The ipRGC-driven pupil response with light exposure and refractive error in children.

Abstract

The intrinsically photosensitive retinal ganglion cells (ipRGCs) signal environmental light, control pupil size and entrain circadian rhythm. There is speculation that ipRGCs may be involved in the protective effects of light exposure in myopia. Here, the ipRGC-driven pupil response was evaluated in children and examined with light exposure and refractive error. Children ages 5-15years participated. Subjects wore an actigraph device prior to the lab visit for objective measures of light exposure and sleep. For pupillometry, the left eye was dilated and presented with stimuli, and the consensual pupil response was measured in the right eye. Pupil measurements were preceded by 5min dark adaptation. In Experiment 1 (n=14), 1s long wavelength light ('red,' 651nm, 167cdm-2 ) and 10 increasing intensities of 1s short wavelength light ('blue,' 456nm, 0.167-167cdm-2 ) were presented with a 60s interstimulus interval. A piecewise two-segment regression was fit to the stimulus response function to determine the functional melanopsin threshold. Pupil responses were analysed with light exposure over the previous 24h. For Experiment 2 (n=42), three 1s red and three 1s blue alternating stimuli were presented with a 60s interstimulus interval. Following an additional 5-min dark adaption, the experiment was repeated. Pupil metrics included peak constriction, the 6s and 30s post-illumination response (PIPR), early and late area under the curve (AUC). Following pupil measurements, cycloplegic refractive error and axial length were measured. For Experiment 1, PIPR metrics demonstrated a graded response to increasing intensity blue stimuli, with a mean functional melanopsin threshold of 6.2±4.5cdm-2 (range: 0.84-16.7cdm-2 ). The 6s PIPR and early AUC were associated with 24-h light exposure for high intensity stimuli (33.3 and 83.3cdm-2 , p<0.005 for both). For Experiment 2, there were no associations between pupil metrics and refractive error. The 6s PIPR and early AUC to blue stimuli were significantly increased for Trial 2 compared to Trial 1. The ipRGC-driven pupil responses in children were robust and similar to responses previously measured in an adult population. The 6s PIPR and early AUC to high intensity blue stimuli were associated with previous light exposure. There were no associations between the ipRGC-driven pupil response and refractive status in this cohort.