The Collaborative Initial Glaucoma Treatment Study (CIGTS), a randomized, controlled clinical trial, is being conducted to determine whether patients with newly diagnosed OAG are best managed by the conventional approach of topical pharmacologic agents or by immediate filtration surgery. Eligible patients were randomized to receive either a stepped medication treatment regimen or filtration surgery to control their OAG. Sample size requirements indicated that 300 patients were needed for each treatment approach; a total of 607 patients were ultimately recruited for the CIGTS.