Lecture: Glaucoma Drainage Devices: Techniques and Decision Making

This lecture covers:
• Rationale for using glaucoma drainage devices
• Types of glaucoma drainage devices
• Indications
• Surgical techniques
• Comparative Studies
• Recommendations

Surgery location: on-board the Orbis Flying Eye Hospital in Yaoundé, Cameroon

Lecturer: Dr. James Brandt, University of California, Davis


(To translate please select your language to the right of this page)

DR BRANDT: So this talk is a very comprehensive review of glaucoma drainage devices. And we have about 45 minutes. And I could take this talk out to two hours, if we wanted to. I won’t do that to you, because I don’t want to keep you from getting home. So I will skip through some areas, to get to the most important parts. So what we’re gonna cover is the rationale for using glaucoma drainage devices. The types of glaucoma drainage devices. The indications. The surgical techniques, which I will skip over mostly, because you saw some good videos. You saw a live surgery. And then we’ll talk about some of the important clinical trials that have been done to compare glaucoma drainage devices to trabeculectomies. Now, glaucoma drainage devices were developed because we all know that trabeculectomies tend to fail over time. And trabeculectomies sometimes fail very quickly, in the first few days to months after a trabeculectomy. Or they fail late and very slowly, over many months to years. If trabeculectomies fail early on, in the first few days, the things we worry about are that the trabeculectomy is blocked by something like iris or vitreous, and if the trabeculectomy fails in the first few months, it’s usually because of scarring of the conjunctiva and Tenon’s capsule, down to where the trabeculectomy was performed. Trabeculectomies fail later due to slow but relentless continuous fibrosis. They can also fail because of infections, and this is — I’m sure you will recognize — as a patient who developed a bleb infection. This was a young man that I performed a trabeculectomy on when he was about a young teenager. Probably about 12 years old. And he disappeared and then came back about 10 years later, with an infection like this. We were able to save the eye, but his vision was very, very poor. The risk factors for a trabeculectomy failing include the things that you see here, such as a previous trabeculectomy that failed, other types of surgeries that involve the conjunctiva, and that would include prior extracapsular cataract surgery, as well as small incision cataract surgery, when you take the conjunctiva down. Also, younger patients are more likely to have trabeculectomies fail over time. Probably because they have a more robust scarring and healing process. Risk factors for late failures include aggressive use of antimetabolites. And these lead to very thin blebs that can develop leaks later on, that lead to bacteria getting inside the eye and leading to an infection, like you saw in the picture. Also patients who have poor hygiene or the ones that have bad lid disease, or who have to wear contact lenses. These are all risk factors for the patients developing an infection of a trabeculectomy, sometimes many years after the trabeculectomy was done. So glaucoma drainage devices are designed to overcome two of the problems with trabeculectomies. The silicone tube portion of the implant prevents closure of the fistula, and the external plate, which you saw me install, prevents the scarring of the conjunctiva and Tenon’s capsule down to the sclera. Putting a simple tube into the eye does not work. People have tried to do this for over 120 years. Because putting a tube in the eye, if it is a big tube, leads to a flat chamber. And the problem is that the tube, as you can see on the right of this picture — eventually the sclera, the conjunctiva, will scar down and close the opening up. So the key to these devices is a tube that diverts aqueous humor to an external reservoir. And the earliest of the glaucoma drainage implants is the Molteno implant, which is still used in many places in world. So there are two basic types of glaucoma implants. They are the non-valved implants, such as the Molteno implant, the Baerveldt implant, and I don’t have it on here, but I should — which is an implant called the AADI implant. And the AADI implant is a copy of the Baerveldt. And it is made by the Aravind Eye Hospital system in India. It’s an excellent implant. And it only costs about $50. So I would encourage you to think about having your hospitals order the AADI implant. And I can give you some of the information about getting it. Because it’s a very cost-effective way to do glaucoma implant surgery. The valved implants — the only one that is available commercially worldwide is the Ahmed implant, which you saw me put in today. The non-valved implants require you to close the tube, because if you just put the tube into the eye, the pressure will go to