Transcription:
Collaborations and Controversies: Minimally Invasive Glaucoma Surgery (MIGS)

Melanie Cole (Host): Welcome to Better Edge, a Northwestern Medicine Podcast for Physicians. I'm Melanie Cole today we're discussing collaborations and controversies in minimally invasive glaucoma surgery or MIGS. Joining me in this panel is Dr. Angelo Tanna. He's the Vice Chair in the Department of Ophthalmology, the Director of the Glaucoma Program, and a Professor of Ophthalmology at Northwestern Medicine.

Dr. Mingy Kang. She's an Assistant Professor of Ophthalmology at Northwestern Medicine and Dr. Brenda Bohnsack. She's the Division Head in Pediatric Ophthalmology at Lurie Children's Hospital and the Cowen Reiger Research Professor of Pediatric Ophthalmology at Northwestern University Feinberg School of Medicine.

Doctors, thank you so much for joining us and Dr. Tanna, I'm going to let you take it from here.

Angelo P. Tanna, MD (Guest): So, let's start by talking about minimally invasive glaucoma surgery, which is the topic of this podcast. So, this was a term that was coined about 10 years ago and has since evolved. Others have now started calling it microinvasive glaucoma surgery. And for the purposes of this discussion, we're going to limit the conversation to the types of operations that do not result in a bleb. So, there are new operations that are available now, for example, with the XEN Gel Stent and the newer InFocus device that allow for transconjunctival and subconjunctival filtering of aqueous humor. But we're going to focus our discussion on operations that take advantage of the existing outflow pathway and do not result in the formation of a bleb.

So, primarily operations in which there is excision of the trabecular meshwork and inner wall of Schlemm's canal or placement of a device that either stents the canal, such as the Hydrus or bypasses the trabecular meshwork, such as the iStent. So, Mingy in thinking about these operations, which patients do you think benefit most from minimally invasive glaucoma surgical approaches?

Jessica M. Kang, MD (Guest): I'm generally thinking about MIGS procedures for patients with mild to moderate glaucoma and patients who also need cataract surgery. Because many of these devices are only approved in conjunction with cataract surgery. So, those are the broad categories that I'm thinking about.

Dr. Tanna: So, Mingy why not patients with severe glaucoma, why only mild to moderate glaucoma?

Dr. Kang: So I think, the evidence isn't really there for patients with severe glaucoma. I think in very small certain populations, I might consider adding a MIGS in severe glaucoma. For example, if someone with severe glaucoma needs a cataract surgery. They're pretty well controlled on their current drops, but would like to get off some drops.

I might consider something like a KDB, but in general, it's not the first thing that I reach for if I need IOP control in a severe glaucoma patient. I just don't think you get enough of a lowering. And then of course, all these procedures are going to be limited in the amount of IOP lowering that you get, because they're not bypassing the episcleral venous pressure as well.

Dr. Tanna: So, by KDB you mean the Kahook Dual Blade what I call excisional goniotomy and what's interesting, the success rate for the GATT procedure, that's the procedure in which you use a microcatheter or suture to go all the way around Schlemm's canal. And then you pull the suture or microcatheter into the anterior chamber, thereby opening the canal for 360 degrees.

The failure rate for that operation in patients with severe glaucoma, which was defined as a mean deviation, worse than negative 15 decibels was 80% at six months. I completely agree with you that these minimally invasive procedures and by the way, I'd call that one maximally invasive among all the minimally invasive procedures, don't really work well in patients with severe disease.

Brenda you've been working in the angle for your entire clinical career because you're a pediatric glaucoma specialist. Why is it, do you think that these procedures don't work well in adults with severe glaucoma?

