Differences in ocular biometry between urban and rural children matched by refractive error: the Shandong Children Eye Study

To determine the differences in mean ocular dimensions between urban and rural children and identify possible influencing factors.This work uses previously published data from the Shandong Children Eye Study, which was based on a random cluster sampling applied to a cross-sectional school-based study design in the rural Guanxian County and Weihai city. All children underwent auto-refractometry and biometry under cycloplegia.The study included 3290 children (aged 9.35 ± 2.93 years), consisting of 888 pairs of boys and 757 pairs of girls matched by sex, age and refractive error (each pair matching one child from urban cohort with one from the rural cohort). Overall urban children were significantly taller and heavier than rural children (t-test; p < 0.001), which was confirmed for all age groups for weight. Urban ocular axial lengths were significantly longer by 0.23 mm compared to the rural population (t-test; p < 0.001), mostly in younger children and boys. Meanwhile, corneal curvatures were flatter in the urban cohort by 0.08 mm (p < 0.001). This association of axial length with urban vs rural region was reduced in magnitude by 69.7% after accounting for height.For the same, matched refractive error, children from urban regions had significantly longer eyes and flatter corneal curvature than rural children. Since corneal curvature is defined during the first 2 years of life, early environmental factors may be the source of these differences in ocular dimensions.