Axial Length/Corneal Radius of Curvature Ratio and Myopia in 3-Year-Old Children

This study investigated the association of axial length (AL) to corneal radius of curvature (CRC) ratio with spherical equivalent (SE) in a 3-year old Asian cohort. Three-hundred forty-nine 3-year old Asian children from The Growing Up in Singapore towards Healthy Outcomes (GUSTO) birth cohort study underwent AL and CRC measurements with a noncontact ocular biometer and cycloplegic refraction using an autorefractor. The ratio of AL to CRC (AL/CRC) was calculated for all the participants, and subsequently AL, CRC, and AL/CRC were analyzed in relationship to SE. The SE showed better correlation with AL/CRC (Spearman's correlation coefficient, ρ = -0.53; 95% confidence interval [CI]: -0.66; -0.49; < 0.001) compared to either AL or CRC alone ([ρ = -0.36; 95% CI: -0.51 to 0.51; = 0.01] and [ρ = 0.05; 95% CI: -0.04 to 0.17; = 0.34], respectively). Mean AL/CRC was 2.91 ± 0.06 among myopes and decreased to 2.79 ± 0.06 among hyperopes. Axial length to corneal radius of curvature was strongly correlated with SE in myopes (ρ = -0.78; 95% CI: -3.76; -0.79; = < 0.001), but not in emmetropes and hyperopes ([ρ = -0.39; 95% CI: -10.73; -0.57; = 0.01] and [ρ = -0.18; 95% CI: -17.28; 12.42; = 0.38], respectively). Linear regression adjusted for gender and ethnicity showed a 0.74-diopter shift in SE towards myopia with every 0.1 increase in AL/CRC ratio ( < 0.001, = 0.33). The correlation between SE and AL/CRC is stronger than that between AL or CRC alone. This suggests that in a research setting, when cycloplegic refraction is difficult to perform on 3-year-old children, AL/CRC may be the next best reference for refractive error. In the research setting, AL/CRC may be the next best reference for refractive error over AL alone when cycloplegic refraction is unavailable in 3-year old children.