Selective laser trabeculoplasty (SLT) has been shown to be a safe, well tolerated, and effective intraocular pressure reduction therapy for several forms of open-angle glaucoma. SLT produces significantly less disturbance to the trabecular meshwork and is theoretically more repeatable than the ALT procedure. This retrospective research will begin with cases treated in 2001. It will evaluate whether SLT is effective for patients who have had prior treatment with ALT and it will determine whether the IOP lowering effect is sustainable over time. It will also assess the efficacy of repeated SLT procedures.