Troland-based and luminance-based flicker ERGs change with pupil size (
Fig. 3). The slopes are in opposite directions, as increasing pupil size for luminance-based tests increases the retinal stimulation, but the SCE causes Troland-based tests to overestimate the retinal stimulation at larger pupil sizes. For Troland-based tests on eyes without chemical dilation (Td undilated, percent of 95% reference interval [RI]) (
Fig. 3), the changes in the ERGs were 1% to 7% of the 95% RI, a minor effect. In absolute terms, the changes in the ERGs for Troland stimulation without dilation were 0.1 ms, 0.4 ms, 4%, and 5%. depending on the measurement. If stronger Troland stimuli were used, pupil diameters without chemical dilation were smaller, leading to even less variability caused by the SCE (
Supplementary Fig. S5). For luminance-based tests on dilated eyes, the changes in ERGs were 15% to 43% of the reference range (candela (cd) dilated, percent of 95% RI) (
Fig. 3), a much larger effect. In absolute terms, the changes in the ERGs for luminance-based tests on dilated subjects were 0.8 ms, 1.9 ms, 63%, and 54% depending on the measurement (cd dilated, change) (
Fig. 3). If both dilated and natural pupil sizes are considered, Troland-based ERGs varied by 7% to 34% of the 95% RI—in absolute terms, 0.4 ms, 1.9 ms, 28%, and 32% (Td all pupil) (
Fig. 3). For rod-based ERG recordings, the SCE does not exist.
14,22 These same Troland and luminance ERG models can be used to analyze these tests by setting ρ = 0, as shown in
Supplementary Figure S4. In these cases, Troland-based ERGs had no dependence on pupil size, whereas the luminance-based ERGs had an even greater dependency on pupil size, because the SCE reduced the effectiveness of increasing pupil size. Considering only dilated pupils, the variations in the ERG measurement were 1 ms, 3.1 ms, 73%, and 66% for times and amplitudes, respectively.