Validation of a questionnaire for comparing the tolerability of ophthalmic medications

Purpose: The Comparison of Ophthalmic Medications for Tolerability (COMTOL) questionnaire was developed for use in clinical trials to compare the tolerability of topical ophthalmic medications used in the treatment of glaucoma. The questionnaire captures the frequency and bother of common side effects (i.e., ocular and other local effects, and effects on visual function) of topical therapy for lowering intraocular pressure. In addition, the questionnaire measures the extent to which these side effects and any associated limitations in routine living activities interfere with health-related quality of life, medication compliance, and patient satisfaction with the medication, This study was designed to assess the measurement characteristics of the COMTOL questionnaire, Methods: The internal consistency, reliability, reproducibility, construct validity, discriminant validity, and responsiveness of the questionnaire were assessed in 70 adult patients with glaucoma in a clinical trial comparing timolol and pilocarpine, Results: The questionnaire showed good-to-excellent internal consistency (0.73 to 0.98), reliability (0.76 to 0.94), and reproducibility (0.75 to 0.93). In general, there was a strong correlation in the expected direction between the frequency and bother of side effects and patient-perceived global measures. The questionnaire discriminated between patients receiving timolol and patients receiving pilocarpine. The questionnaire demonstrated significant responsiveness to change, Conclusions: The COMTOL questionnaire showed acceptable measurement characteristics for inclusion as a tolerability measure to supplement spontaneous adverse event reporting in clinical trials of topical ophthalmic therapy.