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

Purpose: To evaluate time trends of axial length (AL) in 4 and 5 year-olds children, and to assess factors associated with AL in Shanghai from 2013 to 2019.

Methods: This was a 7-year observational study of children of 4 and 5 year-olds in Shanghai. AL, horizontal and vertical corneal curvature, spherical equivalent (SE), body height and weight were measured. Furthermore, a questionnaire was collected including time outdoors and bad habits of using eyes.

Results: No significant differences were found in AL (P = 0.526) in 4 year-olds children, whereas 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. No significant differences were found in AL (P = 0.304), SE (P = 0.200) and weight (P = 0.292) in 5 year-olds children, whereas 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 associated significantly with boys (P < 0.001) and time outdoors (P < 0.001) in all the 4 year-olds children, with boys (P < 0.001) and time outdoors (P = 0.014) in all the 5 year-olds children.

Conclusions: ALs of 4 and 5 year-olds children remain relatively stable in Shanghai from 2013 to 2019. Longitudinal studies are needed to confirm the relationship between AL elongation and environmental risk factors.