Prevalence and associated factors of screening-defined myopia among schoolchildren in Urumqi: a comparison of two cross-sectional surveys conducted in 2012 and 2019.

BACKGROUND: Myopia is an important public health concern among schoolchildren. This study described the prevalence of screening-defined myopia and its associated factors among schoolchildren in Urumqi using data from two independently sampled cross-sectional surveys conducted in 2012 and 2019. METHODS: The 2012 survey included 1,938 students from Xinshi and Shayibake districts, whereas the 2019 survey included 9,503 students from Xinshi, Shayibake, Tianshan, and Shuimogou districts. Information on visual status and individual and environmental factors was collected. Crude and internally standardised prevalence estimates were calculated. Because the two surveys differed in geographic coverage and sample composition, comparisons between survey years were interpreted descriptively. RESULTS: The crude prevalence of myopia was 39.7% in the 2012 survey and 37.1% in the 2019 survey. After equal-weight standardisation by school stage, the corresponding estimates were 45.9 and 43.7%, respectively. Descriptive prevalence patterns differed across school stages; however, because the two surveys did not have identical geographic coverage or sampling frames, these differences should not be interpreted as evidence of a population-level temporal trend. Myopia was higher in females than males and lower in Han than other ethnic groups (all p < 0.05). Multivariable logistic regression for 2012: risk factors - reading <30 cm from books (OR = 1.51, 95%CI = 1.28-1.78), poor reading/writing habits (OR = 1.55, 95%CI = 1.26-1.91), daily computer use (OR = 1.21, 95%CI = 1.00-1.46), parental myopia (OR = 2.11, 95%CI = 1.65-2.71); protective factors - eye exercises (OR = 0.66, 95%CI = 0.53-0.81), daily outdoor time (OR = 0.84, 95%CI = 0.71-1.00), daily sleep time (OR = 0.75, 95%CI = 0.60-0.95). For 2019: risk factors - reading <30 cm (OR = 1.69, 95%CI = 1.56-1.82), poor habits (OR = 1.22, 95%CI = 1.09-1.36), parental myopia (OR = 2.22, 95%CI = 2.03-2.43); protective factors-resting eyes after 1 h reading/writing (OR = 0.79, 95%CI = 0.74-0.84), eye exercises (OR = 0.87, 95%CI = 0.79-0.95), daily TV hours (OR = 0.85, 95%CI = 0.79-0.92), frequent distance viewing (OR = 0.85, 95%CI = 0.74-0.98), daily outdoor time (OR = 0.90, 95%CI = 0.83-0.98), daily sleep time (OR = 0.84, 95%CI = 0.75-0.94), weekly frequency of eating zhuafan (OR = 0.85, 95%CI = 0.77-0.95). CONCLUSION: Myopia represented a substantial public health burden among schoolchildren in both surveys. Several behavioural and familial characteristics were associated with myopia, although the cross-sectional design precluded causal inference. Because the two surveys used different sampling frames, the observed between-survey differences should not be interpreted as definitive evidence of a temporal change in population prevalence.