Rod and cone contributions to the dark-adapted 15-Hz flicker electroretinogram

Purpose To evaluate rod and cone contributions to the dark-adapted 15-Hz flicker electroretinogram (ERG) across a broad range of stimulus luminances by comparing rod-isolating (ERGR), cone-isolating (ERGC), and non-receptor-specific (ERGR?C) responses. Methods Dark-adapted, full-field 15-Hz ERGs were obtained from four normally sighted subjects (ages 29–36 years) using a four-primary LED-based stimulating system. The primaries were either modulated sinusoidally in phase (ERGR?C) or were modulated in counter-phase to achieve rod isolation (ERGR) or cone isolation (ERGC) by means of triple silent substitution. Measurements were made for a broad range of luminances (-2.5 to 1.8 log scot. cd/m2 in 0.2 log unit steps). Fourier analysis was used to obtain the amplitude and phase of the fundamental response component at each stimulus luminance. Results Stimulus luminance had different effects on response amplitudes and phases under the three paradigms. Specifically, ERGC amplitude and phase increased monotonically as luminance increased. The effects on ERGR?C and ERGR were complex: ERGR?C and ERGR amplitude was small and the phase decreased for low luminances, whereas amplitude and phase increased sharply at moderate luminances. For high luminances, ERGR?C amplitude and phase increased, whereas ERGR amplitude decreased and phase was approximately constant.