The Effect of Relative Corneal Refractive Power Shift Distribution on Axial Length Growth in Myopic Children Undergoing Orthokeratology Treatment.

Purpose: To quantify the spatial distribution of relative corneal refractive power shift (RCRPS) to investigate its association with axial length growth.
Methods: Eighty myopic children were randomly assigned for fitting with type A or B lenses. Axial lengths and corneal topographies were measured at baseline and the 1-, 6-, and 12-months follow-up visits. Treatment-zone decentrations and sizes were derived from tangential maps. RCRPSs were computed by taking the difference between after-treatment and baseline axial maps and then subtracting the apex value. Values at the same radius were averaged to obtain an RCRPS profile, from which four distributional parameters were extracted: the peak value (Rmax), the location where the profile first reached its half peak (X50), and the powers summed within 4- and 8-mm diameter areas (Sum4 and Sum8, respectively). Linear mixed models were used to analyse the correlation between the AL growth and the distributional parameters.
Results: At baseline, no significant differences were observed between the two groups. After treatment, Axial length growth was significantly smaller in subjects fitted with type-B lenses (0.15 ± 0.16 vs 0.25 ± 0.22 mm, P = .028). Smaller treatment-zones (1.56 ± 0.14 vs 1.75 ± 0.13 mm, P < .01), smaller X50 values (1.56 ± 0.39 vs 1.98 ± 0.28 mm, P < .01), and greater Sum4 values (11.83 ± 6.47 vs 8.14 ± 5.06 D, P = .01) were also observed in subjects wearing type-B lenses. Among the distributional parameters, only X50 was significantly associated with AL growth in the multiple regression analysis ( P = .005).
Conclusion: The spatial distribution of RCRPS is critical in retarding AL growth, and the ones reaching peak within a shorter distance from the apex may provide better myopia control.