A Novel Model for Cornea Power Shift in Eyes Wearing Orthokeratology Lenses With Different Back Optic Zone Diameters for Myopia Control

PURPOSE: The purpose of this study was to quantify the corneal power changes after wearing orthokeratology lenses of different back optic zone diameters (BOZDs) and to propose a novel 4-parameter model capable of revealing the associations between each parameter and axial length growth (ALG).

METHODS: A prospective self-controlled study was conducted between June 2022 and December 2023. One eye in each subject (N = 33) was randomly assigned to wear a lens with a BOZD of either 5 mm (5 oz) or 6 mm (6 oz). Axial lengths were measured at 6 and 12 months and ALG was calculated from those measurements. Corneal topography obtained at baseline, 6 months, and 12 months after lens-wearing was analyzed, and the central flatten region is considered as the treatment zone (TZ). The power change profile was fitted with a riverbank model with parameters describing the amplitude, location shift, slope, and base. A linear mixed model was used to evaluate the association between ALG and model parameters.

RESULTS: ALG was significantly slower in eyes wearing 5 oz lenses (0.19 ± 0.15 vs. 0.26 ± 0.15 mm, P < 0.01). TZ sizes were smaller in the 5 oz group (6.76 ± 2.21 vs. 8.07 ± 2.01 mm2, P < 0.01). For relative corneal refractive powers shift (RCRPS) profiles averaged across 360 degrees, greater amplitudes (4.70 ± 1.05 vs. 4.33 ± 0.99 diopter [D], P = 0.04) and smaller location shifts (1.97 ± 0.32 vs. 2.11 ± 0.27 mm, P < 0.01) were found in the 5 oz group. For RCRPS profiles calculated in eight different meridians, strong meridional modulations were found in the parameters in each group. Moreover, significant inter-group parameter differences (P < 0.01) were only found on the temporal side. Multiple regression showed that only location shift was significantly associated with ALG (P = 0.01).

CONCLUSIONS: Eyes wearing a 5 oz lens had significantly slower ALG, compared with the eyes wearing 6 oz lens. Such difference may be attributed to the smaller location shift on the temporal side.