Subjects will undergo washout of pre-study IOP-lowering medications for the appropriate duration, then undergo 2 eligibility visits. Eligible subjects will be randomized 1:1, to receive masked SIMBRINZA ® or Vehicle for 4 weeks. Two 24-hour visits will be conducted (Day 0 and Week 4) during which intraocular pressure will be collected every 2 hours. The expected duration of subject participation in the study is 10 weeks.