Highland environment and genetic background are associated with myopia risk in Tibetans and Hans

This study aimed to investigate the relationship of high-altitude environmental features and ethnic Tibetan background with myopia.

This cross-sectional study was conducted at highland and lowland sites. The highland sites were located on the Chinese Tibetan Plateau, approximately 4000 m above sea level. A total of 3634 Tibetans and 377 Hans were included in the highland group. The lowland group was from the Yaoxi community, in Wenzhou City, located 10-20 m above sea level, where 176 Han individuals were included. Non-cycloplegic spherical equivalent refraction (SER) and biochemical function tests were measured.

Age-specific myopia prevalence was highest in highland Hans, followed by lowland Hans and highland Tibetans. Among participants in the highland group, including Tibetans and Hans, increased risk of moderate and high myopia was associated with gender [OR (95% CI): 0.47 (0.23, 0.97) for females], education level [OR (95% CI): 3.62 (1.76, 7.45) for middle school education and above], and elevated mean haemoglobin per red blood cell (MCH) [OR (95% CI): 8.04 (1.04, 62.34)]. Among Han participants in both groups, only elevated mean corpuscular volume (MCV) [OR (95% CI): 5.91 (1.00, 34.92)] was associated with increased risk of moderate and high myopia.

The higher prevalence of myopia in Hans compared to Tibetans, and in highland Hans compared to lowland Hans, suggests that both ethnicity and high-altitude environment influence myopia development, potentially through gene-environment interactions. Elevated MCV and MCH levels, particularly in highland Hans, may serve as biomarkers for risk, warranting further investigation.