Obstruction of the Tube/Valve

Tube shunt obstruction is a relatively common complication, with reported rates up to 15%. Tube obstructions can be divided into 2 basic types: 1) distal tube obstruction in the anterior chamber, ciliary sulcus, or pars plana; and 2) proximal tube obstruction at the tubeplate junction. Occasionally tube obstruction may lead the surgeon and patient to believe that the tube shunt was never successful at controlling intraocular pressure (IOP) postoperatively. This complication generally has a high impact on the patient’s postoperative course. Preoperative planning and careful surgical technique can avoid many cases of obstruction. Distal tube obstruction is typically a serious postoperative complication, with a sudden elevation in IOP resulting in pain, inflammation, and worsened vision. The distal end of the tube may be obstructed by blood, fibrin, iris, vitreous, lens material, silicone oil, and/ or viscoelastic. Treatment is tailored to the immediate cause. No matter what the cause of obstruction, if tube repositioning becomes necessary, the use of tube extenders, available either commercially or created with readily available 22-gauge angiocatheter sleeves and silicone tubing (used for nasolacrimal duct intubation), facilitate this procedure if the tube is too short to reposition (see Chapter 30). If a blood clot or fibrin is present, observation with use of ocular hypotensive agents and frequent (every 1–2 hours) application of topical prednisolone acetate, 1% may be sufficient. Tissue plasminogen activator (tPA) also may be injected into the anterior chamber to rapidly resolve the clot. The usual dose of tPA is 12.5 μg in 0.1 cc (0.1 mL) and is readily available from most hospital pharmacies. Multiple injections may be required, but concerns about cost have lessened with the advent of a recombinant form of tPA. In one series of 36 patients treated with tPA after tube shunt surgery, severe hyphema, flat anterior chamber, and profound hypotony were seen after 11% (6 of 55) tPA injections. Blood in the tube may be flushed out with balanced saline solution, using a 27-gauge cannula inserted into the eye through a paracentesis wound. If the tube is buried in the iris, pilocarpine may pull the iris out of the tube.