Lhasa childhood eye study: the rationale, methodology, and baseline data of a 5 year follow-up of school-based cohort study in the Tibetan plateau region of Southwest China

Tibetan Plateau is a highland area with special geographical location, time zone, and ethnic composition. We herein report the rationale, methodology and baseline data of the school-based childhood cohort study named Lhasa Childhood Eye Study (LCES), with the primary objective to pursue a comprehensive understanding on the longitudinal trends of refractive error as well as other ocular diseases and to address the differences between Tibetan Plateau and other parts of the world. Grade one students from primary schools in Lhasa were cluster randomly selected. They were examined and would be conducted with follow-up annually for 5 years. The examination procedures for LCES consisted of standardized ocular, systematic examinations, and questionnaires, identical to the Anyang Childhood Eye Study (ACES) conducted in central China. One thousand nine hundred two Grade one students eligible for the LCES, 1856 (97.58%) participated in the study, with a mean age of 6.83 ± 0.46 years (range 5.89-10.32 years), and the proportions of male to be 53.02%. 1762 (94.93%) of the 1856 participants in the baseline exam were Tibetans. 1837 (98.98%) of the students examined had cycloplegic autorefraction performed. The numbers of hyperopia, emmetropia, myopia, and high myopia were 127 (6.91%), 1639 (89.22%), 71 (3.86%) and 3 (0.16%) respectively. Compared with ACES, students from LCES baseline had a younger age (p