Plate-based tube implants tend to require fewer interventions in the postoperative period compared with trabeculectomy. However, complications can occur (Table 13-5).
Elevated IOP in the early postoperative period can have various causes. The hypertensive phase is marked by a sudden elevation of IOP after previously well-functioning surgery. Usually occurring between 3 weeks and 3 months after surgery, it is caused by decreased permeability of the capsule that forms around the end plate. Over time, the hypertensive phase may resolve as the capsule reorganizes and becomes more permeable to aqueous. Thus, management involves medical treatment to keep the pressure reasonably low while the capsule reorganizes. The incidence of this complication is higher with the Ahmed implant than with the Baerveldt implant, perhaps because the capsule is exposed to aqueous in the early postoperative period with the Ahmed device. Conversely, with Baerveldt implants, exposure of the capsule to aqueous is delayed by the ligature. The use of aqueous suppression early in postoperative management (when the IOP reaches approximately 10–12 mm Hg) is associated with a reduction in the incidence of the hypertensive phase and improved long-term outcomes. Evidence is mixed regarding the value of intraoperative or postoperative adjunctive MMC or 5-FU with tube shunt surgery; however, clinical trials are in progress.
Other causes of elevated IOP in the postoperative period include a defective valve mechanism and occlusion. Tubes can become occluded with fibrin, blood, vitreous, or iris tissue. A peripheral iridotomy can remedy iris occlusion, while fibrin and heme will usually clear over time without intervention. Elevated IOP in Baerveldt shunts that have been ligated can be managed by applying a green or diode laser to the ligature with settings similar to those used for nylon suture lysis. If a rip cord has been placed, it can be pulled. However, if these procedures are performed too early, hypotony may ensue. Fenestrations can also be created at the slit lamp to provide temporary IOP relief while waiting for the ligature to dissolve.
Shallow anterior chamber in the postoperative period occurs for reasons similar to those seen after trabeculectomy. Choroidal effusions and malignant glaucoma are managed in a similar fashion. Overfiltration may require a return to the operating room to either ligate the tube or place a suture in the lumen of the tube to restrict aqueous outflow.
Tube erosion occurs in 1%–8% of plate-based tube implant surgeries (Fig 18-13). The causes include mechanical factors, immune response, and fragile conjunctiva overlying the tube. Tube erosion requires surgical correction, as patients with this complication are at high risk for infection. Repair may involve placing a new allograft, moving the tube to a different location, or removing the tube (Video 13-12). The risk of endophthalmitis after tube shunt surgery is about 0.5% in 5 years. Management of endophthalmitis often requires tube removal.
Table 13-5 Complications of Tube Shunt Surgery and Options for Their Prevention and Management
Courtesy of Chandrasekharan Krishnan, MD.
Figure 13-18 Tube exposures increase the risk of developing endophthalmitis and should be repaired urgently.
(Courtesy of Chandrasekharan Krishnan, MD.)
Diplopia occurs in about 5% of patients. It is often due to displacement of the globe by a large bleb or injury or impingement of an extraocular muscle. Management with prisms is usually successful. If the deviation precludes prism use, strabismus surgery or tube removal may be indicated.
Bains U, Hoguet A. Aqueous drainage device erosion: a review of rates, risks, prevention, and repair. Semin Ophthalmol. 2018;33(1):1–10.
Cui QN, Hsia YC, Lin SC, et al. Effect of mitomycin C and 5-fluorouracil adjuvant therapy on the outcomes of Ahmed Glaucoma Valve implantation. Clin Exp Ophthalmol. 2017;45(2):128–134.
Pakravan M, Rad SS, Yazdani S, Ghahari E, Yaseri M. Effect of early treatment with aqueous suppressants on Ahmed Glaucoma Valve implantation outcomes. Ophthalmology. 2014;121(9):1693–1698.
Yazdini S, Doozandeh A, Pakravan M, Ownagh V, Yaseri M. Adjunctive triamcinolone acetonide for Ahmed Glaucoma Valve implantation: a randomized clinical trial. Eur J Ophthalmol. 2017;27(4):411–416.
Zheng CX, Moster MR, Khan MA, et al. Infectious endophthalmitis after glaucoma drainage implant surgery: clinical features, microbial spectrum, and outcomes. Retina. 2017;37(6):1160–1167.
Excerpted from BCSC 2020-2021 series: Section 10 - Glaucoma. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.