What is the role of glaucoma drainage devices in the treatment of penetrating keratoplasty and glaucoma (PKPG)?

Updated: Dec 30, 2020
  • Author: Shibandri Das, MD; Chief Editor: Inci Irak Dersu, MD, MPH  more...
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Glaucoma drainage devices create an alternate aqueous pathway by channeling aqueous from the anterior chamber through a long tube to an equatorial plate that promotes bleb formation. Kirkness [65]  first reported the use of GDDs in PKPG. Even though GDDs appear to control glaucoma in a high percentage of patients in several published series (71-96% at 1 year, 44-87% at 2 years, and 71-83% at 5 years), it appears to be associated with a high incidence of graft failure in the range of 10 to 51% (with an average of 36.2%). [22, 41, 65, 66, 67, 68]  The etiology of graft failure is probably multifactorial. The presence of underlying chronic inflammation and extensive peripheral synechiae and a history of multiple previous surgeries may compromise the graft. The introduction of a GDD into the anterior chamber may also be associated with increased inflammation and corneal endothelial damage and may further compromise the graft.

Ritterband and the Cornea Glaucoma Implant Study (COGIS) Group [69]  reported on 83 eyes treated with a combination of PKP and implantation of a GDD, with tube placement in the pars plana. Their graft survival rates are among the best reported for this combination of surgeries, with clear grafts in 93% of the treated eyes at 6 months, 87% at 1 year, and 59% at 2 years; however, no grafts remained clear in the small group of patients at 5-year follow-up.

The timing of GDD surgery is another factor that can contribute to graft failure. In the series published by Rapuano and colleagues [66]  and Beebe and colleagues, [67]  a trend toward a higher incidence of graft failure when GDD surgery was performed after PKP was observed. Other studies report no association between timing of GDD implantation relative to PKP and graft survival or IOP control. [70]

With all this inconsistency, the choice of the GDD in the treatment of patients with PKPG depends on the condition of the eye and the surgeon. Four main GDDs are available: the Ahmed, Krupin, Molteno, and Baerveldt implants. The Ahmed implant and the Krupin implant offer resistance to the outflow in the form of a sheet valve and a slit valve, respectively. [41]  The Molteno implant and the Baerveldt implant provide no resistance to the outflow and, thus, may lead to hypotony. [71]  This problem can be overcome with the use of the ripcord technique and/or ligation with a dissolvable suture.

The advantages of the valved implants, especially those of the Ahmed glaucoma valve, appear to be easy insertion after single-quadrant dissection and a low incidence of hypotony in the immediate postoperative phase; however, the Ahmed valve is associated with a high incidence of the hypertensive phase, which may require needling with 5-FU injections. [41]  In a case series of 59 high-risk PKP eyes that underwent Ahmed glaucoma device insertion, Almousa and colleagues [72]  report IOP control success rates of 96% of the eyes at 1 year and 83% at 5 years, but clear corneal graft percentages of 87% at 1 year and 47% at 5 years. 

On the other hand, GDDs with a larger surface area, such as the double-plate Molteno and Baerveldt implants, appear to exhibit a lesser incidence of the hypertensive phase and may achieve slightly lower IOP.71 The overall success rate and the frequency of complications, including corneal decompensation, appear to be similar for all GDD. [41, 66, 68]  Complications of GDD surgery include increased rate of graft rejection and failure (compared with trabeculectomy), conjunctival erosion, prolonged hypotony, tube-endothelial touch, tube obstruction, tube failure, retinal detachment, tube plate extrusion, epithelial downgrowth, and infection.

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