Visual acuity outcomes among sham vs no-treatment controls from randomized trials

To compare 2-year visual acuity outcomes between similar participants assigned to sham and no-treatment control arms in randomized clinical trials.

We retrospectively matched sham controls from 2 randomized trials to no-treatment controls (no sham or placebo) from 3 trials on 8 baseline prognostic criteria (full matches) or on 4 to 7 criteria (partial matches). Outcomes were compared using data from those who had 2-year visual acuity measurements and also using the last observation carried forward method to impute missing 2-year measurements.

A full match to a no-treatment control was identified for 72 of 321 sham controls (22%); a partial match was identified for another 93 sham controls (29%). Among the fully matched pairs, no important difference in 2-year visual acuity outcomes was observed. However, 2-year outcomes differed somewhat between sham and no-treatment controls within the partially matched pairs.

Findings from fully matched pairs suggest that sham treatment to mask participants in clinical trials may be unnecessary when visual acuity is the outcome of interest. However, findings from the partially matched pairs do not fully support this conclusion. This analysis challenges the necessity for sham (placebo) controls in randomized clinical trials in ophthalmology when visual acuity is the primary outcome of interest.