating flicker produced similar amplitude and phase functions that exhibited two limbs, which have previously been attributed to destructive interference between signals generated by different rod pathways. For high luminances, the amplitude and phase functions differed for the two stimulus types, suggesting a cone contribution to the non-rod-isolating stimuli that was absent for the rod-isolating stimuli.
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