Aqueous Shunts for the Treatment of Glaucoma

Jeffrey A. Tice, MD

Disclosures

CTAF 

In This Article

Technology Assessment (TA)

TA Criterion 1: The Technology Must Have Final Approval From the Appropriate Government Regulatory Bodies. The FDA has approved the following aqueous shunt devices: Ahmed glaucoma valve implant(New world Medical Inc.), Molteno implant (Molteno Ophthalmic Ltd.), Baerveldt glaucoma implant (Abbott Medical Optics Inc.), Krupin-Denver vale implant (Hood Laboratories, Inc.), and Ex-PRESS Mini Glaucoma Shunt (Alcon). The Solx DeepLight Gold Micro-Shunt (OccuLogix) and the EyePass Glaucoma Shunt are still in Phase III of clinical trials and has not received FDA approval at this time.

TA Criterion 2: The Scientific Evidence Must Permit Conclusions Concerning the Effectiveness of the Technology Regarding Health Outcomes. The Medline database, Embase, Cochrane clinical trials database, Cochrane reviews database and the Database of Abstracts of Reviews of Effects (DARE) were searched using the key words "shunt," "drain," "tube," "device," "implant," "ahmed," "baerveldt," "krupin," "molteno," "optimed," "schocket," "express," or "solx." The results were crossed with the results from a search on "glaucoma." The search was performed for the period from 1945 through May 2011. The bibliographies of systematic reviews and key articles were manually searched for additional references. References were also solicited from the manufacturers and local experts. The abstracts of citations were reviewed for relevance and all potentially relevant articles were reviewed in full. This review focuses on the randomized comparisons between aqueous shunts of different designs and between the shunts and surgical trabeculectomy, the current standard surgical treatment. There is an extensive observational literature documenting the feasibility and safety of lowering IOP with aqueous shunts. However, outcomes clearly vary by patient characteristics including the underlying cause for glaucoma, the history and type of prior surgery, patient age, diabetes, and the presence of cataracts. Randomized trials are essential to evaluate the comparative effectiveness of aqueous shunts, particularly when there are many alternative therapies available.

The search identified 1214 potentially relevant studies (Figure 1). After elimination of duplicate and non-relevant references including reviews and non-randomized studies the search identified 28 articles describing 23 trials. The most important set of trials compare aqueous shunts to trabeculectomy, the current standard for patients with an indication for an aqueous shunt. Additional randomized trials either evaluated adjuncts to the standard shunt procedure or compared two different shunts.

Figure 1.

Selection of studies for inclusion in review

TA Criterion 3: The Technology Must Improve Net Health Outcomes. The most important outcomes for patients include preservation of vision (visual acuity, peripheral vision) and quality of life. Secondary outcomes of importance include control of intraocular pressure and the number of medications used to control IOP. Studies of glaucoma use a wide variety of definitions for success and qualified success. Complete success is usually defined as an IOP ≤ 21 mm Hg and ≥ 6 mm Hg on no medications a year following surgery. A qualified success is the same degree of pressure control, but on medications. The World Glaucoma Association also suggests reporting results using two lower IOP cutoffs: 18 and 15 mm Hg.[40] Unfortunately, almost every trial used a slightly different definition for success and failure making comparisons across trials problematic. The complications associated with aqueous shunts include early hypotony, capsule fibrosis leading to increased IOP and thus clinical failure, visual loss, tube or plate erosion, diplopia, strabismus, corneal decompensation, and infection.[41,42]

There are a large number of case series evaluating devices that shunt aqueous humor from the anterior chamber of the eye to decrease IOP.[43–55] They demonstrate the long term safety and efficacy of Molteno shunts for up to ten years[47] and the Ahmed device up to seven years[52,55] There are also a number of retrospective and prospective comparative studies.[56–71] Some evaluated variants in techniques for shunt implantation,[60,61,66] some compared different shunt devices,[56,59,68,69,71] and others compared aqueous shunts to trabeculectomy or other techniques for controlling IOP.[57,58,63–65,67,70]

The randomized trials are described in more detail below.

