Environment & Lifestyle

Effect of Time Spent Outdoors on the Development of Myopia

By Rohit Dhakal
Research Collaborator, Brien Holden Vision Institute
PhD student- LVPEI and City, University of London

Myopia has reached an epidemic level in young adults in many urban East and Southeast Asian countries. The economic burden associated with myopia as well as the risk of sight-threatening complications at higher levels has triggered an alarm for ways to control myopia. Although, various optical and non-optical anti-myopia strategies are available to slow myopia, increasing time spent outdoors was thought to have a protective effect on myopia (either prevent or delay onset of myopia).1-3 This study aimed to assess the efficacy of improved time outdoors in preventing onset of myopia.

The trial was a cluster randomized, school-based trial conducted in Guangzhou, China for more than 3 years. Overall, 29 schools were selected and categorized into 6 strata based on similarity in uncorrected visual acuity distribution of children from class 1 to 6. From each strata, two schools were randomly selected and allocated to either test or control group resulting in a total of 12 schools. Increasing time outdoors was implemented by two modes: a) an additional 40 minutes of outdoor time at the end of the school day on weekdays, and b) engaging students in more outdoor activities on weekends or holidays. A total of 1903 (952 in intervention and 951 in control group) students were enrolled, of which 87 withdrew by the end of 3 years. Children were examined at baseline and every 1-year interval at the same time of the year (October to November). Information on risk factors for myopia, parental myopia and child’s daily activities were collected using questionnaires. The primary outcome was the 3 years cumulative incidence rate of myopia in the intervention and control group and secondary outcome was the change in mean SER error and axial length in a period of 3 years.

The baseline characteristics were similar across the groups except for mean age (6.61 ± 0.33 years in intervention vs. 6.57 ± 0.32 years in control group, p=0.01), axial length (22.6 ± 0.71 vs. 22.66 ± 0.7 mm, p=0.05) and proportion of myopic parents (53.6% vs. 59.8%, p<0.01). At the end of 3 years, 30.4% (259 among 853 eligible participants at baseline) in the intervention group and 39.5% (287 among 726 eligible participants at baseline) in control group developed myopia. The odds of developing myopia in 3 years were 0.73 (95% CI, 0.57 to 0.92, p=0.01) in test compared to control group after adjustment for parental myopia. At the end of 3 years, change in SER from the intervention group was significantly less (-1.42 D vs. -1.59 D respectively, p=0.04), whereas, amount of total change in axial elongation was not significantly different in the two groups (0.95 mm; 95% CI- 0.91 to 1.00 vs 0.98 mm, 95% CI- 0.94 to 1.03 in intervention vs control group).

Based on the evidence, it can be concluded that an extra 40 minutes of outdoor activity reduces the incidence of myopia. Although there was a difference in SE between test and control groups, there were no differences for axial length change. Being outdoors has positive health benefits and considering children from different age and ethnic groups will allow for generalizability of these findings for a common public health policy (additional time in outdoors during school hours) across different countries.

 

Abstract
He M, Xiang F, Zeng Y, Mai J, Chen Q, Zhang J, Smith W, Rose K, Morgan IG

importance: Myopia has reached epidemic levels in parts of East and Southeast Asia. However, there is no effective intervention to prevent the development of myopia.

Objective: To assess the efficacy of increasing time spent outdoors at school in preventing incident myopia.

Design, setting, and participants: Cluster randomized trial of children in grade 1 from 12 primary schools in Guangzhou, China, conducted between October 2010 and October 2013.

Interventions: For 6 intervention schools (n = 952 students), 1 additional 40-minute class of outdoor activities was added to each school day, and parents were encouraged to engage their children in outdoor activities after school hours, especially during weekends and holidays. Children and parents in the 6 control schools (n = 951 students) continued their usual pattern of activity.

Main outcomes and measures: The primary outcome measure was the 3-year cumulative incidence rate of myopia (defined using the Refractive Error Study in Children spherical equivalent refractive error standard of ≤-0.5 diopters [D]) among the students without established myopia at baseline. Secondary outcome measures were changes in spherical equivalent refraction and axial length among all students, analyzed using mixed linear models and intention-to-treat principles. Data from the right eyes were used for the analysis.

Results: There were 952 children in the intervention group and 951 in the control group with a mean (SD) age of 6.6 (0.34) years. The cumulative incidence rate of myopia was 30.4% in the intervention group (259 incident cases among 853 eligible participants) and 39.5% (287 incident cases among 726 eligible participants) in the control group (difference of -9.1% [95% CI, -14.1% to -4.1%]; P < .001). There was also a significant difference in the 3-year change in spherical equivalent refraction for the intervention group (-1.42 D) compared with the control group (-1.59 D) (difference of 0.17 D [95% CI, 0.01 to 0.33 D]; P = .04). Elongation of axial length was not significantly different between the intervention group (0.95 mm) and the control group (0.98 mm) (difference of -0.03 mm [95% CI, -0.07 to 0.003 mm]; P = .07).

Conclusions and relevance: Among 6-year-old children in Guangzhou, China, the addition of 40 minutes of outdoor activity at school compared with usual activity resulted in a reduced incidence rate of myopia over the next 3 years. Further studies are needed to assess long-term follow-up of these children and the generalizability of these findings.

He M, Xiang F, Zeng Y, Mai J, Chen Q, Zhang J, Smith W, Rose K, Morgan IG. Effect of time spent outdoors at school on the development of myopia among children in China: a randomized clinical trial. Jama. 2015 Sep 15;314(11):1142-8.

References

  1. Rose KA, Morgan IG, Ip J, et al. Outdoor activity reduces the prevalence of myopia in children. Ophthalmology. 2008;115(8):1279-1285.
  2. Jones LA, Sinnott LT, Mutti DO, Mitchell GL, Moeschberger ML, Zadnik K. Parental history of myopia, sports and outdoor activities, and future myopia. Investigative ophthalmology & visual science. 2007;48(8):3524-3532.
  3. Wu P-C, Tsai C-L, Wu H-L, Yang Y-H, Kuo H-K. Outdoor activity during class recess reduces myopia onset and progression in school children. Ophthalmology. 2013;120(5):1080-1085.
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