Light- and dark-adapted electroretinograms (ERGs) and ocular pigmentation: comparison of brown- and blue-eyed cohorts

Abstract

This study characterizes differences in human ERGs based on ocular pigmentation. Light- and dark-adapted luminance-response (LR) series for a-, b- and i-waves and light-adapted oscillatory potentials (OPs) were recorded in 14 healthy volunteers (7 blue-eyed Caucasians; 7 brown-eyed Asians, aged 20-22 years). Amplitude interpolations were by logistic growth (Naka-Rushton), Gaussian or the combined 'photopic hill' functions. Implicit times (IT) for dark-adapted a- and b-waves, and for light-adapted a-, b- and i-waves were earlier in the blue-eyed group than in the brown-eyed group across all flash strengths (P < 0.05). For dark-adapted ERGs, saturated a-wave amplitude was larger for blue eyes (397 vs. 318 μV, P < 0.05) as was the a-wave to strong flash (10 cd·s/m(2); 357 vs. 293 μV, P < 0.05) and the b-wave to ISCEV standard 0.01 (354 vs. 238 μV, P < 0.05). Light-adapted b-waves for midrange flash stimuli were much larger for the blue-eyed group (photopic hill, Gaussian peak: 155 vs. 82 μV, P < 0.001) with no difference in saturated amplitudes. Similarly, interpolated i-wave amplitudes were larger (48 vs. 18 μV, P < 0.01). For a light-adapted 2.6 stimulus, a- and b-waves were larger for the blue-eyed group (52 vs. 39 μV; 209 vs. 133 μV, P < 0.01) as were OP4 and OP5 (37.2 vs. 15.6 μV; 47.5 vs. 22.2 μV, P < 0.01), but OP1-OP3 did not differ. ERGs have shorter ITs in people with blue irides than in those with dark pigmentation. Amplitude differences are highly non-linear and substantially larger from eyes with light pigmentation for components thought to be associated with the OFF retinal pathways.

Light-Adapted Electroretinogram Differences in Autism Spectrum Disorder

“…The iris color index was computed as a ratio of the 25 th centile gray values obtained from two 1 mm line segments centered vertically from the pupil margin to the 25 th centile gray scale values of the pupil diameter. The ratio (iris color index) provided an objective measure of iris pigmentation for each eye because darker irises absorb more light and reduce the ERG waveform amplitudes (Al Abdlseaed et al 2010). The mean iris color index was 1.26(0.12) for the control group and 1.21(0.10) for the ASD group.…”

ISCEV extended protocol for the stimulus–response series for light-adapted full-field ERG

“…The addition of this extended protocol for the LA ERG stimulus-response series may improve the characterisation of LA retinal function, potentially enabling detection of more subtle changes such as early progression of disease or toxicity. For example, the method may reveal abnormalities to weaker and/or stronger flashes that are not evident in the standard LA 3.0 ERG and allows more comprehensive assessment of an abnormality detected with standard ERGs [3][4][5][6].…”

“…Plotting the series may facilitate identification of inconsistencies and outliers, particularly if the data are noisy. (i) Ocular pigmentation There is evidence that fullfield ERG waveforms have larger amplitudes in those with lower levels of ocular pigmentation; the differences in amplitude associated with pigmentation have been shown to be the greatest for LA b-waves in some studies of the LA stimulus-response function [5,17].…”

“…This requires sufficient data to define the hill and plateau regions of the curve (4). Other options include fitting selected regions of the function, either the rising phase using a logistic curve (5) or the hill portion of the curve using a Gaussian curve.…”

Effects of DTL electrode position on the amplitude and implicit time of the electroretinogram

“…Factors that may influence the absolute ERG results, but will have little effect on intersession variability because they do not differ between sessions, include gender [5], refraction [6], and ocular pigmentation [7]. Other factors that can affect the intersession variability may be minimized by always incorporating International Society for Clinical Electrophysiology of Vision (ISCEV) standards.…”