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A new cohort study in China reports suggests the structure of green space decreased the relative risk of myopia among school-aged children.
A recent prospective cohort study found overall green space morphology was associated with a decreased relative risk of myopia over a two-year period among primary school students aged 6 to 9 years in China.1
The analysis of high-resolution satellite images revealed a well-arranged green space with larger areas, better connectivity, increased aggregation, lower fragmentation, and a shorter distance between green patches was linked to slower progression of school-aged myopia.
“Principal component analysis of 7 relevant landscape metrics demonstrated an association with smaller increases in school myopia prevalence and incident myopia at the individual level, suggesting that the landscape structure as a whole was negatively associated with myopia development,” wrote the investigative team, led by Haotian Lin, MD, PhD, State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center.
Global estimates indicate the number of individuals with myopia will increase to nearly 5 billion by 2050.2 Prevention efforts to ameliorate the rise in cases prioritize the role of environmental factors in delaying onset and slowing progression on a large scale, particularly for young children. Prior literature has indicated that urban-dwelling children have a higher prevalence of myopia, while green space exposure at school has been inversely associated with spectacle use.
Citing these data, Lin and colleagues noted more deliberate planning of green space may improve the visual health of school-aged children, particularly given the rapid urbanization of China.1 The study team’s previous investigation using remote sensing technology showed each 0.1-unit increase in normalized vegetation index (NDVI) was associated with an approximate 28% reduction in myopia risk.3
However, the team indicated green space with the same NDVI may exhibit different functions and utility for health, owing to changes in morphology.1 They noted the association between myopia risk and specific geometry and distribution characteristics of green space has not yet been explored. Lin and colleagues' current analysis evaluated that association using a study population of children in grades 1 to 4 from the Environmental Health and Myopia Prevention and Control Project in Shenzen, China.
Baseline data (2016 to 2017) and year 2 (2018 to 2019) data were utilized for the assessment of outcomes in the current analysis. The analysis’ main outcomes consisted of the two-year cumulative change in myopia prevalence at each school and the incidence of myopia at the student level after 2 years. A total of eight landscape metrics were obtained using cloud-free Gaofen-2 satellite data from 2016 and 2019 to analyze area, aggregation, and the shape of green space.
At baseline, a total of 138,735 students were assessed from September 2016 to June 2017. Of this population, 115,350 (83.1%) were followed up 2 years later from September 2018 to June 2019. Upon analysis, the study team found a higher proportion, aggregation, and an increased cohesion index were each associated with a slower increase in school myopia rate.
In the analysis, a 1-unit increase in the myopia-related green space morphology index showed 1 SD higher in the proportion of the total and largest green space patches, increased aggregation, improved connectivity, greater segmentation, and shorter distances between patches. Within the principal component regression, at the school level, a 1-unit increase in the myopia-related green space morphology index was associated with a lower change in myopia prevalence (–1.7%; 95% CI, -2.7 to -0.6; P = .002).
Meanwhile, at the individual level, a 1-unit increase in myopia-related green space morphology index was associated with a 9.8% (95% CI, 4.1 to 15.1; P < .001) reduction in the risk of myopia incidence among students without myopia at baseline. After further adjustment for outdoor activity, screen and reading time, and parental myopia, Lin and colleagues found an increase in myopia-related green space morphology index was associated with an 11.8% (95% CI, 3.1 to 19.6; P = .009) reduction in indent myopia.
“Following our previous report on the association between mean normalized difference vegetation index and slower myopia progression, we believe that these underlying green space morphological characteristics, which were captured in previous studies, could be informative for population-based urban planning strategies to prevent myopia,” Lin and colleagues wrote.