Longitudinal change in components of astigmatism and its association with axial length-corneal radius ratio in Chinese young children: the Nanjing Eye Study

To assess the longitudinal change in components of astigmatism from age 4 to 7 years and its association with axial length-corneal radius ratio (AL/CR). Children born between September 2011 and August 2012 in Yuhuatai District of Nanjing were invited to participate in the Nanjing Eye Study for a comprehensive eye examination annually since 2015. The data presented in this paper were obtained in 2016, 2017, and 2019. At each study encounter, noncycloplegic autorefraction and ocular biometric parameters were measured. Changes of total astigmatism (TA), corneal astigmatism (CA), anterior corneal astigmatism (ACA), residual astigmatism (RA), and internal astigmatism (IA) were analyzed in clinical notation (Cyl) and vector notation (J0, J45). Nine hundred fifty-four children (mean ± standard deviation of baseline age: 4.63 ± 0.29 years, 53.7% boys) had complete data and were included in this study. Mean slopes of longitudinal changes in Cyl notation were significantly negative for TA, CA, and ACA, but positive for IA. TA, CA, ACA, and RA of J0 notation had a shift toward increasing with-the-rule (WTR) astigmatism and/or decreasing against-the-rule (ATR) astigmatism. TA of J45 notation showed an increase in astigmatism at axis 135° and/or a decrease in astigmatism at axis 45°, while CA and ACA of J45 notation showed an opposite change. Longitudinal changes in ACA and IA were negatively correlated in J0 notation, but not in J45 notation. Based on compensation factor (CF, defined as the minus ratio of IA and ACA), the compensation proportions for J0 in varying degrees (CF: 0.1–2) in 2016, 2017, and 2019 were 91.3%, 93.5%, and 90.0%, respectively, while these for J45 were 74.9%, 76.5%, and 34.6%, respectively. Higher AL/CR increase was associated with less decrease or more increase in CA and ACA of Cyl notation, and a shift toward increasing WTR and/or decreasing ATR in these of J0 notation. The compensatory role of IA was persistent and prominent from 4 to 7 years old for J0 notation in Chinese young children. The progression of AL/CR was correlated with astigmatism originated from the cornea.