Patients are followed for a minimum of 4 years to assess the development of glaucoma progression. They are seen every 3 months to collect visual field, IOP, and other data. Disc photographs are taken every 6 months. Technicians and disc photograph graders are masked regarding treatment assignment. Additional followup visits are held to confirm visual field progression and IOP elevation (>25 mm Hg in treated group, >35 mm Hg in control group). Patients in the treated group receive Xalantan whenever IOP exceeds 25 mm Hg at more than one visit; patients in the control group will receive Xalantan whenever IOP reaches 35 mm Hg or higher during the trial. If IOP remains high, individualized treatment is given. All patients continue to be followed to monitor the development of end points and will be analyzed in their originally assigned groups.