Greater residential greenness was associated with decreased risk of myopia and astigmatism among preschoolers, according to a study published in Environmental Research.
Studies show that limited green spaces in cities are linked to reduced outdoor time. This, in turn, is associated with increased time on screen-based devices, the study says. The researchers hypothesized that young children whose homes had limited residential green space would spend more time on screens and thereby experience a greater risk of developing myopia and astigmatism.
Researchers analyzed the 2019 survey data of primary caregivers of 53,575 preschool children in the Longhua Child Cohort Study. They assessed residential greenness and employed the normalized difference vegetation index (NDVI), as well as satellite images of the participants’ residences. They averaged NDVI within a buffer area of 100 meters, 250 meters, and 500 meters surrounding each residential address.
Based on screenings, myopia was defined as spherical equivalent (SE) equal to or worse than -0.50 D in at least 1 eye, hyperopia if the SE was at least +2.00 D in at least 1 eye, and astigmatism if the cylinder power was at least 1.75 D in at least 1 eye. Primary caregivers reported the diagnosis. The final analysis compared children with diagnosed myopia (at least 0.50 D in 1 eye) or astigmatism (at least 1.75 D in 1 eye) with children who had passed each vision screening. Daily screen time was self-reported and averaged across the first 3 years of life for all devices.
Of the 53,575 included preschoolers, 1236 had myopia and 5347 had astigmatism. Children spent an average of .69 hours on screens per day during the first 3 years of life. Over half of parents had refraction problems.
After adjusting for potential confounders, the researchers found that greater neighborhood greenness in the 100-meter buffer around homes was significantly associated with decreased myopia risk (adjusted odds ratio (AOR) and 95% confidence interval (CI): 0.62, 0.38- 0.99). Greater neighborhood greenness in buffers of 100, 300, 500 meters around the homes were significantly associated with a lower risk of preschool astigmatism.
Per 10% increase in residential greenness for 100-meter buffer zone, myopia risk decreased 3.8% and risk of astigmatism decreased 4.5%. A 10% increase in residential greenness in the 250-meter and 500-meter buffer zones resulted in 4.1% and 3.9% decreased risk of preschool astigmatism, respectively.
In the 100-meter and 250-meter buffers, every 10% increase in greenness was associated with 8 minutes less of screen time per week. Each 1 hour per day increase in screen time during early childhood was associated with a 33% increased risk of preschool myopia and a 23% increased risk of preschool astigmatism.
Limitations of the study included possible recall bias in caregivers’ reporting outcomes of the vision screening, the lack of knowledge of whether children moved home during early childhood, possible changes in green space data measurements, and the NDVI’s inability to describe the use of available green spaces.
“From a public health perspective, these findings highlight the health benefits of green spaces on vision, providing a potential preventative option and early beneficial intervention,” the report explains.
Huang L, Schmid KL, Zhang J, et al. Association between greater residential greenness and decreased risk of preschool myopia and astigmatism. Environmental Research. Published online March 6, 2021. doi: 10.1016/j.envres.2021.110976