The present study assessed the influence of overnight orthokeratology (ortho-k) on the myopic progression in Korean children and analyzed factors affecting myopic progression.

The ortho-k group was comprised of 31 patients satisfying the inclusion criteria for ortho-k. In the ortho-k group, spherical equivalent refractive error (SER) was measured at baseline, and after 2 weeks, 6 and 12 months. The control group was comprised of 31 patients who were matched according to age, gender, and baseline SER of the ortho-k subjects.

In the ortho-k group, the mean ± SD changes in SER from 2 weeks to 6 months, 6 to 12 months, and 2 weeks to 12 months were -0.17 ± 0.50 D, -0.04 ± 0.76 D, and -0.21 ± 0.78 D, respectively. In the control group, the changes in SER from baseline to 6 months, 6 to 12 months, and baseline to 12 months were -0.38 ± 0.42 D, -0.44 ± 0.38 D, and -0.82 ± 0.68 D, respectively. Significant differences were found between changes in SER from 6 to 12 months and from baseline to 12 months ( p < 0.05). In the ortho-k group, relationships between the changes of SER for 1 year and the numeric values of baseline measurements were analyzed. When comparing the results between the group of SER change ≥ -0.5 D with the group of SER change < -0.5 D, numeric values of white-to-white diameters of the 2 groups were different, and a significant correlation was found between the range of SER change and the white-to-white diameter (Pearson's r = -0.471, p = 0.008).

Ortho-k is effective for slowing myopic progression. The smaller the white-to-white diameter, the slower the myopic progression could be.