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. Author manuscript; available in PMC: 2024 Oct 1.
Published in final edited form as: Int Ophthalmol Clin. 2023 Sep 27;63(4):93–101. doi: 10.1097/IIO.0000000000000499

Glaucoma Drainage Device Implantation, Outcomes, and Complications

Julius T Oatts 1, Ying Han 1,2
PMCID: PMC10807850  NIHMSID: NIHMS1922298  PMID: 37755445

Abstract

Glaucoma drainage device (GDD) surgery has gained popularity as a treatment strategy for patients with medically uncontrolled glaucoma. Glaucoma is the leading cause of irreversible blindness in the world and continues to be a major public health issue. While our understanding of glaucoma continues to evolve, the primary treatment for glaucoma continues to be intraocular pressure (IOP) control. When medical treatment fails, glaucoma surgery is considered. GDD implantation is one of the most commonly performed incisional glaucoma surgeries. GDD was originally designed for patients with secondary glaucoma and/or patients who are at an increased risk of failure after trabeculectomy. More recently, its application has been extended to primary glaucoma as the first choice of incisional surgery. This manuscript summarizes recent GDD types, implantation, clinical outcome and complications.

Introduction

Glaucoma drainage device (GDD) implantation is commonly performed for refractory glaucoma or to control glaucoma following failed trabeculectomy.1,2 In recent years, greater appreciation for GDD efficacy has prompted their expanded use in patients with many types of glaucoma, including its use as a primary surgical intervention.2–5

GDDs work by creating a subconjunctival reservoir that allows external shunting of the aqueous, which ultimately results in a reduction in the intraocular pressure (IOP). Here, we review the types of GDDs, surgical technique and device innovations as well as post-operative outcomes and complications.

Types of Glaucoma Drainage Devices and Surgical Approach

Glaucoma Drainage Device Models

Though there are many types and models of GDDs, they all share the common design which includes a tube connected to an end plate. The largest distinction is whether the device is valved or nonvalved, which refers to whether or not there is a valve mechanism present designed to limit flow through the tube and theoretically prevent hypotony.6 Valved devices provide the advantage of more immediate postoperative IOP lowering while non-valved devices provide the advantage of potentially better longer term IOP control.7 The most currently used devices include the Ahmed glaucoma valve (New World Medical, Rancho Cucamonga, California, USA), the Baerveldt glaucoma implant (Abbott Medical Optics, Abbott Park, Illinois, USA), and the Aurolab aqueous drainage implant (Aurolab, Madurai, India). Choice of GDD is often dependent upon surgeon preference, patient pathology, risk for hypotony, need for immediate IOP control, and informed by several studies comparing these devices, which are described below.

Newer Glaucoma Drainage Devices

The Paul glaucoma implant (Advanced Ophthalmic Innovations, Singapore, Republic of Singapore) is a non-valved device made of silicone with a winged end-plate and a surface area of 342.1 mm2, which is larger than that of the Ahmed glaucoma valve (184 mm2) and slightly smaller than that of the larger Baerveldt (350 mm2).8 Another innovation is a smaller internal and external tube diameter, which offers a theoretical lower risk of tube erosion or exposure. The first study to evaluate the efficacy and safety of the Paul glaucoma implant included 74 patients with minimum 1 year follow up and demonstrated good IOP control (23.1 ± 8.2 mmHg preoperatively to 13.2 ± 3.3 mmHg at 1 year) and modest complication rates (shallow anterior chamber 14.9%, hypotony requiring intervention 9.5%, tube shunt occlusion 6.8%, tube exposure 4.1%).9 Another newer glaucoma drainage device is the Ahmed Clearpath device (New World Medical, Rancho Cucamonga, California, USA). This device is non-valved and comes in two sizes (250 mm2 and 350 mm2). The major difference between this and the Baerveldt is that the Ahmed Clearpath device has a longer anteroposterior diameter and a shorter horizontal diameter. This can lead to a theoretical advantage of easier exposure to secure the plate and a more posterior bleb.8 Several small studies evaluating this device have been published and have shown an improvement in IOP (26.3 ± 9.0 mmHg preoperatively to 13.7 ± 4.7 at 6 months) and 11% requiring another surgical procedure.10

