Real axial length (RAL): a novel choroid-inclusive metric for myopia management

To introduce and validate the real axial length (RAL)-the distance from the corneal vertex to the posterior choroidal surface measured by swept-source OCT angiography (OCTA). RAL aims to reduce the influence of choroidal thickness on conventional axial length (AL) measurements. The study also compared OCTA-derived parameters with those from the IOL Master 700 to confirm measurement accuracy and established age-specific RAL references in children and adolescents without myopia. This cross-sectional study enrolled Chinese children with normal uncorrected vision. VG 200D and IOL Master700 were used to measure AL, central corneal thickness (CCT), anterior chamber depth (ACD), aqueous depth (AQD), and lens thickness (LT). VG 200D additionally provided new AL parameter - RAL. The intraclass correlation coefficient (ICC) and Bland-Altman analysis were applied to assess device concordance in general parameter. Subsequently, VG 200D-derived RAL values were analyzed across age groups. Of 1833 participants aged 5-17 years (909 males, 924 females) were enrolled. The mean RAL was 24.04 mm and the mean AL was 23.52 mm, showing a statistically significant difference (p < 0.001), measured by VG 200D. AL were 23.49 ± 0.99 mm and 23.52 ± 1.02 mm respectively in Master 700 and VG 200D, showed good agreement (ICC = 0.956). At age 5, boys exhibited a significantly shorter RAL than girls, with median values of 23.55 mm (interquartile range, IQR: 22.91-23.76 mm) and 22.32 mm (IQR: 21.99-23.15 mm), respectively (p = 0.04). By age 17, the RAL increased to 25.26 mm (IQR: 24.75།25.64 mm) in boys and 25.24 mm (IQR: 24.49།25.81 mm) in girls, showing no significant sex difference (p = 0.73). RAL exceeded AL by approximately 0.5 mm. The VG 200D demonstrated strong agreement with IOL Master 700 for standard biometric parameters. The difference in RAL length between boys and girls may progressively narrow with increasing age. RAL may offer a valuable tool for objectively evaluating true ocular growth and myopia control efficacy.