Distribution of axial length in Australians of different age groups, ethnicities, and refractive errors

Abstract

Purpose : Although longer axial length (AL) is associated with myopia, there is little information on the distribution of AL. We reported the AL distributions of Australians aged 5-89 years with different refractive errors.

Methods : We retrospectively analyzed spherical equivalent (SE) and AL data of 5211 participants from 8 Australian studies. All participants underwent an eye examination including ocular biometry and cycloplegic autorefraction. Participants were classified into hyperopes (SE > +0.50 D; n=1526), emmetropes (SE +0.50 D to >-0.50 D; n=2198) and myopes (SE ≤-0.50 D, n=1487). A non-linear piecewise regression model adjusted for age, sex, and ethnicity (European, European-Polynesian, East Asian, South Asian, and other/mixed) was used to analyze the association between age and AL. The regression slopes were obtained for 784 participants below 18 years and 4427 participants 18 years or older. These results were compared with longitudinal data from the Raine Study Gen2 where the AL was measured at the ages of 20 (baseline) and 28 years.

Results : The median AL was 23.12 mm (IQR= 22.62 to 23.64) in hyperopes; 23.38 mm (IQR= 22.84 to 23.90) in emmetropes; and 23.91 mm (IQR=23.26 to 24.78) in myopes. After adjustments, females had shorter AL by 0.54 mm (95% CI: 0.59 to 0.50) compared to males (p<0.001), and while East Asians and those of other/mixed ancestry had longer AL by 0.55 mm (95% CI: 0.33 to 0.77; p<0.001) and 0.38 mm (95% CI: 0.16 to 0.58; p<0.001) compared to Europeans. A piecewise regression showed that until 18 years of age, the AL was longer by 0.016 mm in hyperopes (p=0.058), 0.052 mm in emmetropes (p<0.001), and 0.125 mm in myopes (p<0.001) per year increase in age. After 18 years, the AL was longer by 0.003 mm in hyperopes (p<0.05), 0.004 mm in emmetropes (p<0.05), and 0.012 mm in myopes (p<0.001) per year increase in age. The longitudinal data from the Raine study Gen2 revealed that those with myopia at baseline had a significant change in the SE and AL by -0.16 D (p<0.001) and 0.57 mm (p=0.01) per year compared to emmetropes.

Conclusions : This cross-sectional data suggests there is a minimal increase in AL in non-myopic eyes beyond 18 years of age. The association between age and AL in myopic eyes was greater in both childhood and adulthood compared to non-myopic eyes. Further longitudinal studies in AL covering a large age range are required to guide myopia interventions.

This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.