Surgical Steps of GDD Implantation

Though several surgical variations exist for GDD implantation, we will briefly review the general surgical steps as well as highlight areas of variation. First, the surgical eye is prepped and draped in standard sterile fashion. A traction suture is often placed into the superior cornea or limbus to improve exposure. A limited conjunctival peritomy is made in the quadrant of intended GDD implantation and conjunctival relaxing incisions are made. A fornix incision has also been described.11 Cautery is used as needed to achieve proper hemostasis. Scissors are used to dissect into the sub-Tenon’s space 8 mm posterior to the limbus. Both the superior rectus and lateral rectus muscles are hooked with a muscle hook. At this point, the GDD is prepared. For valved implants, the device is primed with balanced salt solution. For non-valved implants, some combination of a ripcord and/or ligating suture is placed. Ripcord sutures are typically non-absorbable, placed to occlude the os of the tube, and are left subconjunctivally at the end of the surgical procedure. Ligating sutures are tied around the tube externally to occlude flow. Fenestrating slits are often placed in non-valved devices using a needle or blade. Alternatively, placement of a wick suture is another technique that has been described to control IOP in the immediate post-operative period.12 Next, the plate of the device is placed into the sub-Tenon’s space in the desired quadrant approximately 8 mm from the limbus. The eyelets are typically secured to the sclera using non-absorbable sutures, though a sutureless approach has been described as well.13 Next, a corneal paracentesis is created through which viscoelastic is inserted into the eye to maintain the anterior chamber.

The desired location of the tube dictates the next surgical steps. For tubes placed in the anterior chamber, a sclerotomy is made 1–2 mm posterior to the limbus using a needle or blade to enter the anterior chamber and the tube is placed through the sclerotomy incision with or without placement of viscoelastic through the sclerotomy. Sulcus placement may be desired in those with pseudophakia, abnormal irido-corneal anatomy, or shallow anterior chambers.14 For sulcus placement, a sclerotomy is made 3.5 mm posterior to the limbus aiming toward the ciliary sulcus. In pseudophakic patients, the pupil is dilated to allow for proper visualization. Pars plana tube placement may be desired in aphakic patients or patients at high risk for anterior chamber complications.15 In this case, concomitant vitrectomy is often performed and the tube can be inserted through a vitrectomy port incision or a sclerotomy 3.5 mm posterior to the limbus into the vitreous cavity.

Several methods have been described to cover the tube after placement including scleral, corneal, or a pericardial patch graft or a partial thickness scleral flap. For the former, graft material made of donor sclera, cornea, or pericardium is secured to cover the length of the tube between the plate and the sclerotomy typically using absorbable sutures.16 For the latter, a 4 mm square-shaped half thickness trabeculectomy flap is created and carried anteriorly to the limbus and the sclerotomy is made beneath the scleral flap to enter the sulcus or anterior chamber. The trabeculectomy flap suture is then sutured with a non-absorbable suture. The intraocular pressure is adjusted to a physiologic level. The conjunctiva is typically sutured close with an absorbable suture.

Anti-Fibrotics During Glaucoma Drainage Device Implantation

One major reason for long-term GDD failure is thought to be related to plate encapsulation and fibrosis ultimately limiting aqueous outflow and IOP control. To address this, many surgeons will use an anti-fibrotic agents during GDD implantation. The most commonly used agent is Mitomycin C (MMC), which is an alkylating, anti-tumor agent which inhibits DNA synthesis. This can be administered by an injection or placement of sponges soaked in MMC and much of practice patterns is derived from the trabeculectomy literature.17,18 For example, a survey of the American Glaucoma Society found that 31% of surgeons indicated that they administered MMC via an injection (not sponges) during trabeculectomy.5 A study published by our group looking at GDD implantation demonstrated that subconjunctival injections of 0.1 ml of MMC (0.25 mg/ml) injected intraoperatively, at 1 and 4 weeks after Ahmed glaucoma drainage device implantation resulted in a lower incidence of the postoperative hypertensive phase.19

