Effects of Orthokeratology Lens Decentration Induced by Paracentral Corneal Asymmetry on Axial Length Elongation

Background: To determine the influence of the magnitude of treatment zone decentration on axial length (AL) elongation and to investigate the association between paracentral corneal asymmetry and orthokeratology (OK) lens decentration. Methods: This retrospective study involved 268 subjects (7–14 years) who wore OK lenses for one year. The parameters that reflected the paracentral corneal asymmetry were recorded: corneal toricity; Q value; anterior corneal curvature; and elevation values at the 6-, 7-, and 8-mm chords along the horizontal meridian. The relationships between these data and the amount of treatment zone decentration were analyzed. The relationship of the decentration magnitude and AL elongation was also analyzed. Results: AL elongation was significantly associated with initial age, baseline spherical equivalent, AL, and the decentration magnitude. The subjects with large decentration magnitude showed less AL elongation. The decentration was affected by corneal morphology at the 8-mm chord on the nasal side. In the low curvature group (≤41.0D), the decentration magnitude had a stronger correlation with AL elongation than in all subjects. In the high curvature group (>41.0D), the decentration magnitude was no longer correlated with the AL elongation. Conclusion: The decentration of the OK lens effectively slowed the elongation of the eyeball. When the nasal curvature was less than 41.0 D at the 8-mm chord, the magnitude of decentration was predetermined by the flatter curve.