The Ahmed vs. Baerveldt (AVB) Study is the first multicenter prospective randomized clinical trial comparing the Ahmed FP7 valve and the Baerveldt-350 tube shunt glaucoma drainage devices. Primary outcome is surgical failure, a composite criteria evaluating the intraocular pressure lowering effect of the devices, complications of the surgery, treatments for complications, glaucoma medication use, and the preservation of visual acuity. Secondary outcomes will evaluate these variables individually, and any non-glaucoma related ocular pathology and required interventions.