Dec. 3, 2019
Krupa Philip, BOptom, PhD
Research Scientist, Brien Holden Vision Institute
With myopia and high myopia leading to sight-threatening complications, it is critical to sieve out the leading risk factors for myopia genesis and progression. Attributed to be a result of both genetic and environmental factors, the rapid rise in myopia prevalence in recent decades is suggestive of a dominant role for environmental factors. Indeed, data from animal models show that form deprivation and optical defocus can regulate eye growth. Additionally, human clinical data for myopia prevalence by urban versus rural location, impact of indoor-outdoor activity and seasonal variation in eye growth suggest environmental influences at play.
A meta-analysis of five prospective intervention trials in children aged 6 to 18 years was performed to identify the effect of outdoor activities on the incidence and progression of myopia. Only those studies that have a clearly defined intervention group with different levels of outdoor activities and a non- intervention group (control group) at the beginning of the study were included in this meta-analysis. The outcomes considered were relative risk of myopia, myopic shift rate in 1 year and axial elongation rate in 1 year. Children were grouped according to their initial refractive status: initial myopes, initial nonmyopes, or mixed.
The researchers found that the risk of myopia development was lower in children with more hours of outdoor activities per week. The overall rate of myopic shift was slower in the intervention group compared to control group [0.13 diopter/year; 95% Confidence Interval (CI) 0.08, 0.18 diopter/year]. The treatment effect was higher in initially non-myopic children. Axial length elongation was slower in the intervention group compared to the control group, with average axial elongation being – 0.03 mm/year [95% CI 0.00, 0.05 mm/year].
This meta-analysis showed that more outdoor activities lowered the risk of myopic onset and also decreased the rate of myopic shift and reduced axial length elongation. Authors propose increased dopamine levels, decrease in image blur, chromaticity of sunlight, or more uniform dioptric space outdoors associated with increased outdoor activities at play in preventing or slowing the incidence and progression of myopia.
Effect of Outdoor Activities in Myopia Control: Meta-analysis of Clinical Studies; Li Deng and Yi Pang
Significance: Our meta-analyses assess the benefit of outdoor activities on myopia onset and myopic shift among school-aged children reported in prospective intervention studies.
Purpose: The purpose of this study was to investigate the reduced risk of myopia development, myopic shift, and axial elongation with more outdoor activity time among school-aged children.
Methods: A literature search was conducted using PubMed, MEDLINE, Scopus, EMBASE, Vision Cite, and Cochrane Library. Five clinical trials met our selection criteria. Three outcome variables were used to assess the benefit of intervention: relative risk (RR), difference in myopic shift rate, and difference in axial elongation rate. Meta-analyses were applied to each outcome variable under the random-effects model. Children were grouped according to their initial refractive status: initial myopes, initial nonmyopes, or mixed.
Results: The pooled RR indicates that there is a reduced risk of developing myopia with more hours of outdoor activities per week (RR, 0.66; 95%confidence interval [CI], 0.49 to 0.89). The overall rate of myopic shift rate was slower in the intervention group compared with the control group (0.13 diopter/y; 95%CI, 0.08 to 0.18). The axial elongation was also slower (−0.03 mm/y; 95% CI, −0.05 to −0.00). The benefit of slowing myopic shift was observed in all initially nonmyopic cohorts (three of three) and most of the initially myopic cohorts (two of three).
Conclusions: The meta-analysis results suggest that there is a slightly lower risk of myopia onset and myopic shift with more hours of outdoor activities. Future clinical trials are needed to assess its long-term effect and whether the effect varies by initial myopic status.
Source: Li Deng and Yi Pang (2019). Effect of Outdoor Activities in Myopia Control: Meta-analysis of Clinical Studies. Optom Vis Sci 2019;96:276–282. doi:10.1097/OPX.0000000000001357