Age-dependent Distribution of Astigmatism and its Component in Chinese Preschool Children

Abstract

Background: There is an compensatory effect between corneal astigmatism (CA) and internal astigmatism (IA). And the refractive astigmatism (RA) decreased fast in the early 3 years. Nevertheless, little attention was paid to the change in astigmatism in preschool children. Thus, we aimed to investigate the age-dependent distribution of astigmatism and its component in Chinese preschool children from year 3 to year 6 and also, to study the relationship between ocular biometry and IA. Methods: Automated refraction, keratometry and axial length (AL) were performed in this cross-sectional study. The IA was determined as the vector difference between RA and CA. The magnitude and type (with-the-rule WTR, against-the-rule ATR, oblique) of RA, CA and IA were investigated according to the age. Spearman correlation was adopted to detect the factors that may influence IA. Results: A total of 2315 subjects (2315 right eyes) (47.38% female) with a mean age of 4.52±0.88 years (range 3-6 years) were included. The magnitude and the ratio of three kinds of CA components did not change with aging (p=0.1233 and p>0.1, respectively). Though the axial distribution of RA remained unchanged with aging, a significant reduction in RA was seen in year 6 compared to that of year 3 and year 4 (p=0.036 and 0.041, respectively). Conversely，the ATR component in IA was lower in year 6 (68.02%) than it in year 3 (81.92%) and year 4 (77.12%) (both p<0.001) accompanied by increased frequency of oblique astigmatism in year 6 than it in year 3 and year 4 (p<0.001 and p=0.012,respectively). Negative relationship was found between IA and AL. Conclusion: RA decreased from year 3 to year 6. The shift of the axis in IA from ATR to Oblique and WTR may account for the reduction in RA. Eyes with shorter AL had larger IA. Keywords: Internal astigmatism; corneal astigmatism; axial length; with-the-rule.

The Distribution Pattern of Ocular Residual Astigmatism in Chinese Myopic Patients

“…Another scenario where ORA may be affected is the malposition of the crystalline lens, such as lens subluxation and ectopia lentis ( 40 ). A recent study also showed that the ORA was greater in a population with shorter axial length and larger lens thickness, as internal astigmatism mostly arose from surfaces of the crystalline lens ( 41 ).…”