Sample size
SVS
Based on previous findings, we anticipated a mean (SD) AL progression of 0.3 (0.4) mm by SVS in the control group throughout a 12-month period. We calculated 50% reduction in AL progression (reducing axial elongation by 0.15 mm) by Orth-K for the treatment group, compared with that from the control group. The sample size required was 123 participants per group, or a total sample size of 246 participants for an α level of 0.05 (2-tailed), a power of 90%. Adjusting for 20% loss to follow-up, a total sample size of the participants was equal to 308.