zero, so what we do is we implant everything, but we tie a stitch around the tube, so that enough scarring will develop around the plate, so once flow starts going through the system, after the stitch dissolves, the pressure drops to a safe range. There are advantages and disadvantages to each of these approaches. And we recently completed two clinical trials, comparing the implants. And the two implants get similar pressures. The Baerveldt probably requires less medicines after many years, but they are more difficult to implant. This is the Ahmed implant, which you saw me implant today. And this uses a valve to drop the pressure — in theory, at least — to about 10 millimeters of mercury. And the advantage of this is we do not need to tie the tube off. The pressure goes down immediately. And we put the implant in only one quadrant of the eye. It’s generally a somewhat faster surgery. The potential disadvantages of the valved implants is they’re a little smaller, and that means that the bleb is smaller and the pressure is a little higher. And at least theoretically, the capsule that develops around the implant is thicker, because of inflammation, with these devices. So the indications for these devices include failed trabeculectomy, patients with extensive scarring of the conjunctiva, possible need for more eye surgery. For example, a patient who has a cataract, but has a very, very high pressure, or is gonna need a corneal transplant. If you put in a glaucoma drainage implant, you can control the pressure, and your surgery months later will not cause the glaucoma surgery to fail. If you do a trabeculectomy and successfully control somebody’s pressure, but then do a corneal transplant or cataract surgery, the trabeculectomy is very likely to fail. Let’s talk a little bit about the techniques. You see that I tend to do a limbal-based incision. And I showed you earlier today how important it is to flush the valve, to make sure that it works well. Trim the tube to an appropriate length. And the tube can be placed under a scleral flap. Under donor tissue. Such as the pericardium you saw earlier today. Or through a long scleral tunnel. This is a baby, a 4-week-old, in whom we did a circumferential trabeculotomy. And that failed. And so we immediately took the baby back, and we performed an implantation of a glaucoma valve. So you saw much of this earlier today. So here is the tube being flushed. For those of you joining us on Cybersight, you may not have seen this. So here I’m pushing, and soon the fluid will come through, and that frees up the valve, so that it can be implanted. This is the Baerveldt implant, which is much larger, as you can see. I use a muscle hook to hold the superior rectus muscle. As you can see, it is very flexible. And now I’m going to take a muscle hook again for the lateral rectus muscle. And this is designed to sit in exactly the right place under the lateral and superior rectus muscles. And here you can see the other technique that I was describing, that I tend not to use anymore. But this is much simpler. And we use a needle to enter the anterior chamber. I explained earlier, while I was doing the surgery — and in the interests of time, I’ll skip through this — but we compared at our institution limbus-based versus fornix-based, and found no difference in the type of the incision. So if there’s no difference, why not do the way that most people do? And the answer is the ocular surface. Many of the patients have had multiple surgeries, and their ocular surface is very sick, because much of the conjunctiva has been destroyed over time. I’ll just try to go through this. This is… We’ll show you some techniques, similar to what you saw today. So here goes an Ahmed implant. This is almost exactly what you saw today. Using 8-0 nylon suture. And here is the technique that I used with the… That very small blade. Here is a Baerveldt implant going in. I’ll try to go through this a little quicker here. And you can see that this is the Baerveldt, which has not yet been tied off. Now, this is a combined procedure, in a young woman with aniridia. And I’ve taken out her cataract and put a lens in. And now I am using the needle to enter the eye. And here you can see the tube. In this case, I used Tutoplast, a pericardial graft, to cover her tube, because in the aniridia patients, they frequently have — the conjunctiva will melt away. So I wanted to have as much protection as possible. And this is what she looked like after the surgery. You can see that she has a lot of aniridia keratopathy. Which I would have made much, much worse, if I had taken the conjunctiva down. But you can see with red reflex that she has a reasonable view. And she went from around 20/400 to about 20/60. Which was a big improvement for her. And we could finally see her nerve, after about 10 years. And we had protected her optic nerve from much damage. So let me skip forward here. The postoperative care. Yes?

