Objectively Measured Light Exposure in Emmetropic and Myopic Adults.
Level 3 - non-randomized controlled study
Non-randomized observational cohort study comparing light exposure between refractive groups across seasons.
PubMed 27811524 · doi:10.1097/OPX.0000000000001013
What was done
Fifty-five adults aged 21–65 years (18 emmetropic, 37 myopic) wore a wrist-worn actigraph device (Actiwatch Spectrum) continuously for 14 days to objectively measure light exposure, activity, and sleep. Participants also completed an activity questionnaire to compare subjective reports against objective recordings. In addition, devices were calibrated against a lux meter and UV sensor across indoor and outdoor settings in different seasons.
What was found
Participants spent an objectively measured 1:52 ± 0:56 hours per day outdoors. Subjective questionnaire responses overestimated objective outdoor time by 0:25 ± 1:19 hours per day (range -1:49 to +4:29 hours, P < .05). Participants spent 1:04 hours more outdoors per day in summer than in winter, receiving a significantly increased cumulative light dose (P < .005). No significant differences in objective outdoor time were observed between myopic and emmetropic subjects. Device illumination measures strongly correlated with lux meter readings (R = 0.99, P < .001), ranging from 142 ± 150 lux for indoor artificial light to 176,497 ± 20,310 lux outdoors in summer.
Why it matters
This study demonstrates that self-reported activity questionnaires substantially misestimate actual outdoor light exposure, highlighting the necessity of objective wearable sensors for environmental vision research.
Limits
The sample size was small (n = 55) with uneven refractive groups (18 emmetropes vs. 37 myopes). The cross-sectional design in adults assesses established refractive states rather than active childhood myopia development, and wrist-worn sensors approximate ambient exposure rather than direct retinal illumination.
Cited by
- supports Indoor bedroom lighting provides a couple hundred lux, whereas outdoor daylight provides thousands of lux.