Brenda L. Bohnsack, MD (Guest): I'm sure it comes down to the pathology. In kids, as you said, angle surgery has been our mainstay for 50, 60 years. We've been doing goniotomies and trabecholotomies more in the traditional way for, especially for primary congenital glaucoma, since the sixties, easily. And that's an interesting question because what we know from the pediatric world is that especially in primary congenital glaucoma, trabeculectomies and goniotomies have a success rate anywhere from 60 to even 90%, depending on which studies you're reading and stuff. And certainly many of these kids have in quotes, severe glaucoma, but I think it comes down to the pathogenesis of the glaucoma, meaning that the kids who have this form of glaucoma, that is very amenable to angle surgery, it's because of an inherent trabecular meshwork, dysfunction, meaning that the trabecular meshwork did not develop properly. In adults, it's a very different situation because it's not that the trabecular meshwork didn't develop properly and that the trabecular meshwork itself may be working, you know, mostly okay. But there's other factors at hand that are prominent in adults, but not in children. So, I think it all comes down to the pathophysiology of the reason why the pressures are high.

Dr. Tanna: Yeah, I agree completely, especially for the distinction between success of angle surgery in children compared to adults, but in adults with severe disease, with severe visual field damage, that is, I think it's very likely that because of the advanced stage of the disease process in those patients, that the downstream pathways such as the collector channels are also diseased, such that bypassing the trabecular meshwork doesn't solve the problem necessarily.

The other reason, I think the failure rate was so high with the GATT procedure in patients with severe disease is partly an artifact of the fact one needs a lower intraocular pressure in those patients. And so they're more likely to have more surgery. For example, if their pressure was only 20 millimeters of mercury, whereas in somebody with mild disease, 20 millimeters of mercury might be just fine.

So, Mingy, which MIGS procedures do you like to use and which ones do you think ophthalmologists should have in their toolkit? Do you need a variety of procedures available in order to be able to help the most number of patients and provide this alternative option?

Dr. Kang: I do think it's nice to have a variety, and sort of tailor it based on the patient. But I don't think you necessarily need to use all the MIGS that are available. I personally prefer using the Hydrus over the iStent for more mild or mild, moderate glaucoma. I think there's increasing data to support that the Hydrus is more effective.

And so I also think it just makes sense, that you're opening up a larger area of the trabecular meshwork, as opposed to two or three pinpoint areas with the iStent. So, I typically prefer, using the Hydrus and then for more squarely, moderate glaucoma, as opposed to mild moderate, I would consider an excisional goniotomy. But in these patients, I really prefer to have them off any anticoagulants, including baby aspirin. And I also am hesitant to do them in monocular patients because of the high risk of hyphema and how debilitating it can be during the postoperative period to have blurry vision while you're waiting for this hyphema to clear in you're only seeing eye. So, those are some considerations I take into account.

Dr. Tanna: Yeah, that's a great point, Mingy and I agree with you about this distinction between the Hydrus and the iStent, with the Hydrus seeming to be more effective, based on a limited number of studies, including one by the way, that compared Hydrus to iStent directly in a head-to-head clinical trial.

Let me ask you first, Brenda, do you use excisional goniotomy with the Kahook Dual Blade in your practice at all?

Dr. Bohnsack: Me personally, I have not. There's been limited data as to whether there's any advantage of an excisional versus a traditional incisional goniotomy in childhood glaucomas. I've seen a little bit of preliminary data from a few groups. And I think a lot of it has to do with the fact that traditional goniotomy, and when I say traditional goniotomy, it's either done with a blade or I just use a 25 gauge needle, is cheap and quick and has a very high success rate as I already mentioned. And the added expense of a KDB has really not been shown to give significant improvement or significant increase in success rates. So, until I see further data saying that it's worth the extra cost, I have not converted to that form of goniotomy.

Angelo P. Tanna, MD (Guest): And Mingy, how about you other than the stent device that you prefer, the Hydrus, what are your thoughts about either GATT or Kahook Dual Blade excisional goniotomy? Do you use those procedures?

Dr. Kang: I will. Yes. KDB. I will say that I feel like in at least in the adult literature, there's not, and Brenda, you can correct me if I'm wrong, there's not as much evidence suggesting that unlike in peds, where if you get more degrees, you get a better result. I don't think that's been as clearly outlined in the adult literature. And I honestly just prefer a KDB because I find it easier than using a GATT. But I don't think either is a bad choice for the more moderate glaucoma patient.

