Findings from a recent study published in JAMA Network Open evaluated the association between outdoor exposure patterns and the development of myopia in school-aged children.
Give me some background.
The trend of earlier onset of myopia among school-aged children suggests an increasingly serious epidemic of high and pathologic myopia in the future.
As previously reported by Glance, prior research has demonstrated that spending more time outdoors is an effective intervention for myopia.
- These studies emphasized the impact of daily time outdoors and sunlight intensity in preventing the onset of myopia.
Bring it back to the study.
However, there remain uncertainties surrounding the necessary requirements for outdoor exposure patterns to impact myopic shift.
Consequently: Researchers tested various outdoor exposure patterns to optimize current outdoor intervention strategies in school-aged children by identifying patterns associated with less myopic shift.
Talk about the study.
In this 1-year prospective cohort study, investigators performed a secondary analysis of the Shanghai Time Outside to Reduce Myopia (STORM) trial, which was a school-based intervention study that recruited students to track their time spent outdoors with smartwatches.
The Storm trial ran from October 2016 to December 2018, and the investigators of this study reviewed the data collected between December 2017 and December 2018.
Tell me more.
Included in the analysis were children without myopia at baseline who consistently wore a smartwatch for a minimum of 6 hours daily (sustained for at least 90 days) and had complete information on variables (e.g., age, sex, axial length, spherical refraction equivalence).
- The average spherical equivalence and axial length at baseline were 1.26 D and 22.74 mm, respectively.
Additionally: There were 12 outdoor exposure patterns analyzed, ranging from ≤4 min and ≤1,999 lux to ≥15 minutes and ≥4,000 lux.
Findings?
In total, 2,976 students (mean age: 7.2 years; 1,525 girls [51.2%]) were included.
The mean daily time outdoors was 90 minutes, and the mean sunlight intensity was 2,345 lux.
What about differences in outdoor exposure patterns?
Of the 12 outdoor exposure patterns, the majority of children spent time outdoors for at least 15 minutes, which made up 74.9% of the total minutes spent outdoors (33,677,584 of 45,016,800 minutes).
Only patterns with at least 15 minutes accompanied with no less than 2,000 lux were associated with less myopic shift in refraction:
- ≥15 minutes and 2,000-3,999 lux
- Myopic shift: -0.007 D (95% confidence interval [CI] -0.011 to -0.002 D)
- ≥15 minutes and ≥4,000 lux
- Myopic shift: -0.006 D (95% CI -0.010 to -0.002 D)
Expert opinion?
These findings indicate that the protective effect of time spent outdoors on myopia prevention is linked with increasing sunlight intensity once it is higher than 2,000 lux.
“Such moderate light-level conditions are easily attainable in most outdoor environments during daylight hours, under various street lighting (6,000-16,000 lux) or even tree shade (5,556-7,876 lux) conditions,” noted the study authors.
As such: A practical recommendation for myopic patients would be to encourage longer time outdoors as much as possible, even under moderate light intensities.
Limitations?
These included:
- The findings may not be directly generalizable to other geographic areas because the study was limited to Shanghai
- A 1-year longitudinal study may not be sufficient to identify the associations between outdoor exposure patterns and myopic shift
- The use of smartwatches to estimate light levels may lead to underestimation compared with the actual light levels that reached the participants’ eyes
Take home.
Future outdoor exposure interventions should focus not only on the overall time spent outdoors but also on the outdoor exposure patterns to prevent myopia in children.