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This study evaluated the effect of preoperative brimonidine tartrate 0.2% on intraocular pressure (IOP) during robotic-assisted laparoscopic radical prostatectomy in steep Trendelenburg position (sTBURG).In this prospective randomized controlled masked interventional trial, eligible patients scheduled for robotic-assisted laparoscopic radical prostatectomy in sTBURG at the Toronto General Hospital had one eye randomized to placebo (artificial tears) or drug (brimonidine tartrate 0.2%) preoperatively. Visual acuity (VA), tonometry, disc photography, visual field (VF), and retinal nerve fiber layer (RNFL) assessments were performed preoperatively and postoperatively. A standardized anesthetic protocol was followed intraoperatively. IOP was measured using Tono-Pen AVIA (Reichert Inc., New York, NY) as follows: preanesthesia supine, anesthetized supine, hourly in sTBURG and awake supine. The primary outcome was IOP in sTBURG in the drug group compared with the placebo group. Secondary outcomes were changes in VA, VF, RNFL thickness, mean arterial pressure, and ocular perfusion pressure. This study was approved by University Health Network Research Ethics Board.In total, 26 eligible patients, mean age 61.9±5.1 years, were randomized to brimonidine (11 patients) and placebo (15 patients). Baseline IOP was not significantly different between the drug and placebo groups (P=0.42). Significant and sustained IOP elevation of >1.5X baseline in the sTBURG was noted in both groups. The mean IOP 1 hour after sTBURG was 29.4±6.9 and 27.2±3.4 mm Hg in the drug and placebo groups, respectively (P=0.35). No significant changes were noted in VA, VF, or RNFL.Significant and sustained IOP increases occur during sTBURG. Preoperative brimonidine does not prevent IOP spikes in sTBURG.