Time trend of axial length and associated factors in 4- and 5-year-old children in Shanghai from 2013 to 2019

PURPOSE: To evaluate the time trend of axial length (AL) and associated factors in 4- and 5-year-old children in Shanghai from 2013 to 2019. METHODS: This was a 7-year observational study of 985 four-year-old and 1059 five-year-old children in Shanghai. AL, horizontal and vertical corneal curvature, spherical equivalent (SE), and body height and weight were measured. Furthermore, a questionnaire was collected, including time outdoors and bad eyesight habits. RESULTS: In 4-year-old children, no significant difference was found in AL (P = 0.526), but significant differences were observed in SE (P = 0.001), horizontal corneal curvature (P = 0.006), vertical corneal curvature (P = 0.004), height (P < 0.001), and weight (P = 0.022) from 2013 to 2019. In 5-year-old children, no significant differences were found in AL (P = 0.304), SE (P = 0.200), or weight (P = 0.292), but significant differences were observed in horizontal corneal curvature (P = 0.040), vertical corneal curvature (P = 0.015), and height (P < 0.001) from 2013 to 2019. Multivariate analyses revealed that AL was mainly significantly associated with boys and time outdoors in the 4- and 5-year-old children. CONCLUSIONS: The AL of 4- and 5-year-old children remained relatively stable in Shanghai from 2013 to 2019. Longitudinal studies are needed to confirm the relationship between AL elongation and environmental risk factors.