Based on our preliminary results (n=6 per group) showing the significant mean difference of postoperative visual acuity between C-SMILE and L-SMILE, a priori power analysis was performed. Group sample sizes of 54 and 81 achieved 81% power to detect a difference of - 0.1 between the null hypothesis that both group means are 0.0 and the alternative hypothesis that the mean of group 2 is 0.1 with estimated group standard deviations of 0.1 and 0.1 and with a significance level (alpha) of 0.05 using a two-sided two-sample t-test. Therefore, we confirmed that sample size of L-SMILE is 60 and one of C-SMILE is 90 as considering 10 % reduction.