title: Time spent in outdoor activities in relation to myopia prevention and control: a meta-analysis and systematic review.
abstract: Outdoor time is considered to reduce the risk of developing myopia. The purpose is to evaluate the evidence for association between time outdoors and (1) risk of onset of myopia (incident/prevalent myopia); (2) risk of a myopic shift in refractive error and c) risk of progression in myopes only. A systematic review followed by a meta-analysis and a dose-response analysis of relevant evidence from literature was conducted. PubMed, EMBASE and the Cochrane Library were searched for relevant papers. Of the 51 articles with relevant data, 25 were included in the meta-analysis and dose-response analysis. Twenty-three of the 25 articles involved children. Risk ratio (RR) for binary variables and weighted mean difference (WMD) for continuous variables were conducted. Mantel-Haenszel random-effects model was used to pool the data for meta-analysis. Statistical heterogeneity was assessed using the I2test with I2≥ 50% considered to indicate high heterogeneity. Additionally, subgroup analyses (based on participant's age, prevalence of myopia and study type) and sensitivity analyses were conducted. A significant protective effect of outdoor time was found for incident myopia (clinical trials: risk ratio (RR) = 0.536, 95% confidence interval (CI) = 0.338 to 0.850; longitudinal cohort studies: RR = 0.574, 95% CI = 0.395 to 0.834) and prevalent myopia (cross-sectional studies: OR = 0.964, 95% CI = 0.945 to 0.982). With dose-response analysis, an inverse nonlinear relationship was found with increased time outdoors reducing the risk of incident myopia. Also, pooled results from clinical trials indicated that when outdoor time was used as an intervention, there was a reduced myopic shift of -0.30 D (in both myopes and nonmyopes) compared with the control group (WMD = -0.30, 95% CI = -0.18 to -0.41) after 3 years of follow-up. However, when only myopes were considered, dose-response analysis did not find a relationship between time outdoors and myopic progression (R2= 0.00064). Increased time outdoors is effective in preventing the onset of myopia as well as in slowing the myopic shift in refractive error. But paradoxically, outdoor time was not effective in slowing progression in eyes that were already myopic. Further studies evaluating effect of outdoor in various doses and objective measurements of time outdoors may help improve our understanding of the role played by outdoors in onset and management of myopia.
authors.affiliation: Department of Preventative Ophthalmology, Shanghai Eye Disease Prevention and Treatment Center, Shanghai Eye Hospital, Shanghai, China.|Department of Ophthalmology, Shanghai General Hospital, Shanghai Jiao Tong University, Shanghai, China.
authors.forename: Shuyu
authors.initials: S
authors.lastname: Xiong
authors.affiliation: Brien Holden Vision Institute, Sydney, New South Wales, Australia.|School of Optometry and Vision Science, University of New South Wales, Sydney, New South Wales, Australia.
authors.forename: Padmaja
authors.initials: P
authors.lastname: Sankaridurg
authors.affiliation: Brien Holden Vision Institute, Sydney, New South Wales, Australia.
authors.forename: Thomas
authors.initials: T
authors.lastname: Naduvilath
authors.affiliation: Department of Nutrition, Shanghai Municipal Center for Disease Control and Prevention, Shanghai, China.
authors.forename: Jiajie
authors.initials: J
authors.lastname: Zang
authors.affiliation: Department of Preventative Ophthalmology, Shanghai Eye Disease Prevention and Treatment Center, Shanghai Eye Hospital, Shanghai, China.|Department of Ophthalmology, Shanghai General Hospital, Shanghai Jiao Tong University, Shanghai, China.
authors.forename: Haidong
authors.initials: H
authors.lastname: Zou
authors.affiliation: Department of Preventative Ophthalmology, Shanghai Eye Disease Prevention and Treatment Center, Shanghai Eye Hospital, Shanghai, China.
authors.forename: Jianfeng
authors.initials: J
authors.lastname: Zhu
authors.affiliation: Department of Preventative Ophthalmology, Shanghai Eye Disease Prevention and Treatment Center, Shanghai Eye Hospital, Shanghai, China.
authors.forename: Minzhi
authors.initials: M
authors.lastname: Lv
authors.affiliation: Department of Preventative Ophthalmology, Shanghai Eye Disease Prevention and Treatment Center, Shanghai Eye Hospital, Shanghai, China.|Department of Maternal and Child Health, School of Public Health, Key Laboratory of Public Health Safety, Ministry of Education, Fudan University, Shanghai, China.
authors.forename: Xiangui
authors.initials: X
authors.lastname: He
authors.affiliation: Department of Preventative Ophthalmology, Shanghai Eye Disease Prevention and Treatment Center, Shanghai Eye Hospital, Shanghai, China.|Department of Ophthalmology, Shanghai General Hospital, Shanghai Jiao Tong University, Shanghai, China.
authors.forename: Xun
authors.initials: X
authors.lastname: Xu
mesh_terms: D006801:Humans; D007899:Leisure Activities; D009216:Myopia / Q000517:prevention & control*; D013997:Time Factors
keywords: dose-response analysis; meta-analysis; myopia; outdoor time