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

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).

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.

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).

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.