Objective Measurement of Light Exposure and Refractive Error in Children

Purpose: An increase in outdoor time in high ambient light levels has been found to be protective against myopia onset in multiple studies. Objective measurements of light exposure and physical activity can more accurately quantify factors partially leading to myopia progression. In this one year longitudinal study, a wrist-worn device was used for continuous measurements of light exposure, physical activity and sleep to compare with subjective measurements. Objective data were also evaluated between parents and children, and across school and summer sessions.

Methods: Children (n = 60) wore an actigraph device continuously for three two-week sessions to quantify light exposure, activity, and sleep. Spherical equivalent refractive error (SER) of the cycloplegic autorefraction was measured at baseline to classify subjects by refractive error. Parents answered an activity questionnaire, and a subset of parents also wore an actigraph device to compare parent-child behaviors (n = 33). Actigraph data were compared to subjective data from the questionnaire. Additionally, children’s objective data were analyzed by season.

Results: Average age (±SD) of subjects at enrollment was 7.60 ± 1.80 years. At baseline there were 5 hyperopes, 47 emmetropes, and 8 myopes enrolled. By the end of the study, 3 hyperopes, 47 emmetropes, and 10 myopes were present. Average SER was +0.86 ± 1.40 D at baseline (ranging from -2.41 to +7.75 D). Objective measurements of daily light exposure showed that children spent an average of 1:24 ± 0:04 (hr:min) outdoors during school sessions and 1:48 ± 0:06 hr:min during summer sessions. The amount of time spent outdoors in the summer was significantly greater than the fall (p < 0.001) and spring (p < 0.05). Myopes were found to have spent 0:39 hr:min less per day outdoors during the summer session than emmetropes, although this did not reach statistical significance (p = 0.055). Subjectively, parents underestimated time outdoors during school sessions by 0:19 hr:min (p < 0.001) and a significant correlation was found between parent and child time spent outdoors (p < 0.05). Physical activity and sleep were not significantly different between seasons.

Conclusion: Significant differences in light exposure across school and summer sessions were observed. Additionally, the significant relationship between parent and child outdoor time suggests the possible presence of a behavioral component to the development of myopic refractive errors. Future studies with increased numbers of emmetropic and myopic children utilizing objective measurement techniques may serve to clarify the role of light exposure in myopia pathophysiology and provide behavioral recommendations for children to prevent myopia and slow progression.