>> To be sure not to cut the fiber of the muscles, we have to be (inaudible)…

DR BRANDT: You just need to know the anatomy and go between the anatomy. Sometimes you might want to use a marking pen to mark where you see the muscles, so that you know where to stay away. Also, if you’re not sure where the muscles are, you can sweep with the muscle hook to loop the muscles, and that way you know — you can see directly where they are, and stay away from them. I have cut muscles, but just a little bit. They bleed. And once you do that once or twice, you’ll avoid it, because you don’t want to do that. You should never cut off a muscle. And again, this is the postoperative care, about which we discussed during the talk earlier. Now, there are some comparative studies, and there are two major prospective randomized clinical trials. Which I got to participate in. One was the tube versus trabeculectomy study. And the other one was the primary tube versus trabeculectomy study. And this slide is wrong. The one-year results were announced about 10 months ago. And our paper on the one-year results should appear sometime this spring. But I’ll share these results with you. So the tube versus trabeculectomy study compared trabeculectomy to the Baerveldt glaucoma implant in patients who had risk factors for trabeculectomies to fail. So these are patients who had prior trabeculectomy or prior cataract surgeries. And this was a prospective, randomized clinical trial. And we engaged 212 patients. These were adult patients. And they had pressures between 18 and 40. And they had the risk factors for having a trabeculectomy fail. And in the interests of time, I can share with you the TVT papers. And you can see that we started with 212 patients, and at five years, we had about 70 patients in each group that were still alive or still being followed. So at five years, you can see that the pressures are about the same. And the likelihood of the surgery failing was higher in the trabeculectomy group than in the tube group. So you can see at the end of five years, about 48% of the trabeculectomies had failed at five years. Whereas about 28% or 30% of the tubes had failed. And these are different ways of calculating failure or success, but in all of the ways that we did this, the trabeculectomies failed more than the tubes. Now, you’ll see that in terms of taking medicines, if your goal in doing surgery is to get the patient’s pressure under control without needing to use medicines, in the first two years, you can see that trabeculectomy patients needed fewer medicines. But glaucoma goes on for many, many years. And if you follow the patients out to five years, there’s no difference between the trabeculectomy and the tubes in terms of the number of medicines they have to take. So after five years, the Baerveldt implant was more likely than trabeculectomy — was more likely to maintain pressure control, to avoid too low a pressure, to avoid a necessity to do more surgery for glaucoma, or have other bad complications. I’ll skip through the complications. But I feel strongly that the glaucoma drainage devices are a very important and proven option for the surgical management of glaucoma. And although the implantation of glaucoma devices requires different skills, they are not particularly difficult, and an experienced eye surgeon can learn this pretty quickly. And at my institution, my residents probably do more tubes than they do trabeculectomies. In part, because I feel that I can keep my resident from causing — having complications with a tube than I can with a trabeculectomy. And based on the tube versus trabeculectomy, the pressure control appears to be the same after five years, between the two procedures. And I would emphasize to you that repeating the trabeculectomy, if it’s the only thing you can do, gives you diminishing returns, if you do a second trabeculectomy, a third trabeculectomy. Each time it’s less and less likely to work. And something that’s very applicable to you here in Cameroon is that tubes do not require as much postoperative care. You don’t have to adjust the sutures, inject 5FU, and all the maneuvers that we do with trabeculectomies, to make them work. So I frequently do tubes as the primary surgery for patients who live many hours and hours away. Say it’s an elderly patient whose family needs to bring them to the office. And they can’t come in every week. I will do a tube in that situation. So I recommend glaucoma drainage devices, tubes, as primary surgery when I anticipate that the patient’s gonna have trouble keeping follow-up, if they require a contact lens, such as a patient who is aphakic, and when pressure lowering is needed urgently, to stabilize the eye, knowing that other surgeries are going to be needed. So the primary TVT study — and these are the preliminary results of the primary TVT study, which was first showed almost exactly a year ago, at the American Academy. And a group of us did this study in the United States and in England and Canada. So the study was almost identical to the TVT study. But these are patients who had no previous surgery of any kind in their eye. And so the inclusion and exclusion rules were the same, except that they had no previous surgery. And the surgery was randomized to the large Baerveldt implant versus a trabeculectomy. These are the things that we measured. And we defined failure of the procedure based on pressures greater than 21 or not lowered by more than about… By 20% from baseline. It was also considered a failure if they needed more surgery. And I’ll skip through these detailed study slides. But we took 242 patients and we completed the one-year follow-up. And you can see that we had very good retention of the patients in the study. And again, in the interests of time, this will all be in the paper that will be published sometime early next year. But the tube — the two different groups were very similar. They started with pressures of about 23 to 24. And the patients were on, on average, three medicines. And here you can see the difference in the pressures, and you can see that the trabeculectomy group achieved lower pressures than the tube did in these virgin eyes, at just one year of time. And here you can see the success rate for tubes was 80%, versus 92%. And complete success means that they reached a good pressure without any medicines. So you can see here that only 14% of the patients in the tube group had a complete success, compared to 60% in the trabeculectomy group. And here you can see the survival curve. And again, I’ll skip through it, but let’s go to the conclusions about the PTVT. Which was that this was a randomized study, comparing tubes and trabs in — as first-time surgeries. And trabeculectomies with mitomycin C had a higher success rate than tubes at one year. And they were able to do this with fewer medications, and that is the end of the talk. But let me just close by saying that that does not mean that you should only use trabeculectomies in virgin eyes, and only tubes in eyes that have had previous surgery. Because all of these patients were seen very frequently, and I believe firmly that the tubes are probably a better choice for patients who cannot come back for frequent follow-up, which I suspect is very common here. And these are only one-year results. And it will be very interesting to follow these 240 patients out to five years, to see what the long-term results are. So these are just preliminary results at this point. But I would encourage you to learn how to do glaucoma drainage devices, and the most cost-effective way of doing this would be for you in your hospital to get the AADI implant, because it’s very inexpensive. They have lots of good videos to teach you how to use them. And it can be very, very effective and very inexpensive. So with that, I will close and be happy to answer any questions you might have.

