Continuous Objective Assessment of Near Work, Light Exposure, and Activity

Purpose: Myopia, or nearsightedness, is an epidemic, with up to 90% of the population in urbanized countries affected. Myopia brings with it potentially blinding complications and significant socio-economic burden. Light exposure and near work are known risk factors for myopia. However, evidence regarding the role of near work in myopia is conflicting. Current technology allows for objective measurements of light exposure; however, quantification of near work is assessed via questionnaires, which are subject to poor recall, response, and parent biases. The purpose of this study was to introduce the RangeLife, a novel, custom device developed for continuous, objective measurement of near work. Further, the objective near work output was compared to traditional visual activity questionnaires and activity logs. Methods: We developed the RangeLife, a device for continuous, objective measurement of working distance. Four devices were built, calibrated, and validated. Then, adult subjects wore the device on weekdays and weekend days, while simultaneously wearing an actigraph device for objective measurements of light exposure and activity. Subjects maintained an activity log and answered a visual activity questionnaire. RangeLife data were downloaded and binned into 0.10 m intervals. Objective diopter hours (dh), a weighted measure of near work, were calculated and compared with subjective diopter hours obtained from the questionnaire. Results: Diopter hours for all subjects were significantly higher on weekdays (14.73 ± 4.67 dh) compared to weekends (11.90 ± 4.84 dh, p = 0.05). 94 ± 1.85% of near and intermediate viewing distances were recorded when the subjects were exposed to mesopic and indoor photopic light levels (<1000 lux), and 80.03 ± 2.11% during periods of sedentary physical activity (<320 counts per minute). Subjective reports of time viewing near and intermediate distances significantly overestimated objective measures (p = 0.002).
Conclusions: The RangeLife was shown to provide reliable measures of viewing distance, and can be further utilized to understand potential influences of viewing behaviors on refractive error.