Feasibility of using placebo vision therapy in a multicenter clinical trial

The Convergence Insufficiency Treatment Trial (CITT) Investigator Group conducted a preliminary study assessing the effectiveness of home-based push-up therapy and office-based vision therapy/orthoptics for the treatment of convergence insufficiency (CI). The CITT group developed a placebo therapy program that was designed to simulate real vision therapy/orthoptics. The purpose of this paper is to evaluate the effectiveness of this placebo therapy program in maintaining masking of subjects randomized to the office-based treatment arms (real or placebo).

Subjects (ages 9 to 30 years) were enrolled, stratified into two groups by age, and then randomly assigned to one of three treatment groups: pencil push-up therapy, office-based vision therapy/orthoptics, or office-based placebo vision therapy/orthoptics. At the end of treatment, subjects in the two office-based therapy groups (placebo and real) were asked: (1) which treatment do you think you received? and (2) how sure are you about your answer?

Ninety-five percent of subjects assigned to real therapy and 83% assigned to placebo therapy thought they were in the real therapy group. Of the subjects who thought they received real therapy, 90% assigned to real therapy and 89% assigned to placebo therapy were "somewhat sure," "pretty sure," or "very sure" of their answer. Those assigned to real therapy had more responses in the "very sure" category.

The CITT placebo therapy program was effective in maintaining subject masking in this multicenter clinical trial.