Altitudinal distribution of myopia: big data analysis based on biogeographic regions in India

Abstract Objective Considering the potential role of various aspects of light on myopia, we aimed to investigate the altitudinal distribution of myopia based on 10 distinctive biogeographic regions in India. Methods This cross-sectional retrospective study involved analysis of refractive error and demographics of 135,927 individuals with myopia aged 11–30 years seen at a large multi-tiered ophthalmology network in India captured through electronic medical records. Using the refractive error of the eye with worse vision in either eye, individuals were classified as having low (-0.5D to -5.75 D), or high myopia (≤ -6.0D). Residential districts were assigned a biogeographical zone using nationally reported boundaries and altitude was determined using Google Earth at the geographic centroid. Descriptive statistics, hypothesis testing, and multiple ordinal logistic regression analysis were performed. Results While low myopia was not associated with altitude, a trend of increased risk of high myopia was observed with higher altitudes. Compared to living at an altitude of 0-100m, the odds of having high myopia compared was 0.96 in the 101-250m range (95% CI: 0.93, 0.99), 2.31 times higher for 251-500m (95% CI: 2.21, 2.42), 1.28 times higher for 501-750m (95% CI: 1.25, 1.32), and 1.62 times higher for > 750m (95% CI: 1.30, 2.04). Conclusions The smaller proportion of high myopes observed in lower altitudes compared to those living in higher altitudes hints at a possible association of altitude with myopia which needs further exploration.