Technical Approaches to Aqueous Shunt Surgery

Several early randomized trials evaluated adjuncts to surgery to see if they improved outcomes. Valimaki and colleagues randomized 22 patients undergoing implantation of a single plate Molteno shunt to treatment with oral prednisolone for ten weeks in order to control bleb fibrosis.[72] Systemic corticosteroids did not improve outcomes and are no longer used. Two other randomized trials evaluated the benefits of adding mitomycin C to aqueous shunts, one with a Molteno shunt[73] and one with an Ahmed shunt.[74] Neither trial found any benefit to the addition of mitomycin C and it is rarely used today. The Latin American Glaucoma Society investigated the utility of performing a partial Tenon's capsule resection when implanting an Ahmed shunt for neovascular glaucoma.[75] Adding partial Tenson's capsule resection did not improve outcomes or reduce complications. Finally, there was one small trial that randomized twenty eyes to an Ahmed shunt with or without pericardial membrane with a goal of reducing the post-operative hypertensive phase by expanding the surface area of the endplate.[76] They found that expanding the endplate decreased the incidence of the hypertensive phase to 20% compared to 80% in the control group (p=0.007) with a trend towards fewer patients requiring medications to maintain their target IOP.

Aqueous Shunts versus Surgical Trabeculectomy

The observational data established that aqueous shunt devices could lower IOP with a reasonable complication rate and that they are well tolerated in the eye for up to ten years. However randomized trials are required to control for potential selection bias, measurement bias, and residual confounding in the observational studies. Trabeculectomy is the accepted alternative treatment to lower IOP in the population of patients refractory to medical and laser therapy. It is the ideal comparator for studies evaluating the efficacy of aqueous shunts.

Ahmed Glaucoma Valve versus Trabeculectomy Study The first randomized trial to compare an aqueous shunt device (Ahmed Model S-2) to trabeculectomy was performed in Sri Lanka and Saudi Arabia.[77] Some of the patients from the hospital in Sri Lanka were included in a second study that reported three year outcomes.[78] In order to not count patients twice, this technology assessment will primarily focus on the second study because it is larger and has a longer follow-up. In brief, the first study found that participants in the Ahmed group had higher mean IOP and required more glaucoma medications, but otherwise had similar results and complications.

The second study was performed at one site in Sri Lanka with all surgeries performed by one surgeon. Patients with either primary open angle glaucoma or chronic angle closure glaucoma were eligible for randomization. Exclusion criteria included other forms of glaucoma, prior intraocular surgery, lack of light perception, age less than four years, and eyes requiring additional surgical interventions.

All patients were treated as randomized: 59 to the Ahmed group and 64 to the trabeculectomy group, although the reported numbers differ in the two publications describing the study results. The mean age of the participants was 52 years and 67% were female. The mean preoperative IOP was 25.9 mm Hg in the Ahmed group and 26.9 mm Hg in the trabeculectomy group. None of the baseline characteristics differed significantly between the two groups.

There were no significant differences between the two groups in visual fields or visual acuity at any of the seven time points assessed except for improved visual field scores for the Ahmed group at two years. This may have been a reflection of multiple statistical testing, but the trend favored the Ahmed group at every time point. For the first year, IOP was higher in the Ahmed group, but the curves came together from 18 months through three years. From two to two and a half years, the average IOP was 13.1 mm Hg in the Ahmed group and 14.2 mm Hg in the trabeculectomy group. The cumulative probability of success during the two to two and a half year time frame was 73.2% in the Ahmed group and 72.1% in the trabeculectomy group.

Post-operative complications were similar in the two group (p>0.28 for each of the nine classes of complications). The most common complications were a flat anterior chamber (15% in both groups), hyphema (17% versus 11%,), corneal drying (14% versus 8%), and wound leak (3% versus 9%). Implant or tube exposure occurred in 5% of patients in the Ahmed group. There were only two cases of persistent hypotony and both occurred in the trabeculectomy group. There were nine repeat surgeries in each group. The Ahmed group required repeat surgery for elevated IOP (n=4), repositioning of the tube (n=2), and intervention for an exposed tube (n=3). The trabeculectomy group required repeat surgery for elevated IOP (n=2), bleb revision (n=2), blebitis (n=1), and repair of a wound leak (n=4). Cataract surgery was performed for 5 patients in the Ahmed group and 11 patients in the trabeculectomy group (p not reported).

