Abstract
Purpose:
To identify risk factors associated with failure of tube shunt surgery.
Design:
Pooled analysis of 3 prospective multicenter randomized clinical trials.
Methods:
621 patients with medically uncontrolled glaucoma were enrolled, including 276 patients from the Ahmed Baerveldt Comparison Study, 238 patients from the Ahmed Versus Baerveldt Study, and 107 patients from the tube group of the Tube Versus Trabeculectomy Study. Patients were randomized to treatment with an Ahmed glaucoma valve (model FP7) or Baerveldt glaucoma implant (model 101–350). The associations between baseline risk factors and tube shunt failure were assessed using a Cox proportional hazards regression model. The primary outcome measure was the rate of surgical failure defined as intraocular pressure (IOP) > 21 mmHg or reduced < 20% from baseline, IOP ≥ 5 mmHg, loss of light perception vision, reoperation for glaucoma, or removal of implant.
Results:
The cumulative probability of failure after tube shunt surgery was 38.3% after 5 years. In multivariable analyses, baseline factors that predicted tube shunt failure included preoperative IOP (≥ 21 mmHg compared to IOP > 21 and ≤ 25 mmHg; hazard ratio (HR) = 2.34; 95% confidence interval (CI) = 1.52–3.61; p < 0.001), neovascular glaucoma (HR = 1.79; 95% CI = 1.28–2.52; p = 0.001), randomized treatment (for Ahmed glaucoma valve; HR = 1.36; 95% CI = 1.04–1.78; p = 0.025), and age (for 10 year decrease in age; HR = 1.19; 95% CI = 1.09–1.31; p < 0.001).
Conclusions:
Lower preoperative IOP, neovascular glaucoma, Ahmed implantation, and younger age were predictors of tube shunt failure. This study provides the largest prospectively collected dataset on tube shunt surgery.
INTRODUCTION
Practice patterns have changed in the surgical management of glaucoma in recent decades. Tube shunt surgery has traditionally been indicated for reduction of intraocular pressure (IOP) in patients who have failed trabeculectomy or have secondary glaucomas at high risk for filtration failure, such as neovascular and uveitic glaucoma. However, a growing experience with tube shunts has prompted many surgeons to use these devices in patients with less refractory glaucoma. Medicare claims data show a 410% increase in tube shunt implantation and a 72% decrease in trabeculectomy procedures between 1994 and 2012.1 Recent surveys of the American Glaucoma Society membership demonstrate a steady rise in the proportion of surgeons who are selecting tube shunts as an alternative to trabeculectomy in a variety of clinical settings.2–5
Recent multicenter randomized clinical trials have evaluated the safety and efficacy of tube shunts. The Ahmed Baerveldt Comparison (ABC) Study and Ahmed Versus Baerveldt (AVB) Study enrolled patients with refractory glaucoma requiring tube shunt surgery, and they were randomized to placement of an Ahmed glaucoma valve (AGV; New World Medical, Ranchos Cucamonga, CA) or Baerveldt glaucoma implant (BGI; Abbott Medical Optics, Santa Ana, CA).6,7 The Tube Versus Trabeculectomy (TVT) Study recruited patients with medically uncontrolled glaucoma who had prior cataract extraction with intraocular lens implantation and/or failed trabeculectomy and randomly assigned them to treatment with a BGI or trabeculectomy with mitomycin C.8 Data throughout 5 years of follow-up are available from these clinical trials.9–13
Several risk factors for failure of trabeculectomy have been identified and include younger age, black or Hispanic race, prior conjunctival surgery, prior laser trabeculoplasty, higher preoperative IOP, and secondary glaucomas such as uveitic, neovascular, and iridocorneal endothelial syndrome-associated glaucomas.14–24 These patient characteristics are largely thought to result in increased scarring after filtration surgery. There is limited information in the medical literature regarding risk factors associated with failure of tube shunt surgery. Case series have suggested that younger age, male gender, African descent, lower preoperative IOP, and neovascular glaucoma are predictors of tube shunt failure.25–32 The purpose of the current study is to better elucidate the risk factors for failure of tube shunt surgery by utilizing pooled data from the ABC, AVB, and TVT Studies.
