Relationship between axial length and spherical equivalent refraction in Chinese children

Purpose: To evaluate the relationship between axial length (AL) and spherical equivalent refraction (SER) in Chinese children. Methods: This hospital-based cross-sectional study included 1208 eyes (from 617 Chinese boys and 591 Chinese girls), ranging between 2 and 12 years. All subjects were divided into subgroups according to the spherical equivalent refraction (SER) (hyperopia, emmetropia, and myopia) and age (2-6 years, 7-9 years, and 10-12 years). Comparisons were made between age, sex, and SER groups. Multiple linear regression analysis was used to evaluate the correlation of AL and SER for all groups. Results: The mean AL and SER were significantly different among the three age groups: 2-6 years group (AL: 22.24 f 1.59 mm; SER: 0.73 f 2.67 D); 7-9 years group (AL: 23.49 f 1.10 mm; SE:-0.68 f 1.97 D) and 10-12 years group (AL: 24.33 f 1.02 mm; SER:-1.72 f 1.86 D). Boys showed longer AL compared with the girls (23.66 f 1.51 mm vs 23.05 f 1.32 mm). However, as for SER, the girls (-0.70 f 2.17 D) showed smaller SER (more myopia) compared with the boys (-0.4 f 2.48 D). After adjusting for age and sex, the SER tended to decrease (became more myopic) 1.23 D (95% CI: 1.15-1.30D) with a 1 mm increase of AL. Among the different SER groups, the SER tended to become more myopic per mm of AL by 1.09 D (95% CI: 0.97-1.21D) for the myopia group, 1.38 D (95% CI: 1.23-1.54 D) for the hyperopia group, and 0.05 D (95% CI: 0.02-0.08 D) for the emmetropic group. In addition, an increase of 1 mm elongation of AL showed a decrease of SER by 1.05 D (95% CI: 0.90-1.20 D) among 2 - 6-year-olds, by 1.40 D (95% CI: 1.30-1.51 D) among 7 - 9-year-olds, and by 1.37 D (95% CI: 1.21-1.52 D) among 10-12-year-olds. As for sexual differences, the girls 1.68 D, (95% CI: 1.57-1.79 D) showed a more significant myopic shift of SER with a 1 mm increase of AL compared with the boys (0.94 D, 95% CI: 0.84-1.04 D). Conclusions: Our results indicated a strong linear relationship between SER and AL and an early-rising trend of myopia in Chinese children.