Longitudinal Relationship between Axial Length and Height in Chinese Children: Guangzhou Twin Eye Study.

PURPOSE To understand the growth model of axial length (AL) and height, and to explore the relationship between the two with the passage of time. METHODS We followed twins in the Guangzhou Twin Eye Study for five years. The AL of both eyes was measured by partial coherence interferometry, and height was measured by a standard scale during each visit. A multivariate multilevel mixed model was adopted for data analysis. RESULTS A total of 1217 children were included in the study. Both AL and height increased, but the rate of growth slowed down with age. The mitigation rate of height growth was -0.34 cm/year; while that of AL growth was -0.01 mm/year. AL was positively related to height, with a relevant coefficient of R = 0.22 (Cov [height intercept, AL intercept] = 1.56, 95% CI = 1.14 to 1.99). The growth rates of AL and height were also positively related, with a relevant coefficient of R=0.18 (Cov [height slope, AL slope] = 0.03, 95% CI = 0.01 to 0.05). However, taller children had slower rates of height increases, with a relevant coefficient of R = -0.12 (Cov [height intercept, height slope] = -1.33, 95% CI = -2.25 to -0.42); but had faster AL growth, with a relevant coefficient of R = (Cov [height intercept, AL slope] = 0.02, 95% CI = -0.05 to 0.08, R = 0.02). AL and its growth rate were positively related to each other, with a relevant coefficient of R = (Cov [AL intercept, AL slope] = 0.04, 95%CI = 0.03 to 0.05, R = 0.3); while the growth rates of AL and height were negatively related to each other, with a relevant coefficient of R = (Cov [AL intercept, height slope] = -0.03 95%CI = -0.16 to 0.1, R = -0.02). CONCLUSION The increase in children's AL is relevant to their height increases. The faster their height increases, the faster their AL increases.