Lecture: Tips on MIGS

Learning intraoperative gonioscopy and minimally invasive glaucoma surgery (MIGS) comes with a unique set of challenges. Skills required for MIGS are surprisingly different than those required for cataract surgery or traditional glaucoma surgery. In this webinar, Dr. Provencher shares tips on intraoperative gonioscopy and various MIGS procedures in an attempt to kick start your surgical learning curve.

Lecturer: Dr. Lorraine M. Provencher, MD, glaucoma fellow and clinical lecturer at the University of Michigan Kellogg Eye Center, USA


DR PROVENCHER: All right. Hello, everyone. My name is Lorraine Provencher. I’m just finishing up my glaucoma fellowship at the University of Kellogg Eye Center, and I spent a large part of the last year learning intraoperative gonioscopy and MIGS, and I hope that I can help share some tips that I have learned along the way this year. The outline for today will include two parts. The first being intraoperative gonioscopy. We’ll go over principles, implementation, and troubleshooting. And then we’ll move on quickly to review some MIGS basics, before delving into a few of my favorite MIGS that I feel are most appropriate for a global audience. But I do want to start with some poll questions, to get to know the audience a little bit. So if you could tell me what your current level of training is. Are you a resident, a fellow, do you consider yourself a young surgeon, or an experienced surgeon? Or do you fall into some other category? Are you an optometrist, support staff, or a scrub nurse? Okay. It looks like we have a nice mixture. Some residents, some fellows, some young surgeons, and also some experienced surgeons. That’s great. We’ll go to one more poll question here. What is your experience with intraoperative gonioscopy? Have you never tried it or observed it live, have you observed it but not tried it yourself, have you tried a few cases, but are still uncomfortable, learning, or having difficulty? Are you proficient but could be better? Or are you skilled and could teach it? Okay. It looks like we have a nice mixture, again. Most people have never tried it or observed it. Some have observed it but have not tried it themselves. That’s about 60% of the audience. And the rest are the more skilled, and we don’t have those people here. So this is going to be a perfect talk for this audience. So intraoperative gonioscopy is truly a foundation of MIGS. Everything surgical that you will do is built upon your skill as a gonioscopist. I think that obtaining and maintaining an adequate view is one of the most difficult hurdles when it comes to these procedures. As we know, light from the iridocorneal angle undergoes refraction at the air-tear film interface. Hence the need for gonioscopy when it comes to viewing the angle. There are two basic types of gonioscopy, and therefore two types of gonio lenses. The direct and indirect lens. Direct lenses change the angle of light’s interface with air, so that the light from the trabecular meshwork exits more perpendicularly. And until the MIGS revolution, direct gonioscopy was reserved mostly for pedes glaucoma, during examination under anesthesia or goniotomy. And outside of the OR, we really don’t use it much, as it’s impractical in clinic. It requires a coupling agent, a portable slit lamp, and the patient has to be supine. But direct gonioscopy has made a comeback with MIGS. So I have many tips on how to get started. Some of these details may seem small or simple, but if done incorrectly, they can make an easy case seem very difficult or even impossible to complete safely. Success starts in the clinic, with proper patient selection. For direct gonio, you will need to rotate the patient’s head, so checking for neck mobility and lack of a significant head tremor is very important. The patient should also be cooperative. When working in such a small space, there is little safety net for sudden head movements, saccade, cough, et cetera. So you really need a good patient, or you need to modify your anesthesia. It’s also ideal to be able to visualize the angle in clinic. You need to identify important landmarks, ensure the intended procedure is possible, and potentially modify your technique. This is not an absolute, as the angle often widens post-phaco, so you can still do MIGS surgery, but it’s important to know what you’re getting into. There are several steps you can take as the surgeon, prior to doing your first case, that will prepare you for surgical success. I think gonio in clinic is crucial, not just for your surgical evals, but really for as many patients as you can. Comfortability with angle anatomy will serve you well in the OR. If you’re not used to doing gonioscopy in clinic, you really should not be attempting intraoperative gonioscopy. Along the same lines, you need to know your landmarks cold. Intraoperatively is not the time to be figuring out whether you’re looking at trabecular meshwork or scleral spur, ciliary body, et cetera. So really know your landmarks cold. Gonioscopy.org is a really awesome resource that was designed and created by Dr. Lee Alward at the University of Iowa, and it’s a great way to learn or improve your gonioscopy skills. And then lastly, intraoperative practice. You’ll see that hand positioning and stability are