The Asia Primary Tube Versus Trab (TVT) Study

Inclusion Criteria: 1. Open angle glaucoma including primary open angle glaucoma, pseudoexfoliative or pigmentary glaucoma. 2. IOP \> 18 mm Hg on 2 or more medications on at least 2 visits 3. Informed consent given and consent form signed. Exclusion Criteria: 1. Unwilling or unable to give consent, unwilling to accept randomisation, or unable to return for scheduled protocol visits. 2. Pregnant or nursing women 3. No light perception vision 4. Previous incisional intraocular surgery, other than uncomplicated clear corneal cataract surgery 5. Previous ocular laser in study eye (keratorefractive surgery and cyclodestructive procedure), except for laser trabeculoplasty procedures (Argon Laser and Selective Laser Trabeculoplasty) 6. Iris neovascularisation or proliferative retinopathy 7. Primary angle closure or primary angle closure glaucoma 8. Iridocorneal endothelial syndrome or anterior segment dysgenesis 9. Epithelial or fibrous downgrowth 10. Aphakia 11. Chronic or recurrent uveitis 12. Severe posterior blepharitis 13. Unwilling to discontinue contact lens use after surgery 14. Glaucoma secondary to penetrating keratoplasty, trauma, steroids, retinal disease/surgery or neovascular disease 15. Conjunctival scarring from prior ocular surgery, trauma or cicatrizing disease precluding a superior trabeculectomy 16. Need for glaucoma surgery combined with other ocular procedures (i.e. cataract surgery, penetrating keratoplasty, or retinal surgery) or anticipated need for urgent additional ocular surgery 17. Advanced glaucoma with MD \<-20dB