Longitudinal rebalancing of axial length asymmetry in anisometropic children under orthokeratology: a large-scale cohort study.

PURPOSE: To characterize longitudinal changes in axial length (AL) in anisometropic children undergoing orthokeratology, focusing on eye-specific elongation and change in inter-ocular AL difference (IALD).

METHODS

This retrospective longitudinal study included 79,409 visits from 9,978 orthokeratology-treated children (8,133 isometropic, 1,845 anisometropic). Propensity score-matched (PSM) subsets were constructed for the more-myopic (PSM1, n = 3,682) and less-myopic eyes (PSM2, n = 2,326). Linear mixed-effects models based on the full cohort estimated AL changes and their associations with baseline inter-ocular spherical equivalent refraction (SER) difference, adjusting for age, gender, axial length, and corneal curvature.

RESULTS

After matching, anisometropic children exhibited modestly slower axial elongation than isometropic controls in both eyes (more-myopic: 0.093 ± 0.156 vs. 0.110 ± 0.158 mm/year; less-myopic: 0.133 ± 0.156 vs. 0.146 ± 0.161 mm/year; both P < 0.05). Linear mixed‑effects models revealed a dose‑dependent rebalancing effect: each 1‑D increase in baseline inter‑ocular SER difference was associated with 0.020  mm less annual elongation in the more‑myopic eye and 0.016  mm more in the less‑myopic eye (both P < 0.001), leading to a faster reduction in IALD (β =  - 0.036  mm/year per D; P < 0.001). Younger age and a smaller initial IALD predicted successful isometropic conversion (defined as achieving an IALD < 0.4 mm), a group which exhibited markedly faster IALD reduction than those with persistent anisometropia (-0.081 vs. - 0.030 mm/year; P < 0.001).

CONCLUSIONS

In anisometropic children undergoing orthokeratology, greater baseline anisometropia was associated with an asymmetric pattern of axial growth, characterised by stronger suppression in the more-myopic eye and comparatively less suppression in the less-myopic eye. This anisometropia-dependent modulation was associated with an accelerated reduction in the inter‑ocular AL difference, suggesting that orthokeratology facilitates progressive inter‑ocular convergence in children with higher baseline anisometropia. The treatment-driven heterogeneity and age-dependent sensitivity highlight a critical window for early clinical intervention.