Purpose <p>To identify the potential biometric risk factors for the onset of myopia in emmetropic school-age children.</p> Study design <p>Longitudinal study.</p> Methods <p>First, we performed a preliminary study in which objective refraction, corneal refractive power, higher-order aberrations (HOAs), and axial length (AL) was measured annually in 98 Grade-3 (age 8) elementary schoolchildren over a 4-year period from 2006 to 2009. We also examined the refractive changes over 3 years, and assessed the correlation between those changes and the baseline data. Based on those findings, we performed the primary study in which objective and subjective refraction, corneal refractive power, HOAs, and AL was measured annually in Grade 1 (age 6) through Grade 8 (age 13) schoolchildren from 2013 to 2022. We investigated the risk factors for AL elongation over 1 year in children with emmetropia at the first year using a multivariable linear mixed model.</p> Results <p>Findings in the preliminary study revealed that AL in the first year (age 8) had the strongest correlation with myopia progression for 3 years. The risk factors for AL elongation among emmetropia were 1) lower grade, 2) sex (female), 3) myopic objective refraction (spherical equivalent), 4) longer AL (mm), 5) lower corneal coma-like aberration (CA) at the pupil diameter of 6 mm, and 6) higher ocular spherical aberration (SA) of 4 mm and lower ocular SA at the pupil diameter of 6 mm in the primary study.</p> Conclusion <p>Risk factors for myopia onset in emmetropic school-age children include AL, refraction, corneal CAs, and ocular SAs.</p>