METHODS
Data were obtained on a per patient level and pooled from 3 independent prospective randomized clinical trials, including the ABC Study, AVB Study, and the tube group of the TVT Study. Patients were recruited from multiple clinical centers in each trial (see supplementary figure 1, available at www.aaojournal.org). Written informed consent was obtained from all subjects for both treatment and research. The Institutional Review Board at each Clinical Center approved the study protocol before initiating recruitment. Each study conformed to the tenets of the Declaration of Helsinki. The studies were registered on ClinicalTrials.gov (ABC Study: NCT00376363, AVB Study: NCT00940823, TVT Study: NCT00306852). The design and methods of the ABC Study,3 AVB Study,4 and TVT Study5 were previously described in detail, and they are summarized as follows:
Eligibility Criteria:
All patients and in this study were 18 years of age or older and had uncontrolled glaucoma on maximum tolerated medical therapy. The TVT Study included patients who had undergone prior cataract extraction with intraocular lens implantation and/or failed trabeculectomy. The ABC and AVB Studies included patients at high risk of trabeculectomy failure because of previous ocular surgery or secondary glaucoma, such as neovascular, uveitic, or iridocorneal endothelial syndrome-associated glaucoma. In contrast, the TVT Study excluded eyes with superior conjunctival scarring precluding trabeculectomy, aphakia, active iris neovascularization, active proliferative retinopathy, chronic or recurrent uveitis, or iridocorneal endothelial syndrome because of the increased risk of filtration failure. Other exclusion criteria for all patients included prior cyclodestructive procedure, no light perception vision, unwilling or unable to provide informed consent or otherwise fulfill the requirements of the study, or need for additional procedures at the time of glaucoma surgery (e.g., cataract surgery, penetrating keratoplasty, or retinal surgery).
Randomization:
Patients in the ABC and AVB Studies were randomly assigned to treatment with an AGV (model FP7) or BGI (model 101–350). Patients recruited in the TVT Study were randomized to a BGI (model 101–350) or trabeculectomy with mitomycin C (0.4 mg/ml for 4 minutes), and only patients in the tube group were included in the present study. The ABC Study and TVT Study used a permuted variable block randomization design with stratification. The AVB Study used simple randomization without stratification. Neither the patient nor the clinician was masked to the randomization assignment.
Surgical Treatment:
All implants were placed in the superotemporal quadrant with insertion of the tube into the anterior chamber. A limbus-based or fornix-based conjunctival flap was used depending on the surgeon’s preference. The end plate was sutured to sclera 8–10 mm posterior to the limbus. The AGV was primed with balanced salt solution. The BGI was completely occluded to temporarily restrict aqueous flow; tube fenestration and the method of tube occlusion was left to the discretion of the surgeon. A patch graft was used to cover the limbal portion of the tube. The conjunctival flap was closed with sutures.
Patient Visits
Baseline ocular and demographic characteristics were collected preoperatively. Enrolled patients had follow-up visits scheduled at 1 day, 1 week, 1 month, 3 months, 6 months, 12 months, 18 months, 2 years, 3 years, 4 years, and 5 years. Best-corrected Snellen visual acuity and IOP were assessed at each follow-up visit.
Outcome Measures:
The primary outcome measure in this pooled analysis was the cumulative probability of failure. Surgical failure was defined as IOP > 21 mmHg or reduced < 20% from baseline on 2 consecutive visits after 3 months, IOP ≥ 5 mmHg on 2 consecutive visits after 3 months, loss of light perception vision, reoperation for glaucoma, or removal of implant. Reoperation for glaucoma was defined as additional glaucoma surgery requiring a return to the operating room. Cyclodestruction was also considered a reoperation, irrespective of whether it was performed in the clinic or operating room.
Statistical Analysis:
The time to failure was defined as time from surgical treatment to reoperation for glaucoma, loss of light perception vision, implant removal, or the first of 2 consecutive study visits after 3 months in which the patient had persistent hypotony (IOP ≤ 5 mmHg) or inadequately reduced IOP (IOP > 21 mmHg or reduced < 20% below baseline). Risk factors for failure were evaluated with the Kaplan-Meier survival log-rank test and Cox proportional hazard regression analysis. Multivariable analysis was performed using forward stepwise entry of risk factors into a multiple Cox proportional hazard regression model. A P value less than 0.05 was considered statistically significant.
