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.