Analysis
The trial sample size was calculated on the main outcome of the study. With a sample size in each sequence group of 100 (a total sample size of 200), a 2 × 2 crossover design would have 80% power to detect a difference in mean intra-patients global score of 3.0 assuming that the crossover ANOVA √MSE is 10.607 (the standard deviation of differences, σd, is 15.0) with a 0.05 two-sided significance level. The total sample size was adjusted to 220 patients considering an expected dropout rate of about 10%.The primary outcome analysis was performed on the composite score of the Visual Function Questionnaire-25 (VFQ-25) [