Long-Term Effect of Overnight Orthokeratology on Axial Length Elongation in Childhood Myopia: A 5-Year Follow-Up Study

PURPOSE: Our prospective study was conducted to compare axial length elongation in myopic children receiving long-term overnight orthokeratology (OK) treatment to those wearing spectacles as controls. METHODS: There were 59 subjects enrolled in this study. The OK group comprised 29 subjects who matched the inclusion criteria for OK. The control group comprised 30 subjects who also matched the inclusion criteria for OK, but preferred spectacles for myopia correction. Axial length was measured periodically for 5 years using an IOLMaster device, and the time course of changes was evaluated and compared between the groups. RESULTS: A total of 43 subjects (22 and 21 in the OK and control groups, respectively) completed the 5-year follow-up examinations. At baseline, the mean age ± SD was 10.04 ± 1.43 and 9.95 ± 1.59 years, the spherical equivalent refractive error was -1.89 ± 0.82 and -1.83 ± 1.06 diopters (D), and the axial length was 24.09 ± 0.77 and 24.22 ± 0.71 mm in the OK and control groups, respectively, with no significant differences between the groups. The increase in axial length during the 5-year study period was 0.99 ± 0.47 and 1.41 ± 0.68 mm for the OK and control groups, respectively, and the difference was statistically significant (P = 0.0236, unpaired t-test). The annual increases in axial length were significantly different between the groups for the first (P = 0.0002), second (P = 0.0476), and third years (P = 0.0385), but not for the fourth (P = 0.0938) and fifth (P = 0.8633) years. There were no severe complications throughout the study period. CONCLUSIONS: The current 5-year follow-up study indicated that OK can suppress axial length elongation in childhood myopia.