Dr. Tanna: Well, that's a really interesting point that you bring up and I have to tell you I’ve heard some preliminary data that was done using a biomedical engineering model. So, we have a graduate student at Northwestern named Nicholas Farar, who worked with Mark Johnson, who is an outflow expert at Northwestern. And what they did was they did a study in which they modeled the resistance to outflow through both the meshwork and through the collector channels. And what they found in their engineering model was that 90 degrees of excision of the trabecular meshwork and inner wall of Schlemm's canal, close to maximized the outflow that you can achieve using some sort of a excisional approach.

So, your observation, that you reach your maximum at about 90 degrees is very much in line with the engineering hydrodynamic model that was proposed by those two. So, very interesting concurrence between your clinical impression and an engineering model. I think that's fascinating. The other interesting finding from that study, was relevant to the iStent Inject. So, as you know what the iSten Inject, the surgeon places two separate outflow devices through the trabecular meshwork into Schlemm's canal. And the other observation from Mark Johnson and Nicholas Farar's study was that to optimize the advantage of having two stents, having them three clock hours apart maximized outflow. So, you don't need to go beyond that, which it's technically more difficult to have them more widely spaced than that. So, that's an interesting pearl too.

Dr. Bohnsack: That's interesting. I wonder if there's differences between the pediatric population and the adult population? Certainly I think 90 degrees of cleft in the trabecular meshwork can certainly maintain a good pressure control. And I have a number of kids who have less than 90 degrees of cleft and they're doing fine. But at least in terms of the pediatric data, there is some thoughts or some indications that the larger the cleft, the better the success, and that may be for a number of different reasons. One could easily be that we do know that clefts tend to, I would say close, but, they can certainly decrease in extent over time.

And so if you have more than 90 degrees open, if you have 180 or 360 degrees open, then you just have more cleft that you can lose before you lose your success. The other thing on that too is, and we recently published a paper on this is that certainly with like the GATT procedure or the traditional AB Exturno trabeculotomy still using the microcatheter and doing 360 degrees. If you can get the catheter at 360 degrees and in children, much less so than in adults, that's not always a given because the trabecular meshwork anatomy itself can be very abnormal that you tend to have a higher success rate with 360 degrees. But that may be a little bit of a self fulfilling prophecy, because if you can get the catheter around 360 degrees, then the trabecular meshwork and the Schlemm's canal anatomically is probably more normal in those situations.

And so maybe more amenable to angle surgery in the first place, then an eye that's not amenable to a 360 degree trabeculectomy. It, it's an interesting contrast and I'm not sure, if it's a difference between kids and adults or if the aqueous humor dynamics are still the same, but it's just a matter of almost like time of followup.

Dr. Tanna: Well, I wonder Brenda, whether in children in primary congenital glaucoma, what you're really doing is you're allowing the trabecular meshwork and inner wall to reset its, its architecture, perhaps. So, there's probably more of a regenerative process at play, I believe in children, in whom you're doing goniotomy or trabeculotomy, whereas in adults, I think you're literally just opening up, physically opening up the structure and there probably isn't a regenerative process that kicks in. What are your thoughts on that?

Dr. Bohnsack: Certainly we know that the angle structures are not fully developed until at least four to six months of age, and so certainly when doing angle surgery in kids younger than four to six months of age, because the natural process there is that the trabecular meshwork and the angle structures are continuing to develop, I agree there very well could be remodeling. And kind of, as you said, resetting the system. With that said, even after six months of age, though, I can go back and still see the cleft that I created when the child was two months old. So, it's not that the cleft disappears.

And certainly when looking at these kids' angles later on, you can see that the cleft is still there in eyes that still have good pressure control and you can see certainly increased scarring or loss of the cleft in angles where the pressures are going up. So, I'm not sure it's exactly one-to-one type of situation, but I think that doesn't make sense in children compared to adults.

Dr. Tanna: Yeah it's interesting, you know, we can see the cleft in adults who had primary congenital glaucoma and underwent trabeculectomy. So, even patients in their thirties, forties, and fifties, I can still see the cleft. But the question is what is the tissue that's there that may not be visible to the naked eye. Do you think that there's something akin to trabecular meshwork that's present in that cleft?

