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.