The relationship between baseline axial length and axial elongation in myopic children undergoing orthokeratology

PURPOSE: To investigate the correlation between the baseline axial length (AL) and axial elongation in myopes undergoing orthokeratology (ortho‐k). METHODS: This was a retrospective study. During the 1‐year follow‐up, 1176 children (aged 8–14 years) were included and divided into an ortho‐k group (n = 588) and a single‐vision spectacle group (n = 588). The ortho‐k group participants (8–11 years of age) who completed the 3‐year follow‐up (n = 150) were further divided into three subgroups stratified by their baseline AL: subgroup 1 (AL < 24.5 mm), subgroup 2 (24.5 ≤ AL < 26 mm) and subgroup 3 (AL ≥ 26 mm). AL was measured at baseline and during the annual visit. RESULTS: The ortho‐k group exhibited slower 1‐year axial elongation (39% reduction) than the spectacle group. The 1‐year axial elongation was negatively correlated with initial age in both groups. A negative association between 1‐year axial elongation and baseline AL was observed in the ortho‐k group but not in the spectacle group. However, this relationship only existed in ortho‐k participants 8–11 years of age. For the younger ortho‐k participants who completed the 3‐year follow‐up, the annual axial elongation was significantly higher in subgroup 1 for the first and second years but not in the third year compared with subgroups 2 and 3. CONCLUSION: Axial elongation was negatively correlated with baseline AL in the ortho‐k group. Children aged 8–11 years with longer baseline AL (≥24.5 mm) demonstrated slower annual axial elongation during the first 2 years of ortho‐k treatment, which may provide insight into establishing individual guidelines for controlling myopia using ortho‐k in children with different baseline characteristics.