Myopia prevalence and ocular biometry in children and adolescents at different altitudes: a cross-sectional study in Chongqing and Tibet, China

Objective To investigate the differences in myopia prevalence and ocular biometry in children and adolescents in Chongqing and Tibet, China.Design Cross-sectional study.Setting The study included children and adolescents aged 6–18 years in Chongqing, a low-altitude region, and in Qamdo, a high-altitude region of Tibet.Participants A total of 448 participants in Qamdo, Tibet, and 748 participants in Chongqing were enrolled in this study.Methods All participants underwent uncorrected visual acuity assessment, non-cycloplegic refraction, axial length (AL) measurement, intraocular pressure (IOP) measurement and corneal tomography. And the participants were grouped according to age (6–8, 9–11, 12–14 and 15–18 years group), and altitude of location (primary school students: group A (average altitude: 325 m), group B (average altitude: 2300 m), group C (average altitude: 3250 and 3170 m) and group D (average altitude: 3870 m)).Results There was no statistical difference in mean age (12.09±3.15 vs 12.2±3.10, p=0.549) and sex distribution (males, 50.4% vs 47.6%, p=0.339) between the two groups. The Tibet group presented greater spherical equivalent (SE, −0.63 (−2.00, 0.13) vs −0.88 (−2.88, –0.13), p