In summary, the study demonstrated that the Ahmed shunt and trabeculectomy had equivalent preservation of vision and control of IOP through two years with equivalent complication rates, though the types of complications varied. However, the methodological quality of the study was questionable. A computer-generated list of random numbers was used for group assignment, but apparently no allocation concealment was used so selection bias cannot be ruled out. In addition, neither the surgeon nor the patients were blinded, so measurement bias is possible. The use of mitomycin C in the trabeculectomy group was optional and 9% of patients were not treated with the anti-metabolite therapy that is now standard. Follow-up was incomplete as seven patients in the Ahmed group and six patients in the trabeculectomy group did not return for follow-up after discharge from the initial hospitalization, and less than 50% of each group had three years of follow-up. Larger, multicenter, multi-surgeon studies are needed to ensure the robustness of these results.

Tube versus Trabeculectomy Study The Tube versus Trabeculectomy (TVT) Study is a large, multicenter study comparing the safety and efficacy of a non-valved aqueous shunt (Baerveldt 350 mm2) to surgical trabeculectomy with mitomycin C in patients with prior intraocular surgery.[79–84] Patients were eligible for inclusion if they were between the ages of 18 and 85 years, had inadequately controlled glaucoma with IOP ≥ 18 mm Hg and had undergone prior surgery (trabeculectomy, cataract surgery, or both). Exclusion criteria included pregnancy, no light perception, active proliferative retinopathy, recurrent uveitis, severe blepharitis, or the need for combined surgery or additional ophthalmic surgical procedures. Randomization was stratified by clinical center and prior surgical type. Allocation concealment was not described. The primary outcome measure was IOP. Important secondary outcomes were the rates of complications including bleb related infections and persistent post-operative diplopia. Failure was defined as any of the following four criteria: IOP > 21 mm Hg or not reduced by 20% on two consecutive follow-up visits; IOP ≤ 5 mm Hg on two consecutive follow-up visits; additional glaucoma surgery; or loss of light perception. The outcome of complete success was defined as a participant who did not fail and was not requiring supplemental medical therapy. Planned follow-up is five years.

Between October 1999 and April 2004, the 17 study centers randomized 212 participants (n=107 to the tube group; n=105 to the trabeculectomy group).[83] All participants received their assigned treatment. There were no significant differences in age (mean 71 years), sex (53% female), race (45% White, 39% Black, 14% Hispanic), or diabetes (32%). There were also no differences in the ocular characteristics of the participants including the eye operated on (53% left), IOP (25.3 mm Hg), number of glaucoma medications (3.1), prior laser therapy (52%), underlying diagnosis (81% primary open-angle glaucoma), or type of prior surgery (44% prior cataract extraction, 56% prior trabeculectomy).

The one and three year results have been published[81,82] and the five year results should be available within the next year. There were no significant differences in serious operative complications, though trends favored the tube group. Intraoperative complications tended to be less common in the tube group (7% versus 10%, p=0.59). Significant post-operative complications in the first year, defined as those requiring reoperation and/or a loss of at least two lines of visual acuity on a Snellen chart, also tended to be less common in the tube group (17% versus 27%, p=0.12). Post-operative complications were significantly less common in the tube group (34% versus 57%, p=0.001), but most of these were self-limited. Two individual complications were significantly less common in the tube group: corneal dysesthesia (1% versus 7%, p=0.034) and wound leaks (1% versus 11%, p=0.004). There was a trend toward more persistent diplopia in the tube group (5% versus 0%, p=0.06). A new or worsened motility disturbance of the eye (strabismus) was more common in the tube group (9.9% versus 0%, p=0.005).[84] At one year there was no difference in IOP (12.4 mm Hg in tube group versus 12.7 in the trabeculectomy group, p=0.73), but the average number of glaucoma medications used was higher in the tube group (1.3 versus 0.5, p<0.001) and IOP was significantly higher in the tube group during the first three post-operative months. Complete success was less common in the tube group (34% versus 63%, p < 0.001). However, failures were also less common in the tube group (3.9% versus 13.5%, p=0.017). The reasons for failure were inadequate IOP control (4 in tube group, 10 in trabeculectomy group) and persistent hypotony (0 in tube group, 3 in trabeculectomy group).

