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 I 2 test with I 2 ≥ 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 (R 2 = 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.

Physical activity and myopia in Danish children—The CHAMPS Eye Study

“…We believe as evidence suggests that time outdoors remain the most important factor (Xiong et al. ). There is, however, an inherent confusion in the topic due to the close relation between PA and outdoor activity.…”

Knowledge, perspectives and clinical practices of Australian optometrists in relation to childhood myopia

“…The majority (almost 90 per cent) of respondents also considered increasing the time spent outdoors to be beneficial for reducing myopia progression. While ensuring adequate (greater than two hours/day) outdoor time is a protective factor for myopia development, its potential efficacy as an ‘intervention’ for reducing myopia progression is less certain . As summarised in a systematic review and meta‐analysis by Xiong et al, most studies to date have not shown clear benefit.…”

Optical mechanisms regulating emmetropisation and refractive errors: evidence from animal models

“…Numerous studies have observed that increased ambient illumination is protective for FDM in animal models, and time outdoors is protective for myopia in children . The mechanisms of the protective effects of light are unknown, and might include both neurochemical factors, such as alterations in melanopsin and dopamine cascades, and optical factors, such as miosis‐induced increased depth of field, a flatter dioptric scene, and spectral distribution of sunlight and chromatic cues.…”