very different in phaco, which is shown on the right, versus gonioscopy or MIGS, which is shown on the left. Your elbows are gonna be more extended than they usually are, and you’ll be likely sitting a little further away from the patient than usual. You will be working under bimanual conditions, by obligation, with the gonio in your non-dominant hand. I recommend before you start gonioscopy — before you start a MIGS surgery — that you do intraoperative gonioscopy multiple times. You can do this before or after phaco, or any other sort of eye surgery. Just go ahead and try to visualize the angle, and you can even take a small hook or a cannula and navigate over to the angle and get used to working within that space. As you might guess, it’s safer to do this after phaco, when the lens is already out and the angle is a little deeper. Anesthesia choice is worth discussing. The vast majority of MIGS can be performed topically. Resulting in faster patient recovery. So it’s very nice to be able to do that. However, keep in mind a retrobulbar block is good for beginners. You can ensure that the eye is gonna be more stable. And I also think it’s nice for 360-degree cannulation procedures, which can sometimes be a little more uncomfortable for the patient than your focal nasal work. It is possible, though, with a retrobulbar block, for the eye to rest exotropic a little bit, and we’ll get into that later why that can be troublesome. Wound construction is just as important in MIGS as in any other procedure. It is your access to the eye, and to the angle. And it can really impact your view, your mobility, and your ergonomics. So before you make any incision, you must know the anatomy of your intended gonio lens. There are all kinds of different direct gonio lenses, with different sorts of fixation rings, contact shapes, et cetera, and this might impact where you place your wound. So you want to be cognizant, so you can avoid bumping into your lens with the instrument. Make sure your incision is pointed towards the targeted angle, especially a paracentesis. It’s not always gonna be radial. Sometimes you’re gonna want to point it right towards the nasal angle. And for most procedures, you want to center your main wound temporally, to target your angle. This will maximize your range of movement. Here if this is a temporal incision, you’re only gonna want to work so much within the incision. So you want it to be centered on the area you intend to work in. You also want to take care to avoid limbal vessels. If you’re too posterior, you will run into bleeding that will cause trouble throughout the case, and we’ll touch more on that in a little bit. I think it’s best to go for the smallest workable incision that you can. That way, you have less loss of OVD. But an incision that’s too small makes it hard to get in and out, and you can get locked in the wound. So finding the right balance is important. Once you know your lens, and you have your wounds, you must move the patient and microscope to get a view. The way you do that is you’re gonna rotate the microscope about 35 to 40 degrees towards the surgeon. This can be done by the circulator. The circulator can also tilt the oculars up for you, as you’ll see, as necessary in this picture. While this is happening, you want to turn the patient’s head away from you, 35 to 40 degrees, and you’re gonna ask the patient to look straight ahead. Again, I urge you not to be shy about turning the patient’s head away from you. This is crucial. The ultimate goal of this repositioning is to get coaxial light entering parallel to the iris. Pointing into the angle. This will help you best achieve an en face view. So as soon as you put the lens down, you’re gonna have to be looking for landmarks. And there are a few helpful ways to quickly identify the trabecular meshwork. You can look for pigmentation. A lot of elderly patients have nice pigmentation. And you’re also gonna be targeting areas of pigment in some procedures, so this is a nice landmark to look for. Some patients will have blood visible in Schlemm’s canal. And this typically occurs when pressure is on the lower side. Another really nice way to visualize TM is Trypan blue. This was described in JCRS by Parker et al. in 2017. And all you have to do is inject Trypan, and leave it in for about 30 seconds. You rinse it out and proceed as usual, and you get a nice blue staining of trabecular meshwork. That way you’ll have no question as to where you’re working. Awareness of landmarks is crucial not only for success, but also for avoiding complications. Just to remind you of the area you are working in. We all know that it’s 3 millimeters, but the length of the TM is anywhere from 575 to 800 microns. And the AOD is on average, in a normal eye, around 300 microns. And it gets even smaller and narrow angles. Nearby vulnerable structures include the iris and ciliary body. This picture shows a small iridodialysis, next to an iStent, and we’ve seen multiple cyclodialysis clefts referred in after gonio surgery. Descemet’s membrane can easily be nicked. Posterior wall of Schlemm’s canal, which is less crucial, but it can still be damaged, and then of course lens and zonules are there, if you’re working in a phakic eye. So once you’re getting started, you’ll inevitably encounter