At three years there was also no difference in IOP (13.0 mm Hg in tube group versus 13.3 in the trabeculectomy group, p=0.78) and the average number of glaucoma medications used was no longer significantly higher in the tube group (1.3 versus 1.0, p=0.30). Significant post-operative complications through three years also did not differ between the two groups (22% versus 27%, p=0.58). Complete success was less common in the tube group (28% versus 40%, p = 0.10). However, failures were also less common in the tube group (15.1% versus 30.7%, p=0.010). At three years, the reasons for failure were inadequate IOP control (7 in tube group, 10 in trabeculectomy group), persistent hypotony (2 in tube group, 8 in trabeculectomy group), reoperation for glaucoma (6 in tube group, 9 in trabeculectomy group), and loss of light perception (0 in tube group, 1 in trabeculectomy group). Although none of the subgroup differences were statistically significant, the trend favored the tube group in all subgroups.

The TVT study is the largest randomized trial to directly compare an aqueous shunt tube to surgical trabeculectomy. Follow-up was excellent with only 10% of visits missed during three years of follow-up. All patients received their allocated treatment and strict intention-to-treat was used for all analyses. Methodologically, it was not perfect because the participants and providers were not blinded, which may have biased the assignment of complications and the decision to reoperate. However, measurement bias in studies with objective outcomes tends to be less significant than in studies with subjective outcomes.[85] In response to this criticism, the investigators published data demonstrating a trend in the opposite direction: the mean IOP at the time of reoperation was 21.5 mm Hg in the tube group and 27.9 mm Hg in the trabeculectomy group (p=0.12).

When comparing the results of the TVT study to other studies, it is important to keep in mind the population studied. All of the participants in the TVT study had undergone at least one prior ocular surgery, but patients with conditions predisposing them to surgical failure (neovascular glaucoma, iridocorneal endothelial syndrome) were excluded. Thus, patients were at higher risk for complications than surgically naïve patients, but at lower risk than many of the patients included in the early case series and comparative studies of aqueous shunts, which often included patients at high risk of failure following trabeculectomy.

Both operations continue to evolve. In the TVT study, trabeculectomy was performed using a limbus-based conjunctival flap. Recent trends suggest that trabeculectomy performed using a fornix based flap with diffuse rather than focal application of mitomycin C may be preferred.[86] In addition, only one type of aqueous shunt was used: the Baerveldt 350. Many other devices are in use or in development. The results of the TVT study may not generalize to other aqueous shunts.

Through three years, participants randomized to the Baerveldt aqueous shunt group had fewer short-term complications (34% versus 57%), fewer failures (15% versus 30%), but more diplopia (5% versus 0%) and more strabismus (9.9% versus 0%). The failure rate in the tube group was lower than that estimated by a recent meta-analysis,[41] but the patients randomized came from a lower risk group. Overall, the evidence from the TVT study suggests that the Baerveldt aqueous shunt is at least equivalent to trabeculectomy in this patient population.

Ex-PRESS versus Trabeculectomy Several case series reported that the Ex-PRESS shunt, a newer stainless steel aqueous shunt, was safe and effective at lowering IOP[44,45,49,50,53] except when performed using the older, subconjunctival technique.[54] Additional comparative studies suggest that the lowering of IOP and the reduction in use of glaucoma medications achieved with the Ex-PRESS shunt were equivalent to trabeculectomy with fewer complications (hypotony, choroidal effusion, hyphema).[57,58,64,67,87] The two randomized trials comparing the Ex-PRESS device to trabeculectomy are described below.[88–90]

In this single center study by a single surgeon, 80 eyes from 78 patients were randomized to either the Ex-PRESS shunt or trabeculectomy.[90] Patients were eligible for the study if they were ages 18 and older with open angle glaucoma that was inadequately controlled with medical therapy. Exclusion criteria included any other ocular disease and previous ocular surgery other than cataract extraction. Complete success was defined as a final IOP > 4 mm Hg and ≤ 18 mm Hg without medication. Overall success was defined by the same criteria with or without medication. Failure was an IOP > 18mm Hg or the need for additional glaucoma surgery. The more typical definition of failure (recurrent surgery, loss of 2 lines of Snellen visual acuity; or IOP out of range) was not reported for either group.

