Analysis of the factors influencing the treatment zone area after overnight orthokeratology lens wearing

PURPOSE: To identify the influencing factors of the treatment zone area (TZA) after overnight orthokeratology (OK) lens wearing, and validate an integrated open source workflow using R language (R) for measuring treatment zone parameters. METHODS: The retrospective study included 239 children (7-16 years) who wore OK lenses continuously for 12 months. Two OK lens designs were used: 1) Vision Shaping Treatment (VST) lenses, with back optic (BC) zone diameters of 5.5 mm or 6.0 mm; 2) Corneal Refractive Therapy (CRT) lenses, with BC zone diameters of 5.0 mm or 6.0 mm. Patients were divided into four groups based on lens design and BC zone diameter: VST-S (5.5 mm, n = 61), VST-L (6.0 mm, n = 66), CRT-S (5.0 mm, n = 59), and CRT-L (6.0 mm, n = 53). Treatment zone parameters were quantified using R and MATLAB. Spearman correlation analysis and multiple linear regression were applied to explore factors influencing TZA. RESULTS: R and MATLAB showed high agreement in measuring treatment zone parameters: Cronbach's alpha values were 0.993 for treatment zone decentration (TZD) and 0.991 for TZA; intraclass correlation coefficient values were 0.986 for TZD and 0.983 for TZA. TZA, semimajor axis (a), semiminor axis (b), ellipse eccentricity (e), and tilt angle of the fitted ellipses (alpha) were significantly correlated with TZD (P < 0.05). Post hoc comparisons revealed VST-L group had significantly larger TZA than the other three groups (all P < 0.001); TZA of VST-L group was significantly larger than that of CRT-L group (U=719.000, P < 0.001). Corneal mean keratometry change (Δkm), TZD, shape factor change (Δp), preoperative p, and BC zone diameter were independent predictors of TZA (R² = 0.730), with Δkm showing the strongest correlation (Standardized Coefficients = 0.963). CONCLUSION: R is reliable for measurement of treatment zone parameters, with results consistent with MATLAB. The vector of decentration aligned closer with the direction of semiminor axis of the fitted treatment zone ellipse, and greater ellipse eccentricity was associated with greater treatment zone decentration. Δkm, TZD, Δp, preoperative p, and BC zone diameter were independently associated with TZA. These findings characterize factors associated with treatment zone morphology and may inform future prospective studies of individualized orthokeratology lens fitting.