Longitudinal Changes in Peripheral Refraction, Lag and Axial Length in Myopic Children Treated with Orthokeratology: A 12-Month Prospective Study

Background/Objectives: High accommodative lag and relative peripheral hyperopic defocus during near work have been proposed as potential contributors to myopia progression. Orthokeratology (OK) reshapes the cornea to provide central correction while inducing peripheral myopic defocus. This prospective 12-month study aimed to evaluate longitudinal changes in peripheral refraction, accommodative lag, and axial length (AL) in myopic children treated with OK. Methods: Children aged 7 to 17 years with low-to-moderate myopia were fitted with spherical (CRT™ STD) or toric (CRT™ DA) OK lenses and followed for 12 months. Horizontal peripheral refraction (vector M, J0, J45) up to ±30°, accommodative lag and non-cycloplegic AL were measured. Results: Forty-seven participants completed the study. Mean AL increased from 24.76 ± 0.87 mm at baseline to 24.86 ±0.85 mm at 12 months (p < 0.001). OK induced a stable, symmetrical redistribution of relative peripheral myopic defocus across visits. The toric design showed more consistent significant variations in the J0 astigmatic component across eccentricities. No significant correlations were found between AL elongation and changes in peripheral refraction (p = 0.194) or accommodative lag (p > 0.05) in the overall sample. However, subjects in the lag variation group showed significant AL increases (p < 0.05), while those in the no lag variation group did not (p > 0.05). Conclusions: OK consistently induces a stable pattern of peripheral myopic defocus. While peripheral defocus and accommodative lag do not linearly correlate with global axial growth, accommodative behavior may be associated with individual differences in axial growth. Biometry remains important for monitoring treatment outcomes.