Surgical Outcomes After Glaucoma Drainage Device Surgery

Tube shunt surgery effectively controls glaucoma. Surgical outcomes have been reported in several retrospective and prospective studies. The five-year pooled data analysis of the Ahmed Baerveldt Comparison (ABC) Study7 and the Ahmed Versus Baerveldt (AVB) Study20 provide a comprehensive summary of two large, randomized controlled trials (RCTs) on the two most-commonly used glaucoma drainage devices (GDDs) with long-term follow-ups.21 In this study, a total of 514 adult patients with uncontrolled glaucoma were randomized to receive an Ahmed implant-PF7 (n = 267) or Baerveldt implant BG 101–350 (n = 247). At 5 years, mean IOP was significantly higher in the Ahmed group (15.8 ± 5.2 mmHg) than in the Baerveldt group (13.2 ± 4.7 mmHg), while IOP in both groups was significantly decreased from baseline mean preoperative IOP (31.5 ± 11.3 mmHg calculated from the whole study population). At 5 years, mean number of glaucoma medications was also significantly higher in the Ahmed group (1.9 ± 1.5) than in the Baerveldt group (1.5 ± 1.4), while both groups were significantly decreased from the preoperative mean number of glaucoma medications (3.3 ± 1.1). Visual outcomes were similar between the two groups. The cumulative failure rate at 5 years was higher in the Ahmed group (49%) than in the Baerveldt group (37%). High IOP was the most common reason for failure in both groups, and de novo glaucoma surgery was required more in the Ahmed group (the Ahmed group versus the Baerveldt group: 16% versus 8%:). Failure due to hypotony occurred less in the Ahmed group (the Ahmed group versus the Baerveldt group: 0.4% versus 4.5%). This pooled RCT study showed that eyes implanted with the Baerveldt GDD had a lower failure rate, lower rate of de novo glaucoma surgery, and lower mean IOP on fewer medications, though there was a slightly higher risk of hypotony compared with eyes implanted with the Ahmed GDD.

Visual Acuity After Glaucoma Drainage Device Surgery

Short-term Postoperative Visual Acuity Recovery

Visual acuity recovery after GDD surgery has been examined in a retrospective study of 375 adults who underwent Ahmed GDD implantation and were followed for 6 months postoperatively.22 The worst corrected visual acuity (CVA) occurred at 1 week postoperatively and mean CVA returned to the preoperative level by postoperative month 3. Approximately 40% of patients had some level of CVA loss compared with preoperative vision, and 9.3% of patients had 3 or more lines of CVA loss at month 6 postoperatively. Postoperative antimetabolite injection was associated with a lower risk of 3 or more lines of postoperative vision loss. The most common causes of significant vision loss were preexisting ocular conditions and cataract progression.

Long-term Postoperative Visual Acuity Recovery

Long-term visual acuity has also been evaluated in randomized clinical trials. In both the ABC and AVB Studies, there was a significant decrease in best corrected visual acuity (BCVA) in both groups during the five year follow-up period.7,20 In the ABC Study, at five years, BCVA was decreased by two or more lines from baseline in 36 (42%) patients in the Ahmed group, which was not significantly different from 38 (44%) patients in the Baerveldt group. The most frequent causes of vision loss during follow-up period were glaucoma, retinal disease, and anterior segment pathology. In the ABC Study, 96% of patients who progressed to no light perception vision were diagnosed with neovascular glaucoma.

Visual Field Changes After Glaucoma Drainage Device Surgery

Tube Versus Trabeculectomy (TVT) Study23 evaluated postoperative change in visual field following GDD surgery. Sixty-one eyes in the Baerveldt 350-mm2 implant group had 5-year visual field data analyzed. Baseline mean deviation (MD) was −13.07± 8.4 decibels (dB) and the MD rate of change was −0.60 dB/year. This rate of change in MD was comparable to that seen in eyes undergoing trabeculectomy in this trial. Baseline factors associated with more rapid visual field loss included a history of diabetes, elevated IOP, and worse preoperative MD.

In another retrospective interventional case series, visual fields from 106 eyes of 95 patients were followed for 3 years. Mean IOP was reduced from a mean of 23.1 ± 8.5 mmHg to 12.7 ± 3.1 mmHg at 3-year follow-up. Over this time period, MD, pattern standard deviation (PSD), and global Collaborative Initial Glaucoma Treatment Study score of pattern deviation probability (CIGTS_PDP) showed no significant, whereas global CIGTS score of total deviation probability (CIGTS_TDP) showed mild progression from 10.7 to 12.8 at 3-year follow-up. Pre-operative number of glaucoma medications was associated with worsening on CIGTS_TDP.

