IMPORTANCE While medication efficacy is well documented in clinical trials, less is known of medication effectiveness in real-world clinical settings. OBJECTIVE To assess the effectiveness of intraocular pressure (IOP)-lowering medications in patients with open-angle glaucoma. DESIGN, SETTING, AND PARTICIPANTS Prospective, multicenter, interventional cohort from the prerandomization phase of a randomized clinical trial at multiple ophthalmology clinics. A total of 603 patients (603 eyes) with primary open-angle glaucoma who were using up to 3 glaucoma medications were included. INTERVENTIONS One IOP measurement was made while the patient was using his or her usual medications to lower IOP (ON IOP). Eligible participants underwent washout of all IOP-lowering drops, and the diurnal IOP was measured 2 to 4 weeks later (OFF IOP). MAIN OUTCOMES AND MEASURES Difference between OFF IOP and ON IOP. The hypothesis was formulated after data collection. RESULTS The mean (SD) ON IOPs for participants using 0 (n = 102), 1 (n = 272), 2 (n = 147), or 3 (n = 82) medications were 24.2 (3.2), 17.5 (3.2), 17.2 (3.1), and 17.2 (3.1)mmHg, respectively. Patients not using medication had a mean (SD) IOP decrease of 0.2 (2.8)mmHg at the OFF visit. Patients using 1, 2, and 3 medications had mean (SD) IOP increases of 5.4 (3.0), 6.9 (3.3), and 9.0 (3.8)mmHg, respectively, at the OFF visit. The percentages of patients with less than a 25%increase in IOP were 38%, 21%, and 13%for those using 1, 2, and 3 medications, respectively. CONCLUSIONS AND RELEVANCE Discontinuation of 1, 2, and 3 medications was associated with a clinically significant increase in IOP, although with smaller effects for the second and third medications compared with the first medication. A substantial proportion of patients showed only small changes in IOP after medication washout, suggesting either that they were not using the medication effectively or that the medication itself, although used properly, was not lowering the IOP.
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