Variabilty of the Axial Length Contribution to Refraction by Childhood Age and Ethnicity

Abstract

Purpose:: To evaluate the relationship between ocular biometric parameters (axial length, corneal radius, etc) and refraction in a cross-sectional population-based sample of Australian school children.

Methods:: High school children in the Sydney Myopia Study, predominantly aged 12 years (n=2353, 75.3% response), participated in ophthalmic examinations including cycloplegic autorefraction (1% cyclopentolate) and ocular biometry (IOLMaster). Socio-demographic data including ethnicity were derived from questionnaires completed by parents. Linear regression analyses using ocular biometric parameters as explanatory variables and spherical equivalent as the outcome variable were performed for the whole sample, and for European Caucasian and East Asian subgroups separately.

Results:: Axial length was significantly correlated with spherical equivalent (correlation coefficient, r=-0.61, p<0.0001) in 12-year old children. In multivariate models that adjusted for age, gender and ethnicity, axial length accounted for 37% of the variability in spherical equivalent for all children, including 24% for children with European Caucasian ethnicity and 65% for children with East Asian ethnicity. The correlation of spherical equivalent with corneal radius or lens power was low (all r<0.20). Analyses for 6-year old children showed that axial length explained only 19% of the variability in spherical equivalent after adjusting for age, gender and ethnicity; with lower proportions in the European Caucasian (18%) and East Asian subgroups (12%).

Conclusions:: In this sample of over 4,000 school children, the correlation between axial length and spherical equivalent refraction increased substantially from 6 to 12 years of age, and was a more predominant determinant of refraction in children of East Asian ethnicity than in children of European Caucasian ethnicity.

Keywords: myopia • refractive error development • emmetropization