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This prospective randomized parallel group clinical trial by Camras and Sheu (266) investigated the comparative efficacy and tolerability of latanoprost at 8PM (n = 152) and brimonidine 8:AM and 8:PM (n = 151) for lowering IOP in a mixed population including both naïve and previously treated patients with POAG or ocular hypertension. Evaluators were masked to agents and the main outcome measure was the difference in diurnal IOP change between start and six months. IOPs were taken at 8:00AM, 10AM, 12 noon, and 4PM at baseline and at months three and six visits. Preplanning included calculating a sample size (n = 300) sufficient to detect a 1.5 mm difference in mean diurnal IOP reduction between groups, with an = 0.05 (two-sided) and a power of 80%. Analyses were done using an intention-to-treat strategy. Latanoprost was administered at 8.00 AM rather than at bedtime. Diurnal variations were less among patients in the latanoprost group than among those in the brimonidine group and five times more patients withdrew from the brimonidine group (23/152) due to adverse side effects than from the latanoprost group (4/151). The results of this well-planned and executed randomized trial are consistent with a prior European study1 and with general clinical experience as to the superiority of latanoprost's efficacy and tolerability compared to brimonidine for IOP control. Although only three time-points were measured daily three months and at six-months, the choices of IOP measurement times were appropriate for the comparative study. AM dosing of latanoprost may have minimized the mean IOP diurnal difference between drugs calculated at six months as 2.5mmHg in favor of latanoprost.