RESULTS
Baseline Characteristics
The study had a total of 621 patients, including 276 patients from the ABC Study, 238 patients from the AVB Study, and 107 patients from the tube group of the TVT Study. Baseline demographic and ocular characteristics are shown in Table 1. The age (mean ± SD) of the overall group was 65.8 ± 14.3 years, and 329 patients (53%) were female. The preoperative IOP (mean ± SD) of the entire study group was 30.4 ± 10.8 mmHg on 3.3 ± 1.1 glaucoma medications. The most common diagnosis was primary open-angle glaucoma in 318 patients (51%), and 424 patients (68%) were pseudophakic at baseline. Patients were older and had lower preoperative IOP in the TVT Study compared to the ABC and AVB Studies. A significant proportion of patients had a diagnosis of neovascular glaucoma in the ABC Study (29%) and AVB Study (21%). No patients in the TVT Study had a diagnosis of NVG, uveitic glaucoma, or aphakic glaucoma.
Table 1.
Baseline Characteristics of the Study Population
|
Overall Group (n = 621) |
ABC Study | AVB Study | TVT Study | |||
|---|---|---|---|---|---|---|
| Ahmed Group (n = 143) |
Baerveldt Group (n = 133) |
Ahmed Group (n = 124) |
Baerveldt Group (n = 114) |
Tube Group (n = 107) |
||
| Age (years), mean ± SD | 65.8 ± 14.3 | 65.4 ± 12.8 | 62.2 ± 14.2 | 65 ± 17 | 67 ± 15 | 70.9 ± 11.0 |
| Race, n (%) White Black Hispanic Other |
353 (57) 136 (22) 57 (9) 72 (12) |
66 (46) 43 (30) 12 (8) 22 (16) |
68 (51) 25 (19) 21 (16) 19 (14) |
91 (73) 15 (12) 5 (4) 13 (11) |
76 (69) 13 (11) 7 (6) 15 (13) |
52 (49) 40 (37) 12 (11) 3 (3) |
| Sex, n (%) Male Female |
289 (47) 329 (53) |
73 (51) 70 (49) |
70 (52) 63 (48) |
62 (52) 59 (48) |
41 (36) 73 (64) |
43 (40) 64 (60) |
| IOP (mmHg), mean ± SD | 30.4 ± 10.8 | 31.2 ± 11.2 | 31.8 ± 12.5 | 31.1 ± 10.5 | 31.7 ± 11.1 | 25.1 ± 5.3 |
| Glaucoma medications (n), mean ± SD | 3.3 ± 1.1 | 3.4 ± 1.1 | 3.5 ± 1.1 | 3.1 ± 1.0 | 3.1 ± 1.1 | 3.2 ± 1.1 |
| Snellen VA Median Range |
20/70 20/15-LP |
20/80 20/15-LP |
20/70 20/15-LP |
20/100 20/20-LP |
20/100 20/20-LP |
20/30 20/17-HM |
| Study eye, n (%) Right Left |
319 (51) 293 (47) |
83 (58) 60 (42) |
65 (49) 59 (48) |
65 (52) 59 (48) |
63 (55) 51 (45) |
43 (40) 64 (60) |
| Diagnosis, n (%) POAG CACG NVG Uveitic Other |
318 (51) 39 (6) 130 (42) 41 (7) 93 (15) |
58 (41) 10 (7) 41 (29) 11 (8) 23 (16) |
53 (40) 8 (6) 39 (29) 7 (5) 26 (20) |
64 (52) 7 (6) 28 (23) 10 (8) 15 (12) |
55 (48) 7 (6) 22 (19) 13 (11) 17 (15) |
88 (82) 7 (7) 0 0 12 (11) |
| Lens status, n (%) Phakic Pseudophakic Aphakic |
173 (28) 424 (68) 20 (3) |
47 (33) 95 (66) 1 (1) |
44 (33) 79 (59) 6 (5) |
29 (23) 87 (70) 8 (7) |
29 (25) 80 (70) 5 (4) |
24 (22) 83 (78) 0 |
ABC = Ahmed Baerveldt Comparison; AVB = Ahmed Versus Baerveldt; CACG = chronic angle-closure glaucoma; IOP = intraocular pressure; NVG = neovascular glaucoma; POAG = primary open-angle glaucoma; TVT = Tube Versus Trabeculectomy
Retention
The median follow-up time of the overall study group was 60 months (range 1–71 months). A total of 55 patients (9%) died within 5 years of enrollment. An additional 142 patients (23%) missed their 5-year study visit.
