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Adam R. Glassman, Diabetic Retinopathy Clinical Research Network; Evaluation Of Masking Success Of Sham Ocular Injections. Invest. Ophthalmol. Vis. Sci. 2011;52(14):1689.
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To evaluate the success of masking study participants to treatment allocation using sham intravitreal injections in a DRCR.net multicenter randomized clinical trial.
Participants with one study eye were randomized to: (1) prompt laser plus sham injection as often as every 4 weeks, (2) prompt laser plus intravitreal ranibizumab as often as every 4 weeks, (3) deferred laser plus intravitreal ranibizumab as often as every 4 weeks or (4) prompt laser plus intravitreal triamcinolone injections as often as every 16 weeks with sham injections as often as every 4 weeks. Participants with 2 study eyes were randomly assigned to sham+prompt laser in one eye and one of the other 3 treatments in the other eye. Sham injections were used to mask injections, while there was no masking of laser treatment. Sham and intravitreal injections were performed using the same procedures. For sham injections, the hub of a syringe (no needle) was pressed against the conjunctiva to simulate the force of a real injection. At the 1 year visit, each participant was asked if they thought the injections received during the study were real, sham, or sometimes real and sometimes sham.
Among the 423 participants with one study eye, the correct assignment was stated by 10% of the sham+prompt laser group (90% thought they had received real intravitreal injections), 88% of the ranibizumab+prompt laser group, 90% of the unmasked ranibizumab+deferred laser group, and 44% of the triamcinolone+prompt laser group. Among the 112 participants with 2 study eyes, the correct assignment was stated for the eye receiving real injections for 84% of the ranibizumab+prompt laser eyes, 88% of the ranibizumab+deferred laser eyes, and 31% of the triamcinolone+prompt laser eyes. Among these participants the correct assignment was stated for 24% of the sham+prompt laser eyes.
Successful masking of an intravitreal injection can be accomplished when a detailed injection procedure is followed which carefully mimics a true injection procedure. Masking appears less successful when one eye is receiving a real injection and the other eye is receiving a sham injection or an individual eye sometimes receives a real and sometimes a sham injection.
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