Risk of Glaucoma Drainage Device Failure

A pooled analysis of 3 prospective multicenter, randomized controlled trials was conducted to include 276 eyes from the ABC Study, 238 from the AVB Study, and 107 from the tube group of the TVT Study.21 Patients were randomized to treatment with an Ahmed glaucoma valve (model FP7) or Baerveldt glaucoma implant (model 101–350). In this pooled analysis, the cumulative probability of failure after GDD surgery was 38.3% after 5 years. In multivariable analyses, baseline factors that predicted GDD failure included preoperative IOP (≤ 21 mmHg compared to IOP > 21 and ≤ 25 mmHg), neovascular glaucoma, randomized treatment (for Ahmed glaucoma valve), and age (for 10 year decrease in age). It concluded that lower preoperative IOP, diagnosis of neovascular glaucoma, Ahmed glaucoma valve implantation, and younger age were associated with GDD failure.

Complications Following Glaucoma Drainage Device Surgery

In the ABC trial, late complications (beyond 3 months) developed in 56 subjects (46.8 ± 4.8 5-year cumulative % ± SE) in the Ahmed group and 67 (56.3 ± 4.7 5-year cumulative % ± SE) in the Baerveldt group out of 276 adult patients. The cumulative rates of serious complications were 15.9% and 24.7% in the Ahmed and Baerveldt groups, respectively, which was statistically significantly higher in the Baerveldt group. This was mainly because that Baerveldt group had more participants who experienced tube occlusion compared with the Ahmed group. Both groups had a relatively high incidence of persistent diplopia (12%) and corneal edema (20%), even though 50% of those with corneal edema had pre-existing corneal pathology. The incidence of tube erosion was significantly higher in the Baerveldt group (3%) compared with the Ahmed group (1%).

The Primary Tube Versus Trabeculectomy (PTVT) Study24 reported overall lower complication rates during the study’s 5 year follow-up period. Of the 125 study participants implanted with the Baerveldt (101–350), early postoperative complications within 3 months of surgery occurred in 24 patients (19%). Late postoperative complications developed in 27 patients (22%). Serious complications leading to vision loss and/or requiring a reoperation were observed in 3 patients (2%).

Corneal Decompensation Following Glaucoma Drainage Device Surgery

Progressive corneal endothelial cell loss (ECL) is a vision-threatening complication of GDD surgery which can require complex care and additional surgery including corneal transplantation.25 A healthy corneal endothelium is essential to maintain good visual acuity and corneal clarity. While age-related ECL in healthy eyes is on average 0.6% per year,26 several studies have shown that GDD implantation with the tube placed in the anterior chamber (AC) can lead to 6–15% ECL at 12 months and 11–18% at 24 months.27–29 In a prospective cohort study, ECL after GDD implantation was reported to be 36.8% at 5-year follow-up.30 This progressive ECL can lead to corneal decompensation, which has been reported to occur in 9–27% of eyes after GDD implantation with an average of 3-year follow-up.31,32 This number is even higher for patients with preexisting corneal pathology. For example, in patients with prior corneal transplantation, corneal decompensation rate has been reported as 45% three years following GDD implantation.33

Although ECL after GDD surgery is most likely a multifactorial process, mechanical damage to the corneal endothelial cells due to the silicone tube is likely the most significant and modifiable mechanism. Other proposed mechanisms for ECL include altered aqueous humor composition, preoperative elevated IOP directly compressing endothelial cells, anti-glaucoma medications, preservative toxicity, iris-related ECL, and endothelial growth over the tube.34

Placement of the GDD tube into the sulcus has advantages over tube placement in the vitreous cavity and is a promising alternative to AC tube placement in GDD implantation. An interventional study on a cohort of pseudophakic patients with glaucoma following Ahmed GDD implantation showed that the mean monthly ECD loss in the sulcus placement group (106 eyes from 101 patients) was significantly lower than that in the AC placement group (105 eyes from 94 patients; 15.3 cells/mm2 versus 29.9 cells/mm2).35 Future well-designed randomized controlled trials are still necessary to determine the optimal tube location to preserve corneal function and prevent ECL.

Conclusion

In summary, GDD surgery has gained popularity as a one of the most commonly performed incisional glaucoma surgeries for patients with medically uncontrolled glaucoma. Multiple large RCTs have demonstrated both efficacy and safety. With the increased rate of GDD implantation, future research is needed to examine surgical approaches, improve device design, and study long-term surgical outcomes.

Acknowledgments

This work was supported by funding from the National Eye Institute (NEI, P30 EY002162) - Core Grant for Vision Research, and by an unrestricted grant from Research to Prevent Blindness, New York, NY. This work was also supported by funding from the NEI (UG1EY033703) to Dr. Ying Han.

Footnotes

The authors report no financial interest in the subject matter of this paper.

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