There were 40 eyes in each group. The Ex-PRESS group was significantly younger (62.3 years versus 68.9, p=0.03) and there was a trend towards more female participants in the Ex-PRESS group (52.5% versus 32.5%, p= 0.11). The mean preoperative IOP was 22.8 mm Hg in the Ex-PRESS group and 21.5 mm Hg in the trabeculectomy group (p=0.34). There were no significant differences in IOP at one year (approximately 12 mm Hg in the Ex-PRESS group and 13 mm Hg in the trabeculectomy group) or in the number of medications used (0.3 versus 0.6, p not reported except non significant). The proportion of patients achieving an IOP ≤ 18 mm Hg at one year was greater in the Ex-PRESS group (84.6% versus 60%, p=0.023). However, the success rate with or without medications did not differ between the two groups (97% versus 87%, p=0.20). Visual acuity declined in 13.5% of patients in the Ex-PRESS group who returned for the one year visit and in 15.8% of the trabeculectomy group (p not significant). There were 13 complications in the Ex-PRESS group (32.5%) and 11 complications in the trabeculectomy group (27.5%). Early hypotony with a shallow anterior chamber was the most common complication. Complications requiring surgical intervention were identical (5% in each group).

The five-year results demonstrated continued good control of IOP in both groups (11.5 versus 11.3 m Hg, p NS). There were no significant differences between the groups in the percentage of patients with successful control of IOP (≤ 18 mm Hg) without medications (59% versus 46%, p=0.25) or with medications (97.4% versus 100%, p=0.49). The use of glaucoma medications was similar in the two groups at five years (0.85 versus 1.10, p not reported), but the number was increasing in the Ex-PRESS group, while decreasing in the trabeculectomy group. The Ex-PRESS group experienced fewer complications requiring needling (3 versus 9) and fewer cataract surgeries (5 versus 8), but no statistical analysis was reported. No data on repeat glaucoma surgeries or loss of vision were reported. There was also no reporting of any loss to follow-up or deaths.

There are many methodological issues with this trial. It was a relatively small trial, so estimates of event rates would have wide confidence intervals. In addition, the confidence intervals were not reported. As in most trials of aqueous shunts, there was no blinding of the investigator or the patients, which may have introduced some bias in decisions about medication use or other interventions. The significant baseline differences in age and sex call into question concealment of the randomization sequence generated by the computer. Only a handful of baseline characteristics were reported in Table 1 and follow-up was incompletely reported. Because a single surgeon performed all procedures in this study, the results may reflect his personal skill set and may not be generalizable beyond his practice. This study suggests that the Ex-PRESS device may be equivalent to trabeculectomy in the population studied for at least five years, but a larger multicenter study with better reporting is required in order to convincingly demonstrate that conclusion.

The second trial randomized 30 eyes from 15 patients to either the Ex-PRESS shunt or to trabeculectomy and followed for an average of 24 months.[88] Patients over the age of 18 years with primary open angle glaucoma who required bilateral surgical treatment were eligible. Patients with other forms of glaucoma and active uveitis were excluded. One surgeon performed all of the procedures. Complete success was defined as IOP > 5 mm Hg and < 18 mm Hg without glaucoma medications. The average age of the participants was 65 years, 33% were female, 40% Black, 33% Indian, and 20% Caucasian. The baseline IOP was 28.1 mm Hg in the Ex-PRESS group and 31.1 mm Hg in the trabeculectomy group (p=0.48) with an average of 3.7 medications used by each group. Prior surgeries for glaucoma had been performed on 67% (10/15) of the eyes in each group. One patient died after 13 months of follow-up and two were lost to follow-up. IOP decreased to 15.7 mm Hg in the Ex-PRESS group and to 16.2 mm Hg in the trabeculectomy group (p NR). Post-operative use of glaucoma medications were similar (0.3 versus 0.9, p NR). The complete success rate was greater in the Ex-PRESS group (~77% versus ~28% estimated from Kaplan-Meier plot at 24 months, p=0.002). Complications were less common in the Ex-PRESS group (20% versus 33%, p=0.05) as were complications requiring surgical intervention (0% versus 27%, p=0.001). The most common complication was hypotony (7% Ex-PRESS group, 33% trabeculectomy group), but all resolved spontaneously and without serious complication within one month of surgery.

