This study evaluates the effects of a modest reduction in back optic zone diameter (BOZD) in orthokeratology (ortho-k) lenses on axial elongation and visual performance. The goal is to determine whether this adjustment enhances myopia control in children with rapid progression and suboptimal outcomes, while maintaining visual quality and exploring the underlying mechanisms.This retrospective study analyzed data from 109 myopic children undergoing ortho-k fitting over two years. The continued group wore traditional 6.0 mm BOZD lenses, while the switched group wore 6.0 mm lenses in the first year and transitioned to 5.8 mm BOZD lenses in the second year. The changes of Axial length (AL) elongation and corneal topography parameters, including treatment zone (TZ) size, cumulative relative corneal refractive power within a 4.80 mm diameter (Sum4.8), TZ decentration, and percentage of defocus zone within the pupil area (PDZP).In the continued and switched groups, the baseline age was 9.92 ± 2.19 and 9.38 ± 1.58 years, respectively. During the second year, the switched group exhibited a significantly reduced AL elongation compared to the continued group (0.17 ± 0.24 mm vs 0.28 ± 0.17 mm, p = 0.02). Additionally, Sum4.8 was significantly elevated in the continued group. However, there wasno significant differences in TZ size and decentration, or PDZP between the two groups, indicating that the 0.2 mm reduction in BOZD may not be sufficient to influence these parameters.The transition to a BOZD of 5.8 mm improved myopia management by mitigating AL elongation without producing visual problems, possibly attributable to an augmented peripheral myopic defocus. This study offers empirical support for the clinical advantages of decreasing BOZD in ortho-k for pediatric patients with suboptimal myopia control.Copyright © 2025. Published by Elsevier Ltd.