Hypotony after fistulizing surgery is common, and most cases resolve without complications. Occasionally, a flat anterior chamber in phakic or pseudophakic eyes may lead to corneal decompensation or cataract formation. In aphakic eyes that have undergone previous vitreous surgery, flat anterior chambers will not develop, but large choroidal detachments and delayed suprachoroidal hemorrhage may occur while the eye is soft. To maintain intraocular pressure (IOP) in the early postoperative period, the authors used a technique to seal the drainage tube with a Vicryl tie, combined with injection of sodium hyaluronate, sulfur hexafluoride (SF6), or perfluoropropane (C3F8), perioperatively in 28 eyes undergoing glaucoma tube implant surgery. Eight eyes were treated with injection of sodium hyaluronate, 8 with SF6, and 12 eyes with C3F8. Hypotony was significantly less frequent in eyes treated with C3F8 compared with sodium hyaluronate (P less than 0.05). Mean IOP was significantly higher for eyes treated with C3F8 injection compared with sodium hyaluronate for the first 4 days after surgery (P less than 0.05).