May 1, 2023
By Luke Seesink, B. Applied Science, BHVI
This study aimed to assess the impact of increased time spent outdoors on myopia onset and progression in primary school children over a two-year period. The study employed a prospective, cluster-randomized, examiner-masked, three-arm trial design and included a total of 6,295 students aged 6 to 9 years from 24 primary schools in Shanghai, China. The test groups were allocated an additional 40 or 80 minutes of outdoor time per school day, while the control group continued their habitual outdoor time.
The results showed that the adjusted incidence of myopia decreased by 16% and 11% in test groups I and II, respectively, compared to the control group. Moreover, both test groups showed less myopic progression and axial elongation compared to the control group. The protective effect of outdoor time was found to be related to the duration of exposure and light intensity, with a daily outdoor time of 120 to 150 minutes at 5,000 lux/minutes or cumulative outdoor light intensity of 600,000 to 750,000 lux, significantly reducing the incidence risk ratio by 15%-24%. However, the dose-response effect between test groups I and II was not observed.
Overall, this study provides valuable insights into the protective effect of outdoor time on myopia onset and progression in primary school children, highlighting the importance of properly monitoring compliance with outdoor intervention to achieve the protective effect. The study’s findings could have significant implications for public health policies aimed at reducing myopia incidence and its associated risks.
Time Outdoors in Reducing Myopia: A School-Based Cluster Randomized Trial with Objective Monitoring of Outdoor Time and Light Intensity
Xiangui He, PhD, Padmaja Sankaridurg, PhD, Jingjing Wang, PhD, Jun Chen, PhD, Thomas Naduvilath, PhD, Mingguang He, PhD, Zhuoting Zhu, PhD, Wayne Li, MD, Ian G. Morgan, PhD, Shuyu Xiong, PhD, Jianfeng Zhu, MD, Haidong Zou, MD, Kathryn A. Rose, MD, Bo Zhang, MS, Rebecca Weng, GD, Serge Resnikoff, MD, Xun Xu, MD
Purpose: To evaluate the efficacy of time outdoors per school day over two years on myopia onset and shift.
Design: A prospective, cluster-randomized, examiner-masked, three-arm trial.
Participants: A total of 6,295 students aged 6 to 9 years from 24 primary schools in Shanghai, China, stratified and randomized by school in a 1:1:1 ratio to control (n = 2,037), test I (n = 2,329), or test II (n = 1,929) group.
Methods: An additional 40 or 80 minutes of outdoor time was allocated to each school day for test I and II groups. Children in the control group continued their habitual outdoor time. Objective monitoring of outdoor and indoor time and light intensity each day was measured with a wrist-worn wearable during the second-year follow-up.
Main outcome measures: The two-year cumulative incidence of myopia (defined as cycloplegic spherical equivalent [SE] of ≤-0.5 diopters [D] in the right eye) among the students without myopia at baseline and changes in SE and axial length (AL) after two years.
Results: The unadjusted two-year cumulative incidence of myopia was 24.9%, 20.6%, and 23.8% for control, test I, and II groups, respectively. The adjusted incidence decreased by 16% (incidence risk ratio [IRR], 0.84; 95% confidence interval [CI], 0.72-0.99; P = 0.035) in test I and 11% (IRR = 0.89; 95% CI, 0.79-0.99; P = 0.041) in test II when compared with the control group. The test groups showed less myopic shift and axial elongation compared with the control group (test I: -0.84 D and 0.55 mm, test II: -0.91 D and 0.57 mm, control: -1.04 D and 0.65 mm). There was no significant difference in the adjusted incidence of myopia and myopic shift between the two test groups. The test groups had similar outdoor time and light intensity (test I: 127 ± 30 minutes/day and 3,557 ± 970 lux/minute; test II: 127 ± 26 minutes/day and 3,662 ± 803 lux/minute) but significantly more outdoor time and higher light intensity compared with the control group (106 ± 27 minutes/day and 2,984 ± 806 lux/minute). Daily outdoor time of 120 to 150 minutes at 5,000 lux/minutes or cumulative outdoor light intensity of 600,000 to 750,000 lux significantly reduced the IRR by 15%～ 24%.
Conclusions: Increasing outdoor time reduced the risk of myopia onset and myopic shifts, especially in nonmyopic children. The protective effect of outdoor time was related to the duration of exposure and light intensity. The dose-response effect between test I and test II was not observed, probably because of insufficient outdoor time achieved in the test groups, which suggests that proper monitoring of compliance on outdoor intervention is critical if one wants to see the protective effect.
He, X., Sankaridurg, P., Wang, J., Chen, J., Naduvilath, T., He, M., … & Xu, X. (2022). Time outdoors in reducing myopia: a school-based cluster randomized trial with objective monitoring of outdoor time and light intensity. Ophthalmology, 129(11), 1245-1254.
|Luke Seesink is a Senior Clinical Research Manager at the Brien Holden Vision Institute. He has first-class honors from a B. Applied Science (Orthoptics) degree at the University of Sydney. He has worked for almost 20 years as a qualified orthoptist and in different clinical research roles within ophthalmology.|