Glaucoma Drainage Devices

Glaucoma Drainage Devices

Laura A. Vickers

Nathaniel C. Sears

JoAnn A. Giaconi

Marlene R. Moster


• Glaucoma drainage devices (GDDs) are designed to lower intraocular pressure (IOP). They are also known as aqueous shunts, aqueous shunting devices, or tube shunts.

• Traditionally, they have been used to lower IOP in cases of failed filtration surgery and recalcitrant and complex glaucomas, such as inflammatory, neovascular, and traumatic glaucoma. Increasingly, since the publication of the Tube versus Trabeculectomy Study that compared Baerveldt 350-mm2 implants to trabeculectomy with mitomycin-C,1 some centers are using GDDs as a primary glaucoma surgery.

• All GDDs consist of a silicone tube connected to an episcleral plate (or explant), which is made of various materials in different shapes and surface area sizes depending on the specific model (Figs. 25-1 and 25-2). The plate is placed against the sclera at the globe’s equator, while the tube is inserted into the anterior chamber (or, more rarely, through the pars plana). Despite nonreactive materials, a collagenous and fibrovascular capsule (or bleb) develops around the episcleral plate. Once within the bleb, aqueous flows passively through the wall of the capsule and is reabsorbed by venous capillaries and lymphatics.

• GDDs can be divided into restrictive and nonrestrictive devices.

  • Nonrestrictive, or nonvalved, devices permit the free flow of fluid from inside the eye to the episcleral plate. Nonrestrictive shunts in today’s market include the various models of the Molteno and Baerveldt GDDs (Fig. 25-1). Resistance to outflow depends on the density of the capsule that forms around the plate.

  • Restrictive, or valved, devices incorporate a flow-controlling element within the posterior part of the tube (i.e., valve or membrane) designed to limit fluid flow in an attempt to prevent postoperative hypotony. Restrictive models available are the Ahmed (Fig. 25-2) and Krupin GDDs.

• Thus far, no one GDD model is superior to the others. The Ahmed Baerveldt Comparison Trial was a multicenter, randomized clinical trial comparing the safety and efficacy of the Ahmed FP-7 and Baerveldt 350-mm2 implants. At 5-year follow-up, mean IOP was lower in the Baerveldt group on a similar number of
glaucoma medications, but that there were also a greater number of early and serious complications in the Baerveldt group compared to the Ahmed group.2 The Ahmed versus Baerveldt study also compared these two devices. After 5-year follow-up, the Baerveldt group had a significantly lower cumulative probability of failure and required fewer medications than the Ahmed group, but it also experienced more hypotony-related complications.3

FIGURE 25-1. Nonrestrictive glaucoma drainage devices. Models commercially available. A-D. Molteno devices. The newer Molteno3 shunts (A and B) are characterized by a larger, more flexible episcleral plate than the older models (C and D). Numbers adjacent to the models indicate surface area of the episcleral plate. E and F. Baerveldt devices, the plates of which are made of barium-impregnated silicone.


1. Gedde SJ, Schiffman JC, Feuer WJ, Herndon LW, Brandt JD, Budenz DL; Tube versus Trabeculectomy Study Group. Treatment outcomes in the Tube versus Trabeculectomy study after five years of follow-up. Am J Ophthalmol. 2012;153(5):789-803.

2. Budenz DL, Barton K, Gedde SJ, et al. Five-year treatment outcomes in the Ahmed Baerveldt Comparison Study. Ophthalmology. 2015;122(2):308-316.

3. Christakis PG, Kalenak JW, Tsai JC, et al. The Ahmed versus Baerveldt Study: five-year treatment outcomes. Ophthalmology. 2016;123(10):2093-2102.

FIGURE 25-2. Restrictive devices. Ahmed valves come with a flexible plate (FP models) or a rigid polypropylene plate (S models). The smaller sizes are intended for pediatric eyes. The double-plate model consists of a valved plate connected to a nonvalved plate by an intervening silicone tube that crosses over a rectus muscle (in this figure, the intervening tube is not connecting the two plates on the bottom right).


• Local anesthesia is recommended because some of the surgical steps can be painful without adequate anesthesia. A retrobulbar, peribulbar, or sub-Tenon’s injection can be utilized.

• The superotemporal quadrant (Fig. 25-3) is the preferred location for implantation of the first GDD (additional shunts can be implanted in other quadrants). For better exposure of the surgical site, a corneal traction (Fig. 25-4) or superior rectus bridle suture is helpful. The tube should be flushed with balanced salt solution to ensure patency using a 30-gauge cannula.

• Generally, a fornix-based peritomy is used. A 90- to 110-degree conjunctival incision is adequate for single-plate implants. Stevens tenotomy scissors are used to bluntly dissect posteriorly in the quadrant to make room for the plate. The episcleral plate is placed between adjacent rectus muscles with its anterior edge at least 8 mm posterior to the limbus (Fig. 25-5). Nonabsorbable sutures (6-0 to 8-0 nylon, prolene, mersilene) are passed through the fixation holes of the episcleral plate and sutured to the sclera.

• The optimal length of tubing is estimated by laying the tube across the cornea. The tube is then trimmed, bevel up, to extend 2 to 3 mm into the anterior chamber (Fig. 25-6). A corneal paracentesis is made to provide access to the anterior chamber in case of collapse (Fig. 25-7). A 22- or 23-gauge needle is used to create a track into the anterior chamber, parallel to the plane of the iris, starting approximately 1 to 2 mm posterior to the corneoscleral limbus (Fig. 25-8). The tube is then inserted through this track into the anterior chamber with smooth forceps (Fig. 25-9).

• Proper positioning of the tube in the anterior chamber is essential, ensuring that it does not touch the iris, lens, or cornea. The tube may or may not be fixed to the sclera with sutures of 10-0 nylon or prolene (Fig. 25-10). This anterior suture is wrapped tightly around the tube to prevent movement into or out of the anterior chamber, but not so tightly that it occludes the tube lumen. To avoid conjunctival erosion by the tube, processed pericardium, donor sclera or cornea, and, less commonly, fascia lata or dura, are used to cover the anterior scleral portion of the tube (Figs. 25-11 and 25-12). The patch graft is sutured in place using interrupted sutures. Alternatively, a partial-thickness limbal-based scleral flap can be fashioned, and the tube entry is made underneath this flap, so that the sutured flap covers the tube (Figs. 25-13 and 25-14).

• The tube can also be placed through the pars plana (Figs. 25-8, 25-9, 25-10, 25-11, 25-12, 25-13, 25-14, 25-15, 25-16, 25-17, 25-18, 25-19, 25-20, 25-21, 25-22, 25-23, 25-24, 25-25, 25-26, 25-27, 25-28, 25-29, 25-30 and 25-31) in cases where placement into the anterior chamber is difficult or undesirable. This approach requires a pars plana vitrectomy by a retina surgeon with careful attention to remove the vitreous skirt in the quadrant where the tube will be inserted.

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May 4, 2019 | Posted by in OPHTHALMOLOGY | Comments Off on Glaucoma Drainage Devices

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