The Early Manifest Glaucoma Trial (EMGT) is the first large, controlled, randomized clinical trial to evaluate the effect of lowering the intraocular pressure on the progression of newly detected, open-angle glaucoma. This study will compare glaucoma progression in initially treated versus untreated patients with newly detected open-angle glaucoma and will allow quantification of the effect of immediate IOP-lowering treatment on progression during the followup period.