Sample size
degenerative disease, choroideremia, ≥15-letter BCVA gain
CHOROIDEREMIA
Sample size estimation was performed using Fisher’s exact test. Considering that choroideremia is a degenerative disease, it was assumed that a ≥15-letter BCVA gain would not be observed in participants without treatment. Assuming that 16.7% of the treated participants would gain ≥15 letters in BCVA at 12 months, 56 participants in the high-dose group and the control group would provide ≥90% power at a 0.05 level of significance with a two-sided test. To be conservative, 64 participants in the high-dose group and 64 participants in the control group were needed to ensure 85% power in case one participant in the untreated control group had ≥15-letter BCVA gain by chance, which corresponded to a total of 160 participants completing the study (64 participants in the high-dose group, 32 in the low-dose group and 64 in the control group).