In this small, single surgeon randomized trial, the Ex-PRESS shunt showed a reduction in IOP similar to that achieved with trabeculectomy, but with fewer complications and fewer patients requiring medications to maintain target IOP.

Randomized Trials Comparing Devices

Single-plate versus Double-plate Molteno Shunt One of the earliest randomized trials of aqueous shunt devices compared the single-plate Molteno shunt to the double-plate Molteno shunt to evaluate whether the greater surface area of the double endplant improved outcomes through a greater reduction in IOP.[91] Between March 1988 and February 1990, the study randomized 132 patients who had a poor surgical prognosis with trabeculectomy. The average pre-operative IOP was 34.8 mm Hg. Allocation concealment was preserved until the patient was in the operating room. The primary outcome was IOP ≤ 21 mm Hg and ≥ 6 mm Hg with no additional glaucoma surgeries and no devastating complications. At one year, the success rate was 55% in the single-plate group and 86% in the double-plate group. At two years, the success rate was 46% in the single-plate group and 71% in the double-plate group. The difference in success rates between groups was statistically significant (p=0.0035). The average reduction in IOP was 25% for the single-plate group and 46% for the double-plate group (p=0.01). Visual acuity loss of at least two Snellen lines was also more common for the single-plate group (27% versus 20%, p NR). There was less post-operative hypotony in the single-plate group resulting in fewer flat anterior chambers (4% versus 10%, p=0.25) and fewer choroidal hemorrhages or effusions (0% versus 8%, p=0.043). The remaining complications were uncommon and there were no significant differences between the groups, but the difference favored the single-plate shunt.

In summary, the increased surface area of the double-shunt increased the success rate in patients with poor surgical prognosis. However, there was also an increase in early hypotony and other complications. Surgical techniques and medical therapy have evolved significantly in the twenty years since the study was performed, so the results may not apply today.

Double-plate Molteno versus Schocket Procedure Another early randomized trial of aqueous shunt devices compared the double-plate Molteno shunt to the anterior chamber tube shunt to encircling band (ACTSEB) procedure developed by Schocket.[92] This was a small randomized trial of 40 eyes with all procedures performed by a single surgeon between 1987 and 1989. Post-operative IOP at two years was similar in the two groups (14.4 mm Hg Molteno, 15.0 mm Hg ACTSEB,p=0.74), but the Molteno group required more medications (0.95 versus 0.43, p=0.024). Surgical interventions for complications or inadequate IOP control was high in both groups, but less common in the Molteno group (47% versus 57%, p NR). Visual acuity decreases of two lines or more on the Snellen chart were also less common in the Molteno group (32% versus 52%, p NR). These results may reflect the skills of a single surgeon and the number of eyes randomized was low, so the results may not be generalizable. Furthermore, the surgeries were performed more than 20 years ago: medical therapy, surgical techniques and the devices have changed significantly in the interim. In view of these limitations, this trial suggests that the Molteno shunt provides equivalent control of IOP to that of ACTSEB with at least a trend towards fewer complications and less loss of vision.

