June 3, 2019
By Peter Wagner
PhD Student, Brien Holden Vision Institute
A recent meta-analysis by Xiong et al.1 shows a beneficial effect of increased outdoor time with a reduction of risk for myopia development, but surprisingly not for progression.
For this analysis, the authors ranked and analyzed data from studies that were published between 2012 and 2015 and investigated the relationship between outdoor time and myopia (incidence / prevalence / development / progression). Data from studies that provided a high confidence in findings were considered and those that investigated other aspects related to outdoor exposure (e.g. light exposure) were disregarded. Furthermore, only studies with medium to high methodological qualities and high statistical heterogeneity were included.
Out of the 600 ranked articles, 51 articles were considered relevant but just 25 articles met the criteria for inclusion. That included four clinical trials (2945 participants), eight cohort studies (8363 participants) and 13 cross-sectional studies (23112 participants).
The meta-analysis showed that with increased time outdoors there was a significant reduction for the risk of myopia onset. Furthermore, data from three clinical trials showed a reduction in myopic shift with increased outdoor time. However, the dose-response analysis of six relevant studies did not find a protective effect of increased outdoor time for myopia progression.
While the effects of other risk factors and bias of data collection using questionnaires may have influenced the results of individual studies, this meta-analysis suggests an association between times spent outdoors and myopia onset. In other words, “Get out there!”
Time spent in outdoor activities in relation to myopia prevention and control: a meta-analysis and systematic review.
Xiong S, Sankaridurg P, Naduvilath T, Zang J, Zou H, Zhu J, Lv M, He X, Xu X
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 I2 test 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.
Peter Wagner is a PhD student at the Brien Holden Vision Institute.
- Xiong, S., Sankaridurg, P., Naduvilath, T., Zang, J., Zou, H., Zhu, J., … & Xu, X. (2017). Time spent in outdoor activities in relation to myopia prevention and control: a meta‐analysis and systematic review. Acta ophthalmologica, 95(6), 551-566.