This is a multi-center, outpatient study assessing equivalence of the Titanium Sapphire laser (TiSaLT) to the Argon laser (ALT) in the ability to reduce IOP in patients having primary open angle glaucoma in eyes with poorly controlled IOP on maximally tolerated medications and/or prior failed glaucoma surgery. Approximately 120 patients are to be enrolled in the study, with approximately equal numbers of patients enrolled at each of the investigational sites. The investigational sites are to accrue patients with poorly controlled open-angle glaucoma on maximal tolerated medical therapy and/or patients with previously failed laser trabeculoplasty. One half of the eyes will be randomized to treatment with the Argon laser (ALT) as the concurrent control group and the other half will be treated with Titanium Sapphire (TiSaLT) laser.