Effect of pupil size on fixed-luminance flicker full-field electroretinogram magnitude

Abstract

Purpose : Diopsys® NOVA fixed-luminance flicker full-field electroretinogram (ffERG) is a potential alternative to classic ffERG testing for measuring the electrical activity of cone cells . Pupil size has been shown to effect electrical response. The index study aims to quantify the relationship between pupil size and ffERG magnitude using this device.

Methods : 12 patients (24 eyes) with no known ocular diseases were enrolled in the study. Retinal activity was examined using Diopsys® ffERG before and after dilation. Eyes were initially anesthetized with proparacaine hydrochloride 0.5 % ophthalmic solution and then dilated with tropicamide 1% and phenylephrine 2.5% ophthalmic solutions. Eyes were dilated to a minimum of 5 mm before Diopsys® measurements were made. Paired t-test and robust linear regression were performed on the data set.

Results : Mean age was 34.9±8.4 years and 25% were female. Mean value of pupil diameter and magnitude before and after the dilation was 2.54 ± 0.38 mm/7.01 ± 0.90 mm and 10.45 ± 2.92 µV /16.56 ± 4.1 µV , respectively. There was a statistically significant difference in magnitude of response before and after dilation (p: <0.0001). In dilated eyes, linear regression analysis demonstrated an increase in magnitude with each millimeter increase of pupil size (r²: 0.44; Coeff.: 2.99; p: <0.0001) (figure1). It also demonstrated a 12% increase in change of magnitude with each millimeter unit increase in pupil size (r²: 0.15; Coeff.: 1.12; p: 0.07) (figure2).

Conclusions : Pupil size affects electrophysiologic response of the retina and should be measured and documented. Physicians should take pupil size into consideration when making clinical judgments based on Diopsys® ffERG. The normative values for ffERG devices should include pupil size variability to ensure better clinical judgments.

This is a 2021 ARVO Annual Meeting abstract.

 

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