Generational Difference of Axial Length and Its Risk Factors in Urban and Rural China

PURPOSE: To compare the axial length difference (ALD) and the estimated generational axial length shift (ALS) from parents to their children and its risk factors in urban and rural China. METHODS: Participants were enrolled from two longitudinal cohort studies, the Beijing Myopia Progression Study (BMPS) and the Handan Offspring Myopia Study (HOMS). Ocular biometry was performed in both parents and their children. ALD was defined as the difference between the children's axial length and the corresponding parental axial length. Generational ALS was estimated according to a binominal prediction model at 18 years of age. RESULTS: 237 and 380 urban and rural Chinese children (6–17 years) and their parents from the BMPS and HOMS, respectively, were enrolled. Children's axial length was estimated to be closest to the parental axial length at 11 and 9 years of age in the urban and rural areas, respectively; the estimated generational ALS would be 1.53 and 0.57 mm, respectively. Multivariable regression analysis revealed that older children (urban β = 0.26, p < 0.001; rural β = 0.11, p < 0.001) and males had larger ALD (urban β = 0.55, p < 0.001; rural β = 0.52, p < 0.001) in both areas. Furthermore, urban children with more educated parents (fathers: β = −0.30, p=0.002; mothers: β = −0.29, p=0.004) and more outdoor activity (β = −0.23, p=0.006) had a less ALD. CONCLUSIONS: The urban generational axial length shift was estimated to be approximately 1 mm longer than that of the rural area. These results suggest different environmental effects on the ocular development in these two populations of Chinese children.