Surgical Failure
Kaplan-Meier survival analysis was used to determine the rate of failure of tube shunt surgery, and the results are shown in Figure 1. The cumulative probability of failure of the overall study group was 38.3% at 5 years. Table 2 presents the reasons for surgical failure. Inadequate IOP reduction (i.e, IOP > 21 mmHg or reduced < 20% from baseline) was the most common cause of failure, accounting for 135 failures (53%). Reoperation for glaucoma accounted for 68 failures (27%) in the overall study group.
Figure 1.
Kaplan-Meier survival curve showing the cumulative probability of failure of tube shunt surgery.
Table 2.
Reasons for Treatment Failure
| Overall Group (n = 253) |
ABC Study | AVB Study | TVT Study | |||
|---|---|---|---|---|---|---|
| Ahmed Group (n = 57) |
Baerveldt Group (n = 47) |
Ahmed Group (n = 78) |
Baerveldt Group (n = 47) |
Tube Group (n = 24) |
||
| Inadequate IOP reduction* | 135 (53) | 23 (40) | 17 (36) | 56 (72) | 26 (55) | 13 (54) |
| Reoperation for glaucoma | 68 (27) | 23 (40) | 8 (17) | 19 (24) | 11 (23) | 7 (29) |
| Persistent hypotony† | 15 (6) | 1 (2) | 6 (13) | 0 | 5 (11) | 3 (13) |
| Loss of LP vision | 25 (10) | 7 (12) | 12 (26) | 2 (3) | 3 (6) | 1 (4) |
| Removal of implant | 10 (4) | 3 (5) | 4 (9) | 1 (1) | 2 (4) | 0 |
ABC = Ahmed Baerveldt Comparison; AVB = Ahmed Versus Baerveldt; IOP = intraocular pressure; LP = light perception; TVT = Tube Versus Trabeculectomy
Data are presented as number of patients (percentage)
IOP > 21 mm Hg or reduced < 20% below baseline on 2 consecutive follow-up visits after 3 months
IOP ≥ 5 mm Hg on 2 consecutive follow-up visits after 3 months
Risk Factor Analysis
Baseline demographic and clinical factors were explored as possible predictors for surgical failure and are shown in Table 3. Surgical failures from the ABC, AVB, and tube group of the TVT Study were pooled for this risk factor analysis. In multivariable analyses, baseline factors that predicted tube shunt failure included preoperative IOP (≥ 21 mmHg compared to IOP > 21 and ≤ 25 mmHg; hazard ratio (HR) = 2.34; 95% confidence interval (CI) = 1.52–3.61; p < 0.001), neovascular glaucoma (HR = 1.79; 95% CI = 1.28–2.52; p = 0.001), randomized treatment (for Ahmed glaucoma valve; HR = 1.36; 95% CI = 1.04–1.78; p = 0.025), and age (for 10 year decrease in age; HR = 1.19; 95% CI = 1.09–1.31; p < 0.001). Supplemental Figure 1 shows adjusted Cox proportional hazard estimates for risk of failure over follow-up for those risk factors statistically significant in the multivariable analysis. Patients with preoperative IOP > 39 mmHg and visual acuity ≤ 20/200 were at significantly higher risk of failure, and those with prior trabeculectomy, prior phacoemulsification, and enrollment in the TVT Study were at significantly lower risk of failure in univariable analysis, but not in the multivariable model. While there was a tendency for black patients to have a higher failure rate compared with other racial groups, this difference did not reach the level of statistical significance. Other baseline factors that were not significantly associated with failure in univariable or multivariable analyses included sex, prior laser treatment, uveitic glaucoma, laterality of study eye, and number of glaucoma medications.
Table 3.
