 This triple-blind, stratified, randomized clinical trial includes 100 eyes of 100 patients aged 18 to 85 years with refractory glaucoma. Eligible subjects undergo stratified block randomization; eyes are first stratified to one of four subgroups: group 1:patients with previous failed trabeculectomy, group 2: uveitic glaucoma, group 3: neovascular glaucoma and group 4: other indications like aphakic glaucoma or glaucoma associated with vitreoretinal procedures. 