The association between time spent outdoors and myopia in children and adolescents: a systematic review and meta-analysis.
OBJECTIVE
To summarize relevant evidence investigating the association between time spent outdoors and myopia in children and adolescents (up to 20 years).


METHODS
Systematic review and meta-analysis.


METHODS
Results from 7 cross-sectional studies were pooled in a meta-analysis. A further 16 studies (8 cross-sectional not meeting criteria for meta-analysis; 7 prospective cohort studies; 1 randomized, controlled trial [RCT]) were reported in the systematic review.


METHODS
The literature search included 4 databases (Medline, Embase, Web of Science, and Cochrane Central Register of Controlled Trials [CENTRAL]), and reference lists of retrieved studies. Estimates of association were pooled using random effects meta-analysis. We summarized data examining the association between time spent outdoors and prevalent myopia, incident myopia, and myopic progression.


METHODS
Pooled odds ratios (ORs) and 95% confidence intervals (CIs) for myopia for each additional hour spent outdoors per week from a meta-analysis.


RESULTS
The pooled OR for myopia indicated a 2% reduced odds of myopia per additional hour of time spent outdoors per week, after adjustment for covariates (OR, 0.981; 95% CI, 0.973-0.990; P<0.001; I(2), 44.3%). This is equivalent to an OR of 0.87 for an additional hour of time spent outdoors each day. Three prospective cohort studies provided estimates of risk of incident myopia according to time spent outdoors, adjusted for possible confounders, although estimates could not be pooled, and the quality of studies and length of follow-up times varied. Three studies (2 prospective cohort and 1 RCT) investigated time spent outdoors and myopic progression and found increasing time spent outdoors significantly reduced myopic progression.


CONCLUSIONS
The overall findings indicate that increasing time spent outdoors may be a simple strategy by which to reduce the risk of developing myopia and its progression in children and adolescents. Therefore, further RCTs are warranted to investigate the efficacy of increasing time outdoors as a possible intervention to prevent myopia and its progression.
Department of Public Health and Primary Care, University of Cambridge, Cambridge, UK. justincsherwin@gmail.com
Justin C
JC
Sherwin
Mark H
MH
Reacher
Ruth H
RH
Keogh
Anthony P
AP
Khawaja
David A
DA
Mackey
Paul J
PJ
Foster
D000293:Adolescent; D002648:Child; D003430:Cross-Sectional Studies; D018450:Disease Progression; D004777:Environment; D015444:Exercise; D006801:Humans; D015994:Incidence; D007899:Leisure Activities; D009216:Myopia / Q000453:epidemiology / Q000517:prevention & control*; D016017:Odds Ratio; D015995:Prevalence; D011446:Prospective Studies; D013997:Time Factors; D055815:Young Adult