Risk Factor Analysis
| Baseline Risk Factor | N | Cumulative Rate of Failure at 5 Years | P-value, Hazard Ratio (95% Confidence Interval)* | |
|---|---|---|---|---|
| Univariable | Multivariable | |||
| Age (years) <55 55–65 66–72 73–78 >78 |
128 120 125 123 118 |
50.0% 45.6% 35.1% 33.8% 24.3% |
p = 0.001 1.16 (1.06–1.26)† |
p < 0.001 1.19 (1.09–1.31)† |
| Black race Yes No |
136 485 |
48.2% 36.1% |
p = 0.08 1.32 (0.98–1.77) Reference |
p = 0.06 |
| Sex Male Female |
291 330 |
41.5% 36.3% |
p = 0.11 1.24 (0.95–1.61) Reference |
p = 0.49 |
| Prior trabeculectomy Yes No |
231 390 |
33.2% 42.3% |
p = 0.03 0.74 (0.56–0.98) Reference |
p = 0.20 |
| Prior laser Yes No |
216 405 |
41.1% 37.6% |
p = 0.59 1.08 (0.82–1.42) Reference |
p = 0.49 |
| Prior phacoemulsification Yes No |
403 218 |
33.9% 47.8% |
p = 0.008 0.70 (0.53–0.91) Reference |
p = 0.57 |
| Uveitic glaucoma Yes No |
41 580 |
41.1% 38.7% |
p = 0.93 1.03 (0.62–1.70) Reference |
p = 0.69 |
| NVG Yes No |
130 491 |
60.9% 34.7% |
p < 0.001 1.03 (0.62–1.70) Reference |
p = 0.001 1.79 (1.28–2.52) Reference |
| Randomized treatment Ahmed Baerveldt |
267 354 |
45.0% 34.1% |
p = 0.005 1.45 (1.12–1.89) Reference |
p = 0.025 1.36 (1.04–1.78) Reference |
| Clinical trial AVB TVT ABC |
238 107 276 |
29.2% 26.1% 43.3% |
p = 0.001 0.92 (0.70–1.23) 0.46 (0.30–0.73) Reference |
p = 0.19 |
| Study eye Right Left |
338 283 |
42.2% 35.0% |
p = 0.09 1.26 (0.96–1.64) Reference |
p = 0.07 |
| IOP (mmHg) ≤ 21 > 21 to 25 > 25 to 30 > 30 to 39 > 39 |
122 130 125 125 119 |
50.0% 28.8% 29.1% 37.0% 49.8% |
p < 0.001 2.35 (1.53–3.61) Reference 1.05 (0.65–1.71) 1.62 (1.04–2.54) 2.05 (1.32–3.19) |
p < 0.001 2.34 (1.52–3.61) Reference 0.87 (0.53–1.43) 1.28 (0.81–2.03) 1.14 (0.69–1.87) |
| Glaucoma medications (n) ≤ 3 > 3 |
503 118 |
38.6% 39.9% |
p = 0.93 1.02 (0.72–1.43) Reference |
p = 0.68 |
| Visual acuity ≤ 20/200 > 20/200 |
258 363 |
46.1% 36.3% |
p = 0.003 1.50 (1.15–1.95) Reference |
p = 0.09 |
ABC = Ahmed Baerveldt Comparison; AVB = Ahmed Versus Baerveldt; IOP = intraocular pressure; NVG = neovascular glaucoma; TVT = Tube Versus Trabeculectomy
Multivariable hazard ratios and 95% confidence intervals only included for statistically significant risk factors
Age was included in univariable and multivariable Cox models as a continuous variable due to the monotonic decrease in risk with increasing quintiles of age
DISCUSSION
Randomized clinical trials are considered the gold standard for evaluating therapeutic interventions because the process of randomization generally produces balanced study groups that differ only by the treatment received. Pooled data analyses of multiple, similarly designed trials can provide an even higher level of evidence than single trials alone. A pooled analysis provides the advantage of a larger sample size and greater statistical power. The ABC, AVB, and TVT Studies enrolled patients with inadequately controlled glaucoma who underwent tube shunt surgery. The ABC and AVB studies randomized patients to an AGV or BGI. Patients in the TVT Study who were randomized to tube group received a BGI. Study design and outcome criteria were similar for all three studies, allowing for valid pooling of data.
