A recent study published in JAMA Ophthalmology has found evidence suggesting an association between green space structures and lower incidence of myopia—even after controlling for geography and demographics and adjusting for outdoor time and other known risk factors.
Give me some background first.
Recent research has suggested that children in cities have a higher prevalence of myopia than children living in rural areas, and several studies have linked greater outdoor time with decreased myopia prevalence.
Now, talk about the study.
This prospective cohort study assessed the 2-year cumulative change in myopia prevalence of school children at 110 schools in Shenzhen, China, and compared that with the landscape metrics using normalized difference vegetation index (NDVI), an indicator of overall greenness.
Who was included in the study?
The study assessed 138,735 students in grades 1-4 (6-9 years) drawn from 113 schools in the Bao-an district of Shenzhen.
Students were excluded if they reported a history of wearing rigid contact lenses or of medical treatment or disease that could affect vision or vision development.
Findings?
The study found a reduced risk of myopia among students at schools with more green space. This included:
- a larger greenness proportion
- larger areas of green space
- better connectivity between green patches
- more aggregated green space
- less fragmented green space
- shorter distance between patches
This negative association held for both the school level and the individual level.
Expert opinion?
“A better understanding of the relationship between green space morphology and myopia is not only valuable for health, education, and urban planning but can also provide a blueprint for creating a sustainable environment by optimizing the application of land use,” wrote the study authors.
Limitations?
The study authors acknowledged several limitations, the first among them being the use of noncycloplegic autorefraction, which can tend to overestimate myopia. Additionally, the study itself could only indicate correlations, not causation.
In generating the NDVIs, the study authors used high-resolution remote sensing images, but captured only 2 cloud-free scenes during the study period; furthermore, analyzing eight green space morphology indicators could have increased the probability of false positives.
Take home.
Increased outdoor time is a known factor in reduced myopia risk. Detailed studies like this, the authors argue, are a crucial first step in developing sustainable, scalable population-based myopia prevention strategies.