Baerveldt 350 versus Baerveldt 500 A larger study randomized 107 patients between 1991 and 1993 to the Baerveldt shunt with a 350 mm2 endplate or a 500 mm2 endplate.[93,94] The goal was to evaluate whether the greater surface area led to greater reductions in IOP and higher long-term success rates similar to those reported in the single-plate versus double-plate Molteno trial.[91] The average pre-operative IOP was 30.5 mm Hg. Success was defined as IOP ≤ 21 mm Hg and ≥ 6 mm Hg with or without additional medication. Failure was defined as IOP > 21 mm Hg on two consecutive visits, additional glaucoma surgery, loss of light perception or IOP < 6 mm Hg. At one year, the success rate was 98% in the 350 mm2 group and 92% in the 500 mm2 group. At two years, the success rate was 93% in the 350 mm2 group and 75% in the 500 mm2 group. Even though the median follow-up was only about 36 months, the investigators reported results out to five years. At five years, the success rate was 79% in the 350 mm2 group and 66% in the 500 mm2 group. The difference in success rate was statistically significant at all time points. The overall failure rate was 13% in the 350 mm2 group and 30% in the 500 mm2 group (p=0.05). The mean IOP at 2 years was 13.2 mm Hg in the 350 mm2 group and 12.3 mm Hg in the 500 mm2 group (p=0.41). Visual acuity loss of at least two Snellen lines was similar in the two groups (50% versus 54%, p 69). There were no significant differences in the complication rates between the two groups during any year of follow-up, though there were slightly more complications in the 500 mm2 group.

This study found that the 350 mm2 Baerveldt shunt had a greater success rate through five years of follow-up with a trend towards fewer complications and fewer failures. As with the prior studies, this study was performed almost 20 years ago, so the results may not generalize. However, it clearly demonstrated that there was no advantage to increasing the area of the endplate beyond 350 mm2. Of note, the Molteno single plate device had an area of approximately 130 mm2 and the double plate had an area of 270 mm2.

The Ahmed Baerveldt Comparison Study The recently published early results from the Ahmed Baerveldt Comparison (ABC) Study are important because they allow for direct evaluation of the comparative effectiveness of a valved aqueous shunt (Ahmed) and a non-valved aqueous shunt (Baerveldt 350) in the modern era of glaucoma management.[95,96] The size of the end plate is another major difference between the two devices (184 mm2 for the Ahmed Device and 350 mm2 for the Baerveldt device), so the trial is not strictly a comparison between a valved and non-valved device. Prior observational studies have not conclusively defined the relative benefits and harms of the two devices.[59,68,71,97,98] They are the two most commonly used aqueous shunts in the United States and glaucoma surgeons divided in their opinion about the preferred device.[96]

Patients were eligible for inclusion in the ABC study if they were between the ages of 18 and 85 years, had inadequately controlled glaucoma with IOP ≥ 18 mm Hg and had an aqueous shunt as their planned surgery. Exclusion criteria included lack of light perception, prior aqueous shunt implantation, prior cyclodestructive procedure, uveitis associated with systemic illness like juvenile rheumatoid arthritis, the need for combined surgery or additional ophthalmic surgical procedures, or if they lived at a distance and would be unavailable for follow-up. Randomization was stratified by surgeon within clinical center and type of glaucoma. Allocation concealment was not described. The primary outcome measure was the success rate where success was defined as not failing. Failure was defined as any of the following five criteria: IOP > 21 mm Hg or not reduced by 20% on two consecutive follow-up visits; IOP ≤ 5 mm Hg on two consecutive follow-up visits; additional glaucoma surgery; removal of the implant; or loss of light perception. The sample size for the study was based on the results from a comparative study in Singapore that reported a 67% success rate for the Ahmed shunt and an 83% success rate for the Baerveldt shunt.[98] Important secondary outcomes were the rates of complications including hypotony, tube occlusion, macular edema, endophthalmitis, cataract, diplopia, corneal edema, and tube or shunt erosion. Planned follow-up is five years.

Between October 2006 and April 2008, 16 centers randomized 286 participants, but ten participants withdrew consent prior to surgery. The publications only report data on the remaining 276 participants (n=143 in the Ahmed group; n=133 in the Baerveldt group).[95] Two participants in each of the groups received a device other than their assigned treatment. However, all analyses were performed according to randomization in adherence with strict intention-to-treat principles. There were no significant differences in age (mean 64 years), sex (49% female), race (49% White, 25% Black, 12% Hispanic, 12% Asian), or diabetes (41%). There was a trend towards older participants in the Ahmed group (65 versus 62 years, p=0.053) and significantly more patients with hypertension in the Ahmed group (63% versus 50%, p=0.039). There were also no differences in the ocular characteristics of the participants including the eye operated on (46% left), IOP (31.5 mm Hg), number of glaucoma medications (3.4), or the underlying diagnosis (40% primary open-angle glaucoma, 29% neovascular, 7% uveitic, 7% primary angle closure glaucoma, 18% other).

