Nomogram to predict the axial elongation with orthokeratology: A 6-year follow up study

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PURPOSE: To develop and validate a nomogram model for predicting axial elongation in children with myopia undergoing orthokeratology (ortho-k) treatment. METHODS: A cohort of 111 myopic children who received ortho-k between 2014 and 2016 and consistently wore lenses for at least 6 years was analyzed. Right eyes were used as the model group, left eyes as the validation group. Demographic and ocular parameters were collected. A multivariable logistic regression was applied to model group data to construct the nomogram. Discriminative ability was assessed using the concordance index (C-index), calibration plots, and decision curve analysis (DCA). Statistical analysis was conducted in R version 4.2.3, with p ≤ 0.05 considered significant. RESULTS: Mean axial elongation in the first year was 0.14 mm (95 % CI: 0.12-0.17 mm); total elongation over six years was 0.83 mm (95 % CI: 0.75-0.91 mm). After adjusting for multicollinearity, age (β = -0.134, p < 0.001), gender (β = -0.226, p = 0.011; males as reference), baseline axial length (β = 0.950, p < 0.001), and first-year axial elongation (β = 1.714, p < 0.001) were independently associated with axial length after six years. The model yielded a C-index of 0.93 (95 % CI: 0.88-0.99) in the model group and 0.80 (95 % CI: 0.80-0.96) in the validation group. DCA showed clinical benefit. CONCLUSIONS: Ortho-k effectively slowed axial elongation over six years. The nomogram reliably predicts whether axial length will exceed 26.0 mm after long-term ortho-k treatment.