Design and Baseline Data of the Guangzhou Child and Adolescent High Myopia Study.

PURPOSE: To establish a longitudinal, school-based cohort to investigate physiological and pathological ocular changes and identify associated risk factors in children and adolescents with high myopia in South China. METHODS: This three-year cohort recruits students aged 6-18 years from 1,438 schools in Guangzhou, China (April 2018-August 2024). Eligible participants have a cycloplegic spherical equivalent (SE) ≤-3.00 D (ages 6-8) or ≤-6.00 D (ages 9-18). Annual follow-up includes demographic, behavioural, and familial questionnaires and comprehensive ophthalmic assessments, including visual acuity, ocular biometry, cycloplegic refraction, fundus photography, and optical coherence tomography/angiography. The study adheres to the Declaration of Helsinki and was approved by the Ethics Committee of Zhongshan Ophthalmic Centre (approval number: 2017KYPJ100). Written informed consent is obtained from all participants and their guardians. Generalized estimating equations and mixed-effect models assess ocular changes and associations with environmental and biometric factors. RESULTS: 1,331 participants were enrolled at baseline (mean SE= -7.34 ± 2.38 D; axial length = 26.21 ± 1.30 mm). Older age was associated with more myopic SE (β= -0.26, p < 0.001) and longer axial length (β = 0.18, p < 0.001). Males had longer axial length (β = 0.42, p < 0.001), and higher corneal power was linked to shorter axial length (β= -0.29, p < 0.001). Behavioural factors showed no significant associations with SE or axial length. CONCLUSIONS: These baseline preliminary analyses show that demographic factors and corneal power, rather than behavioural factors, are significantly associate with ocular dimensions in early-onset high myopia. This longitudinal cohort provides a vital platform to track ocular growth, early pathological changes, and progression risk factors.