The one year results have been published.[96] The three and five year results should be published in the future. There were no significant differences in intraoperative complications, though trends favored the Ahmed group (8% Ahmed versus 11% Baerveldt, p=0.31). Intraoperative complications were primarily of hyphemas (22/28 = 79%). Significant post-operative complications in the first year, defined as those requiring reoperation and/or a loss of at least two lines of visual acuity on a Snellen chart, also tended to be less common in the Ahmed group (20% versus 34%, p=0.12). Any early post-operative complication in the first three months was also less common in the Ahmed group (43% versus 58%, p=0.016), but most of these were self-limited. Two individual complications were significantly less common in the Ahmed group: corneal edema (12% versus 22%, p=0.035) and tube occlusion (2% versus 9%, p=0.015). Diplopia was similar in the two groups (6% versus 5%, p=0.80) as were tube erosions (1 in each group). At one year IOP was higher in the Ahmed group than the Baerveldt group (15.4 mm Hg versus 13.2, p=0.007), and the average number of glaucoma medications also tended to be higher in the Ahmed group (1.8 versus 1.5, p=0.071). The rate of failures at one year was similar using the primary outcome definition of failure as an IOP > 21 mm (16.4% versus 14%, p=0.017). The reasons for failure in the Ahmed group were inadequate IOP control (n=20) including 11 who required reoperation, loss of light perception (n=2), but no one with persistent hypotony. The reasons for failure in the Baerveldt group were inadequate IOP control (n=7), including 1 who required reoperation, loss of light perception (n=6), and persistent hypotony (n=2). The one year failure rate was significantly higher in the Ahmed group for the strictest definition of failure: IOP > 14 mm Hg (38.6% versus 24.0%, p=0.008).

Thus, through one year of follow-up, there is no clearly preferred aqueous shunt. Participants in the Baerveldt group had lower IOP, tended to need fewer medications, had fewer reoperations for inadequately controlled IOP, and tended to have fewer failures, but they also had significantly more serious complications and significantly more reoperations for complications. The results from continued follow-up through three to the planned five years will better define the comparative effectiveness of these two devices.

Ahmed versus Molteno There is one additional recent comparative trial, though it is relatively small and had poor follow-up. Between 2003 and 2005, the study randomized 92 patients from three centers in Iran to the Ahmed shunt or the Molteno single-plate shunt. Patients with poorly controlled IOP despite maximally tolerated medications or who had failed prior surgery were eligible for randomization. The exclusion criteria were age less than 40 years, no light perception, cataracts, prior drainage device implantation, prior cyclodestructive surgery, active ocular infection, or immunosuppression. The primary outcome measure was IOP. Failure was defined as IOP > 21 mm Hg on two consecutive visits, additional glaucoma surgery, shunt removal, loss of light perception, any major complication, or IOP < 6 mm Hg.

The study sample had a mean age of 61 year, 49% were female, and the pre-operative IOP was 32 mm Hg. There were no significant differences between the two groups at baseline. Follow-up was poor: only 75% of the sample were available for analysis at one year and only 62% were available at two years. At two years, the mean IOP was higher in the Ahmed group (17.0 versus 15.4, p<0.001), although the Ahmed group was using fewer glaucoma medications (1.0 versus 1.4, p NS). There were no differences in the changes in visual acuity between the two groups. The failure rates were similar through two years (16% Ahmed, 18% Molteno, p=0.65).

The relatively small sample size and the high loss-to-follow-up rate make it difficult to draw any firm conclusions from this study. In addition, the IOP levels achieved after surgery were significantly higher than those reported in other studies.

Comments

3090D553-9492-4563-8681-AD288FA52ACE

processing....