Is myopia prevalence related to outdoor green space?

Rapid urbanisation and lifestyle changes have been associated with a huge increase in myopia across many parts of the world. There is strong evidence that environmental factors including time outdoors and urbanisation can influence the development of myopia, particularly in school-aged children. The aim of this study is to determine whether there is a relationship between the prevalence of myopia and the amount of vegetation/green spaces across different regions of the world, as a risk factor for myopia development.The prevalence of myopia in the 15 to 19-year age group in Australia, Brazil, China, Finland, India, Iran, Japan, Oman, Singapore, South Africa and the UK was obtained from a meta-analysis by Holden et al. Normalised Difference Vegetation Index (NDVI) was used to quantify green space exposure based on Landsat 7 Enhanced Thematic Mapper Plus (ETM+) satellite data. Green space was measured in locations specific to 15 studies that reported myopia prevalence. Simple linear regression was used to analyse yearly data, and a mixed effects model was applied to assess the significance of green space when study was a random effect.Myopia prevalence increases significantly when green space was <-0.2, but the effect was less apparent for values >-0.1. When a mixed effects model was used, the effect of green space was found to be significantly associated with myopia prevalence (p = 0.05).There was evidence of a weak but significant non-linear relationship between myopia and green space, with the effect most apparent at low levels of green space. A larger data sample, along with further investigations into the utilisation of green spaces, are required to understand whether increasing the amount of green space can reduce myopia incidence and progression impact.