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

Abstract

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 to 36 years) using a 4-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 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. Conclusions At low luminances, the ERGR+C and ERGR functions can be attributed to interactions between two rod pathways. At high luminances, the functions can be accounted for by interactions between rod and cone pathways (ERGR+C) or rod insensitivity (ERGR). The ERGR paradigm minimizes cone intrusion, permitting assessment of rod function over a large range of luminance levels.

Abnormal 8-Hz flicker electroretinograms in carriers of X-linked retinoschisis

“…As discussed elsewhere [23,24], the degree of rod and cone isolation is a potential concern in silent substitution paradigms, like that used in the present study. However, a recent study from our group [23] that used identical 15-Hz rod-isolating, cone-isolating, and combined rod and cone modulating stimuli and instrumentation found good isolation, based on results obtained from a patient who lacked a cone response (i.e.…”

“…The apparatus and stimuli are described in detail elsewhere [22,23]. In brief, full-field stimuli were generated by a Diagnosys Espion E 3 system and presented in a ColorDome desktop ganzfeld (Diagnosys LLC, Lowell, MA).…”

“…The LEDs of the ColorDome were programmed to serve as a four-primary photostimulator with dominant wavelengths of 465 nm (blue), 515 nm (green), 593 nm (amber), and 642 nm (red). The four LEDs were simultaneously modulated sinusoidally in phase to achieve combined rod and cone modulation or in different phases to achieve rod or cone isolation, as defined elsewhere [23,24]. A constant chromaticity was maintained under all three paradigms (CIE 10 o coordinates of x = 0.58 and y = 0.40).…”

“…However, a recent study from our group [23] that used identical 15-Hz rod-isolating, cone-isolating, and combined rod and cone modulating stimuli and instrumentation found good isolation, based on results obtained from a patient who lacked a cone response (i.e. a complete achromat).…”

A method for estimating intrinsic noise in electroretinographic (ERG) signals

“…An ERG stimulus that is repetitive or periodic around a time-averaged light level, however, can be more informative about the (patho-) physiology of the retina instead of a singleflash ERG because continuous recording allows the estimation of the amplitude and phase of the temporal frequency response taking into account the complete recording period instead of maxima and/or minima within predefined time windows. Furthermore, continuous ERGs can be very useful to isolate the responses of a subset of photoreceptors (rods, L-cones, M-cones, S-cones or different combinations) and their postreceptoral pathways [1][2][3][4], or when the stimuli are spatially restricted or inhomogeneous, as in the pattern ERG [5] or multifocal ERG [6,7]. With such paradigms, however, the ERG responses are often small and indistinguishable from noise after a singlestimulus presentation.…”