Children from urban areas have a 2.6-times higher odds of having myopia than those from rural areas, researchers in China recently reported. “Rural areas are characterized by more green environments. A potential association between green space and myopia may exist, but it hasn’t been thoroughly investigated,” they noted in a recent study, which they conducted in Shenzhen, the largest immigrant city in China and one currently undergoing rapid urbanization.
Using a new development—spatial technology—the group was able to monitor, compute and analyze green space based on satellite data and remote sensing technology. They drew other data from the Environmental Health and Myopia Prevention and Control Project, which evaluates the impact of environmental factors on myopia development.
A total of 113 Shenzhen schools participated in the study between 2016 and 2019. The researchers looked specifically at annual eye refraction data of schoolchildren in grades one to four (six- to nine-year-olds). “They represent a period of rapid refractive error changes,” the researchers noted. A total of 142,865 children (56.4% boys) met inclusion criteria and had reliable data.
Here are some of the findings:
- Of the participants, 17,646 (12.4%) had myopia with an average sphere + ½ cylinder (SER) of -1.636D at baseline.
- The total schools had an average myopia prevalence of 11.9%.
- According to school socioeconomic ranking information, there were 24 (21.2%) key schools, 52 (46%) moderate schools and 37 (32.7%) normal schools at baseline.
The researchers reported, “At baseline, no association with green space exposure was observed for any of the other covariates that were assessed at school level (e.g., male percentage, average age, average SER, myopia prevalence, school socioeconomic status), for myopia or for SER at an individual level.”
At the final data collection, 118,369 (82.9%) students participated. Analysis of an association “between green space exposure and school- and individual-level outcomes showed that at the school level, a 0.1-increase in green space exposure was associated with a 3.6%-lower increase in school myopia prevalence over two years, after adjusting for covariates.”
Individual refraction at baseline demonstrated that a 0.1-increase in green space in the non-myopic group was associated with a 19.8%-reduction in myopia risk. In the myopic group, green space exposure wasn’t associated with progression.
The researchers administered an additional questionnaire to a random sample of 8,400 students, which was completed by 7,996 parents. After adjusting for additional covariates, such as paternal and maternal myopia, screen time, reading time and outdoor activity, the researchers found that a 0.1-increase in green space exposure was associated with a 27.9%-reduction in myopia risk in non-myopic children. However, green space exposure wasn’t significantly associated with myopia progression over two years among myopic students.
The researchers concluded that there’s a negative association between green space exposure and myopia and that there aren’t any interactions or correlations between green space exposure and other known risk factors.
“If the green spaces of all schools were increased to 0.3 or above, the overall myopia prevalence would be reduced by about four percentage points per year,” the researchers explained. “This would be sufficient to achieve the ideal myopia prevalence reduction suggested by the Ministry of Education in China. Additionally, our study demonstrates that satellite imaging can mitigate the challenge of quantifying the environmental exposures at a macroscopic level by elucidating medical patterns using remotely sensed data. Such methods can be further extended to study the relationship between the global environment and human vision health.”
Yang Y, Chen W, Xu A, et al. Spatial technology assessment of green space exposure and myopia. Ophthalmology. August 2, 2021. [Epub ahead of print].