Constant luminance (cd·s/m2) versus constant retinal illuminance (Td·s) stimulation in flicker ERGs
C Quentin Davis, Olga Kraszewska, Colette Manning, C Quentin Davis, Olga Kraszewska, Colette Manning
Abstract
Purpose: To compare the effect of variable pupil size on the flicker electroretinogram (ERG) between a stimulus having constant luminance and a stimulus having constant retinal illuminance (constant Troland) that compensates for pupil size.
Methods: Subjects (n = 18) were tested with 12 pairs of the stimuli. The stimulus pair consisted of the ISCEV standard constant luminance stimulus (3 cd·s/m2 with a 30 cd/m2 background) and a constant retinal illuminance stimulus (32 Td·s with a 320 Td background) selected to provide the same stimulus and background when the pupil diameter is 3.7 mm. Half the subjects were artificially dilated, and their response was measured before and during the dilation. The natural pupil group was used to assess intra- and inter-subject variability. The artificially dilated group was used to measure the flicker ERG's dependence on pupil size.
Results: With natural pupils, intra-subject variability was lower with the constant Troland stimulus, while inter-subject variability was similar between stimuli. During pupil dilation, the constant Troland stimulus did not have a dependence on pupil size up to 6.3 mm and had slightly larger amplitudes with longer implicit times for fully dilated pupils. For the constant luminance stimulus, waveform amplitudes varied by 22% per mm change in pupil diameter, or by 48% over the 2.2 mm diameter range measured in dilated pupil size. There was no difference in inter-subject variability between constant Troland natural pupils and the same subjects with a constant luminance stimulus when dilated (i.e., the ISCEV standard condition).
Conclusions: These results suggest that a constant Troland flicker ERG test with natural pupils may be advantageous in clinical testing. Because of its insensitivity to pupil size, constant Troland stimuli should produce smaller reference ranges, which in turn should improve the sensitivity for detection of abnormalities and for monitoring changes. In addition, the test can be administered more efficiently as it does not require artificial dilation.
Clinical trial registration number: This trial is registered at ClinicalTrials.gov (NCT02466607).
Keywords: Dilation; Flicker electroretinogram (ERG); Mydriasis; Pupil; Reference range; Troland.
Conflict of interest statement
Conflict of interestThese conflicts of interest are relevant to this research: employment (Q. Davis and O. Kraszewska), stock ownership (Q. Davis), and study sponsorship by LKC Technologies, Inc. C. Manning has no conflict of interest.
Ethical approvalAll procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki Declaration and its later amendments or comparable ethical standards. Informed consent was obtained from each subject after explanation of the nature and possible consequences of the study. The study was approved by an institutional review board (SAIRB-15-0017) and is registered at ClinicalTrials.gov (NCT02466607).
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