Glaucoma Drainage Implant

A glaucoma drainage implant (GDI) is a silicone tube connected to a polypropylene or silicone end-plate placed under the conjunctiva and Tenon's capsule, typically in the superotemporal quadrant. Aqueous flows from the anterior chamber through the tube to a fibrous capsule that forms around the plate, where it is reabsorbed. Valved devices (Ahmed FP-7) limit flow above ~8 mmHg; non-valved devices (Baerveldt 350, Molteno) require ligation or staged opening to prevent early hypotony.

GDIs are indicated when trabeculectomy has failed or is unlikely to succeed, including neovascular glaucoma, uveitic glaucoma, ICE syndrome, aphakic and pseudophakic glaucoma, post-penetrating keratoplasty glaucoma, and pediatric refractory glaucoma. Five-year IOP control rates are 60-80% with a mean reduction of 30-50% from baseline; valved and non-valved devices show similar long-term outcomes with different complication profiles.

Surgery places the plate 8-10 mm posterior to the limbus, secures it to the sclera, and inserts the tube into the anterior chamber, ciliary sulcus, or pars plana with patch graft (donor sclera, pericardium, cornea) coverage. Postoperative complications include early hypotony, choroidal effusion, tube migration or exposure, corneal endothelial decompensation, motility disturbance, encapsulated bleb with pressure spikes, and endophthalmitis. Long-term IOP often plateaus around 14-18 mmHg with adjunctive medications.