Spatial technology measures association between green space exposure, myopia
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Using satellite imaging techniques, researchers were able to establish an association between green space exposure at school and the change in school-specific myopia prevalence.
Even a relatively small increase in green space exposure was associated with a nearly 30% lesser risk for non-myopic children to develop myopia.
The study was conducted in Shenzhen, China, a large city that is undergoing rapid urbanization with many families migrating from the surrounding rural areas. One hundred thirteen primary schools, including children aged between 6 and 9 years, participated in the study, and the green space surrounding them was detected and quantified using satellite imaging. Each school was classified based on the normalized difference vegetation index, a measure of green space calculated from the visible and near-infrared light reflected by vegetation with values ranging between –1 and 1, with higher numbers indicating a higher level of green space.
“Green space within school areas was used for the analysis because Chinese students spend most of their day at schools (at least 9 hours in primary school),” the authors wrote.
For each child, refraction was measured at baseline, between 2016 and 2017, and 2 years later, between 2018 and 2019. Out of 142,865 children, 17,646 (12.4%) had myopia at baseline, with an average of 1.6 D; 118,369 children (82.9%) participated in the final data collection.
In the non-myopic group and after adjusting for covariates such as family history of myopia, screen time and reading time per day, and outdoor activity after school, the model showed that a 0.1 increase in green space exposure was associated with a 27.9% reduction in the risk of developing myopia. In the myopic group, the model showed that green space exposure was not associated with myopia progression over 2 years.
This study provides “a potential basis for the development of prevention strategies targeting the onset of myopia,” according to the authors. Based on their analysis, an increase of green spaces of all schools to 0.3 or above would reduce the overall myopia prevalence by about 4 percentage points per year.
“The implications are relevant to policymakers as greater access to green space potentially provides eye health benefits, which may help contain the exploding epidemic of myopia in an increasing number of countries worldwide,” they wrote.
Perspective
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It is clear from previous studies that as populations become more urban and less rural, the incidence of childhood myopia increases. In a 2006 study published in the Journal of Epidemiology and Public Health, urban children were 2.6 times more likely to develop myopia when compared with those in rural environments. Could this higher rate of myopia be related, in part, to the reduced green space in cities compared with the rural countryside? This study used satellite imaging to analyze and quantify green space in schools and then used examinations and questionnaires to quantify myopia in those schools. One hundred thirteen schools in Shenzhen, the largest immigrant city in China, participated, and data from 143,000 students were analyzed. The correlation of myopia development and myopia progression with green space exposure was calculated at both the school level and the individual level.
The take-home message of this large study is that increased green space exposure can reduce myopia development. The study found that a 10% increase in school green space was associated with a nearly 20% decrease in myopia development (P < .0001). However, for children who were already myopic at the beginning of the study, the amount of green space exposure was not associated with the amount of myopia progression.
This study provides additional evidence that green space exposure at schools can lead to a decrease in new cases of myopia. Physicians will continue to advocate for improved designs for urban schools to increase green space. This study adds to the growing evidence that green space has eye health benefits for children. Based on the study data, an increase in green space to 30% of the footprint, in all schools, would result in a decrease of new cases of myopia by about 4 percentage points per year.
The multifactorial nature of myopia incidence and progression needs continuing analysis and study. Satellite imagery can determine the green space percentage of a school’s footprint, but per student exposure to that green space still needs further analysis. Designing in green space must be paired with a curriculum that emphasizes usage of the green space to achieve the goal of reducing myopia and myopia progression.
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