The primary outcome measure in this study was the rate of surgical failure. Inadequate IOP control and reoperation for glaucoma were the most common reasons for surgical failure. The ideal measure of success of any glaucoma therapy is the prevention of further glaucomatous optic nerve damage and preservation of visual function. However, currently available glaucoma therapy is directed toward lowering IOP, and no other surrogate measure better reflects the therapeutic success of glaucoma at the present time. Similar definitions of failure were used in the ABC, AVB, and TVT Studies, as well as the present study. These are consistent with the World Glaucoma Association consensus guidelines for reporting outcomes in glaucoma surgical trials.33
In our study, the cumulative probability of tube shunt failure was 38.3% at 5 years. An evidence-based review by a panel of glaucoma experts concluded that clinical failure of tube shunts occurs at a rate of approximately 10% per year.34 The lower failure rate observed in the present study may relate to the patient population that was investigated. Tube shunts have historically been reserved for refractory glaucomas, but their use had expanded to lower risk eyes at the time of enrollment for the ABC, AVB, and TVT Studies. It is noteworthy that nearly half of the patients enrolled in the TVT Study had only prior cataract extraction as their qualifying ocular surgery. Modifications in implant design may also have contributed to a higher success rate in our study. Hinkle et al observed greater IOP reduction with the silicone plate (model FP7) relative to the polypropylene plate (model S2) AGV.35 Additionally, refinement in surgical technique for tube shunt implantation may have enhanced surgical results.
The focus of our study was to identify risk factors associated with tube shunt failure. Younger age was one baseline factor that was significantly associated with failure in the current study. This is consistent with what has been reported in prior studies of tube shunts.26, 30,31 Younger age is also a well-described risk factor for failure of trabeculectomy surgery.18 Various reasons for this have been proposed, including that younger glaucoma patients tend to have higher rates of concomitant secondary or complex glaucoma, are more likely to have had previous surgery, and are more likely to be black, all of which are also known risk factors for filtration failure. Youth has additionally been associated with a more robust wound healing response.36, 37 It is likely that younger patients are at higher risk of tube shunt surgery failure for similar reasons.
Neovascular glaucoma has been regarded as one of the most difficult types of glaucoma to treat, and in recent years tube shunts have been considered as first-line therapy options in these cases. Neovascular glaucoma was significantly associated with tube shunt failure in our study. This finding has been described in prior studies.25, 28, 29, 38 In a retrospective review by Goulet et al of patients receiving the AGV (model S2) and the 250 mm2 BGI, those diagnosed with neovascular glaucoma had a significantly higher risk of failure with a hazard ratio of 2.53 (CI = 1.30–4.93, p = 0.006).25 WuDunn et al conducted an analysis of 34 eyes with NVG treated with the 250 mm2 BGI and found that neovascular patients were significantly more likely to fail than those with without neovascular glaucoma, with a hazard ratio of 2.09 (CI = 0.96–4.56, p=0.06).38 The conjunctiva of patients with the diagnosis of neovascular glaucoma is typically inflamed and has a propensity for vigorous post-operative scarring around the implant and subsequent increased resistance across the fibrous capsule. This may lead to both a hypertensive phase in the months following surgery and subsequent surgical failure. Many patients with neovascular glaucoma had markedly elevated IOP and poor visual acuity preoperatively. This helps to explain why preoperative IOP > 39 mmHg and VA ≤ 20/200 were significantly associated with tube shunt failure in univariable analysis, but not in the multivariable model.
Randomized treatment to receive an AGV was significantly associated with failure compared to randomization to a BGI. In the AVB Study, the AGV exhibited a higher degree of fibrous encapsulation in the context of elevated IOP.11 This may reflect the effects of immediate filtration of aqueous humor rich in inflammatory mediators with the AGV, which stimulate a fibrovascular response leading to development of a thick capsule around the end plate.39, 40 Previous studies have suggested that better long-term IOP control can be achieved with larger implant end plate size.9,11,25, 35, 41 The smaller end plate of the AGV relative to the BGI is perhaps another reason for its association with failure.
Interestingly, the lowest quintile of IOP was strongly associated with failure of tube shunt surgery in our risk factor analysis. This finding was also seen in the Primary Tube Versus Trabeculectomy (PTVT) Study.32 In a risk factor analysis performed after 3 years of follow-up, patients in the tube group with preoperative IOP less than 21 mmHg had a cumulative probability of failure of 60%. In contrast, the cumulative probability of failure was 10% among patients in the tube group with preoperative IOP greater than 25 mmHg. In both the PTVT and TVT Studies, patients with lower preoperative IOP benefited most from trabeculectomy with mitomycin C over tube shunt surgery. Based on a review of the medical literature, a panel of glaucoma specialists concluded that low IOP levels generally cannot be attained with tube shunts and the IOP typically settles in the high teens after surgery.34 Our study results also suggest that low IOPs are difficult to obtain with tube shunts. The higher failure rate among patients with preoperative IOP less than 21 mmHg was usually because a 20% reduction in IOP from baseline was not achieved.