Dr. Bohnsack: That's a good question. We really don't know with the idea that of the trabeculotomy and that the trabecular meshwork would be removed, with the trabeculotomy process, is it a wide open pathway from the anterior chamber straight to Schlemm's, or is there some sort of remodeling in some form maybe primorial of trabecular meshwork? I honestly don't know. And it, it's an interesting pathology question. And if we ever can specifically look at that in eyes, that'd be an interesting thought.

Dr. Tanna: Let's give our listeners some surgical pearls that they can take home. So, Brenda, you've been doing a lot of angle surgery in children, and I'm sure that you have pearls that you could share with us that would enhance our surgical success rates and make the surgery more efficient to perform. When it comes to goniotomy, what are your recommendations? What do you think translates to adult glaucoma surgical management?

Dr. Bohnsack: Well, that's an interesting question because I, I deal mostly in the vast majority of what I deal with is childhood glaucomas. I think as far as goniotomy is concerned, it's all about technique and the view. There's definitely a technique component to it, making sure that where you're incising the trabecular meshwork, I shoot for more the anterior trabecular mesh work. But there's definitely a learning curve to it, meaning that needing to be in the right place. And also there's a feel to it too, especially when doing it with a knife or with a needle. I'd be curious as to whether there's also the similar type of feel when doing it with a KDB. I've also used the 360TRAB or the 360Visco device, a handful of times too. It's a little harder to manipulate inside the anterior chamber because of how large it is. But with that device, you can get 360 degrees, through the goniotomy incision. And so it can be a good option, especially in eyes where you have a good view. And it can be just as quick as a regular goniotomy and certainly quicker than an AB-interno GATT.

Dr. Tanna: Thank you Brenda and Mingy how about you?

Dr. Kang: As far as surgical pearls, I think, talking to the patient pre-op I think it's important to manage their expectations and make sure that they know they might still be on some drops after the procedure and we're not looking for a drastic IOP lowering. I think also it's good to just give them a heads up that we will be turning their head during the surgery, since the patients are awake. Just so that they know what to expect and make sure that they don't have any limitations in their neck movements. And then as far as during the surgery, everyone talks about getting a good view. And I think it's really important not just to have a clear and like in focused view, but really making sure that the trabecular meshwork is on FOSS.

So, meaning it's not tilted away from you, but you can really see it almost as if it were like a flat surface in front of you, as opposed to being tilted. So, just making sure the patient's head is rotated as much as you need it to be as well as the scope being rotated as, as much as you need it to be.

Dr. Tanna: Yeah, having a perfect view is absolutely key. I completely agree. So, you know, I would add one thing, which is that the distal outflow pathway, the post canalicular outflow pathway appears to be most important in the infranasal region. So, trying to target the infranasal region as much as possible, I think is helpful. I think surgeons should be able to have two tools at their disposal. You know, some sort of a stent or Hydrus device and either GATT or the dual blade to perform a goniotomy. And with the GATT another pearl is that you really don't have to go 360 degrees in order to be successful. So, people are talking about Hemi GATT these days, where you pass the catheter or suture 180 degrees, for example, and then retrieve the suture after a cutdown.

So, I think these sorts of newer approaches are going to prove to be more important, especially when we better understand the patients in whom these are most likely to be successful. I certainly agree, mild to moderately severe glaucoma is the place where these surgeries have their best appeal, at least in adults, of course. And we need more clinical trials comparing these procedures, head to head so that we can start to develop a better understanding of what surgeries are best for our patients. Thank you both for being part of this. I really appreciate your insight. And your participation. Thank you.

Host: Thank you so much doctors for participating in this lively discussion today. To refer your patient, or for more information, please visit our website at nm.org to get connected with one of our providers. That concludes this episode of Better Edge, a Northwestern Medicine Podcast for Physicians. Please remember to download, subscribe, rate, and review this podcast and all the other Northwestern Medicine Podcasts. I'm Melanie Cole.