Tube Shunt Related Complications of the Anterior Chamber

Abstract

Postoperative complications in the anterior chamber can affect both glaucoma progression and vision. Preoperative considerations and surgical technique are important to reduce and prevent these complications. A flat anterior chamber is one of the most common complications following tube shunt surgery, occurring at a rate of 3.5%– 27%. Although often associated with hypotony and choroidal effusions and usually due to increased outflow after surgery, it may also be related to decreased aqueous production, especially in eyes with previous ciliary body ablation. Increased outflow could result from leakage around the tube or overfiltration either before fibrous capsule formation over the plate or through tube fenestrations. Diagnosis of the cause of hypotony can be made with a careful slit-lamp examination. Leakage around the tube can be viewed internally by gonioscopy, though a flat or shallow anterior chamber can make seeing potential leakage difficult. The location of overfiltration can be determined by looking at areas of conjunctival elevation. Conjunctival bleb formation at the limbus could help identify leakage around the tube at its scleral tunnel insertion. Early elevation of a bleb over the reservoir of a tube shunt is also seen with incomplete occlusion in the nonvalved (or sometimes valved) tube. Elevation near the tube-plate junction could also indicate overflow at a fenestration but is unusual. Intracameral irrigation of fluorescein can help identify the source of leakage. A flat anterior chamber associated with hypotony can have serious sequelae, including corneal edema, cataract, and failure of the procedure. Medical treatment to deepen the anterior chamber with cycloplegics and reduction of wound healing inhibitors should be tried first but is often insufficient, as this treatment will not quickly eliminate the source of leakage. More aggressive intervention will be needed if there is central flattening (Grade 2 or 3 flat chamber). Identifying the source of leakage is important in determining management. If there is leakage at the site of the tube’s entry into the sclera, viscoelastic may be needed to fill the anterior chamber. Air injection is an alternative that allows for continued visualization of the leak if desired.