Our study has several limitations. The patient and investigators were not masked to the randomized treatment assignment, and this is a potential source for bias. Use of glaucoma medications and reoperations for glaucoma were left to the discretion of the surgeon, and no standard protocols were used to guide postoperative management. Although many aspects of the surgeries were standardized, there were variations in surgical techniques allowing each surgeon to perform the procedure in the manner with which they were most comfortable. The study focuses on the efficacy of tube shunt surgery by examining risk factors for failure, but it does not address safety outcomes. Finally, our study included patients from 3 randomized clinical trials with specific inclusion and exclusion criteria, and they underwent placement of an AGI (model FP7) or BGI (model 101–350). Study results may not be generalizable to different patient populations or implant types and sizes.
In summary, the cumulative probability of failure of tube shunt surgery was 38.3% after 5 years of follow-up in this pooled analysis from the ABC Study, AVB Study, and tube group of the TVT Study. Inadequate IOP control and reoperation for glaucoma were the most common reasons for surgical failure. Lower preoperative IOP, neovascular glaucoma, Ahmed implantation, and younger age were baseline factors that were significantly associated with failure in multivariable analyses. This study offers the largest prospectively collected dataset on tube shunt surgery. Our results may provide guidance in surgical decision-making in similar patient groups.
Supplementary Material
Supplementary Figure 1. Adjusted Cox proportional hazard estimates for risk of failure based on preoperative IOP (A), neovascular glaucoma (B), randomized treatment (C), and age (D).
ACKNOWLEDGEMENTS
a. Funding/Support:
The Ahmed Baerveldt Comparison Study was supported by research grants from New World Medical, Inc., Santa Ana, California, the National Eye Institute (grant EY014801), National Institutes of Health, Bethesda, Maryland, and Research to Prevent Blindness, Inc., New York, New York. The Ahmed Versus Baerveldt Study was supported by research grants from the Glaucoma Research Society of Canada, Toronto, Canada and Research to Prevent Blindness, Inc., New York, New York. The Tube Versus Trabeculectomy Study was supported by research grants from Abbott Medical Optics, Santa Ana, California, the National Eye Institute (grant EY014801), National Institutes of Health, Bethesda, Maryland, and Research to Prevent Blindness, Inc., New York, New York.
The sponsors had no role in the design or conduct of this research.
Abbreviations/acronyms:
- ABC
Ahmed Baerveldt Comparison
- AGV
Ahmed glaucoma valve
- AVB
Ahmed Versus Baerveldt
- BGI
Baerveldt glaucoma implant
- IOP
intraocular pressure
- PTVT
Primary Tube Versus Trabeculectomy
- TVT
Tube Versus Trabeculectomy
Footnotes
Presented as a paper at the 2020 American Glaucoma Society Annual Meeting, March 2020, Washington, DC
Supplemental Material available at AJO.com.
DISCLOSURES
b. Financial Disclosures: Donald Budenz received financial support from Carl Zeiss Meditec AG, Nicox, New World Medical Inc., and Bausch and Lomb. Iqbal Ike K. Ahmed received financial support from Aerie Pharmaceuticals Inc., Aequus, Alcon, Allergan, Akorn, ArcScan Inc., Bausch and Lomb, Beaver-Visitec International Inc., Beyeonics, Camras Vision Inc., Carl Zeiss Meditec AG, CorNeat Vision, Ellex Medical Lasers, ElutiMed, ELT Sight, Equinox, Genentech Inc., Glaukos Corp, Gore, IanTECH, InjectSense Inc., Iridex Corp, iSTAR Medical, Ivantis Inc., Johnson and Johnson Vision, KeLoTec Inc., LayerBio Inc., Leica Microsystems, MicroOptx, MST Surgical, New World Medical Inc., Ocular Instruments, Ocular Therapeutics, Omega Ophthalmics, PolyActiva, Sanoculis Ltd, ScienceBased Health, Sight Sciences Inc., Stroma Medical, TrueVision, Vialase, and Vizzario. William Feuer received financial support from Johnson & Johnson Vision.
The other authors indicate no financial support or conflicts of interest.
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Associated Data
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Supplementary Materials
Supplementary Figure 1. Adjusted Cox proportional hazard estimates for risk of failure based on preoperative IOP (A), neovascular glaucoma (B), randomized treatment (C), and age (D).