The ipRGC-Driven Pupil Response with Light Exposure in Children

Abstract

Purpose : Time spent outdoors has been linked to the development and progression of myopia in children. The protective effects of light may be mediated in part by the intrinsically photosensitive retinal ganglion cells (ipRGCs), which signal environmental light, control pupil size, and entrain circadian rhythm. Here, the ipRGC-driven pupil response was evaluated in children, and examined with refractive error (RE) and light exposure.

Methods : Pupil responses were measured in school-aged children (5-12 yrs, n=11). Subjects wore an actigraph device continuously for one week for objective measures of light exposure prior to pupil measurements. One second (s) long wavelength (LW) light (651nm, 133 cd/m²) and 10 increasing intensities of 1s short wavelength (SW) light (456 nm, 0.167 to 167 cd/m²) were presented to the dilated left eye, and pupil diameter was recorded in the right eye. The 6s post-illumination response (PIPR) was calculated as the relative pupil size 6-7s after light offset. The stimulus response function for intensity vs PIPR was fitted with a piecewise 2-segment linear regression, and the break point was taken as the melanopsin threshold. Cycloplegic RE and axial length (AL) were measured.

Results : Mean RE (± SD) was -0.12±0.8 (+1.2 to -1.4). Subjects spent an average of 80.3±38.3 minutes outdoors per day over the previous week. The 6s PIPR had a graded response to increasing SW light intensities from 0.93±0.01 to 0.65±0.03, with lower values indicating increased ipRGC activity. Mean melanopsin threshold was 5.12 cd/m² (0.84–16.7 cd/m²), which was significantly associated with cumulative light exposure over the previous 24 hours (r²=0.4, p<0.05) and mean time outdoors per day over the previous week (r²=0.4, p<0.05). Additionally, the 6s PIPR was associated with 24 hour light exposure for midrange intensities, 0.87-8.33 cd/m². There were no associations between ipRGC-driven pupil metrics with RE or axial length.

Conclusions : The ipRGC-driven pupil response in children was associated with previous light exposure and time spent outdoors. The melanopsin threshold measured here in young subjects was similar to that measured previously in an adult population. There were no associations between the ipRGC-driven pupil response and RE or axial length in this cohort. However, evidence suggesting that children with myopia spend less time outdoors warrants further longitudinal studies evaluating the role of ipRGCs in eye growth.

This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.