>> Here in Africa, for cataract surgery, we do small incision more frequently. So in a patient who has been placed a tube before, will he have any problem, when, if he has a (inaudible) small incision surgery?

DR BRANDT: So for that situation, I think a tube is probably much better, simply because small incision cataract surgery does require you to take down the conjunctiva, and there’s probably significant conjunctival scarring, years after surgery. Let me say that again. So I think the tube is a good operation, and probably a better operation, than a trabeculectomy, in a patient who has had a previous small incision cataract surgery. Or the patient will have it later. Yes. And for the same reason, I think that a small incision cataract surgery is more likely to cause a trabeculectomy to fail than a tube to fail. Because when you do a small incision cataract surgery, you have subconjunctival bleeding, inflammation, and all of those things will cause a trabeculectomy to scar down. We even know now that the trabeculectomies fail, even with clear cornea phaco. Even when the clear cornea phaco is done very carefully, there’s still some inflammation in the eye, and there are good studies that show that the pressure goes up 4 or 5 millimeters after phaco, a year later. We do not have good data of that question about tubes, but it is my clinical impression, and that of many other surgeons, that a tube is more likely to continue to work after cataract surgery. So I think that answers your question. Pressure does go down 2 or 3 millimeters after uncomplicated clear cornea phaco. We have good evidence of that from the Ocular Hypertension Treatment Study. The problem with that is that that effect does not last for more than a few years. And it should not — you should not depend on that to control somebody’s glaucoma. If they have real glaucoma with real damage, cataract surgery is not a glaucoma operation. So the question is a good one, which is: What is my procedure for patients with cataract and glaucoma? It depends on the severity. How far away they live. There are many, many factors involved. Sometimes, if they have very mild glaucoma, I will do just cataract surgery, just to see what pressure lowering it can achieve. But I make sure that they understand that they may need to have another operation pretty quickly. Sometimes I will do a combined trabeculectomy and cataract surgery. Sometimes I will do a combined tube and cataract surgery. It really depends on each patient. And that would be another one-hour lecture, to discuss the timing and sequencing of cataract and glaucoma surgery. I can’t give you a one-minute summary. So thank you very much for all your attention.

November 9, 2017

Last Updated: October 31, 2022

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