issues. It’s part of learning. But the ability to troubleshoot will save you. If you don’t have a skilled teacher at your side, it can be very hard to identify in realtime exactly what you’re doing wrong. Corneal folds are a common factor that will impair your view. They occur in three situations. Either the IOP is too low, and in this situation, you can add OVD, cohesive OVD is nice. It creates space. But it does burp easily. So you’ll want to check your wounds. And a dispersive OVD plug can be used at the wound to hold in your cohesive OVD. Your gonio pressure may be too high. It’s easy to do this in the beginning, because it’s hard to think about both hands at the same time, and you’re trying to manipulate the eye to get it to do what you want. But go ahead and check your positioning, and try and lighten your touch. And third, you can also have tension on the wound. When you’re working in a wound, if you’re putting tension on it, you’re gonna create corneal folds. So try to relax your tension and reposition. I have a nice video to illustrate this point. You’ll see I have a beautifully clear view, here, in the beginning, with nice pigmented TM. I’m going in with an iStent here. This is early, early, probably even in residency. And engaging trabecular meshwork. And I’m laterally translating in the wound, until I run into the wound edge, and then you’ll see I have a bunch of corneal striae in my way, because there I am at the edge of my wound. To avoid this, I should treat the wound as a fulcrum, rotating the base of the instrument right, as I work to the left. Another very common problem is a top-down view or under-rotation. You may notice when this happens that you feel like you can’t quite see into the angle. It’s as though the posterior cornea is blocking your view. And the risk of operating under this condition is misjudgment of angle anatomy, Descemet’s injury, because you’re right there by cornea, or difficulty with stent placement, which is crucial. You have to have an en face view for stent placement. Solutions for this are to rotate the head further away from you, or rotate the scope more towards you. In a pinch, you can have the patient look away, and we’ll talk a little bit more about this. I have a video showing how easy it is to under-rotate here. The gonio lens is going on. Everything is looking good. And it almost looks as if this patient has an entirely non-pigmented angle. But fortunately we’re able to recognize a problem. We know there’s pigment there, from our in-clinic assessment. And so we move the scope more towards the surgeon. And then also rotate the head a little further away. And you can see now our view is dramatically better, and there’s actually quite a lot of pigment in this patient’s trabecular meshwork. This is early on, so I’m going in with a Sinskey hook, to just kind of navigate the angle a little bit, and get used to working in that space. Like I mentioned earlier, in a pinch, you can ask the patient to look away for you. But I will caution you in doing this, as it’s very hard for patients to maintain this position of gaze, especially if they’re mildly sedated for surgery. They tend to get endpoint nystagmus, which is no doubt suboptimal for gonio surgery. So you can see that fine nystagmus here, as that patient is trying their best to help you out. One of the most frustrating issues with gonio surgery is blood. You can have blood on the front of the lens or dried OVD or even water. Any of those things can degrade your view. The front of the lens must be dry. You can also get blood between the cornea and the lens. This is frustrating, because it’s usually from limbal bleeding. But you really just have to rinse, and you can try to tamponade the area of bleeding. And you rinse and add more OVD to continue to maintain your view. And you can of course get blood in the anterior chamber. Blood in the AC is actually nearly unavoidable. In fact, reflux with gonio surgery in MIGS is normal. A well targeted goniotomy or stent, if connected to the venous system, like it should be, will bleed. But as we all know, time in the angle is your view. So the longer you’re there, the more rapidly your view is gonna decline. So in order to minimize bleeding, I would encourage you to act with intention. Partially incising TM and then backing out, or hesitating, or bumping around in the angle is not what you want to do. If you do encounter blood, though, you can add OVD, which usually clears the view, and helps tamponade things a little bit. But you can move the blood out of your way. I encourage you to move it to the side and not mid-AC, because it’s still gonna be blocking your view. If all of this is still failing, you can wash out and replace the OVD, but fortunately this is rarely necessary. I’ve got a video to illustrate all the fun you can have with blood. And how important it is to manage heme. So you’ll see it looks like a good incision. But pretty rapidly, you can tell we’re a little too posterior. Now blood is seeping onto the cornea, and mixing in the OVD that we’ve put on the eye to couple. The view initially is okay. The surgeon is using the Kahook dual blade here to do a goniotomy. But pretty quickly you’re getting blood under the lens, between the lens and the cornea. We’re doing the rinse and repeat option. But again, rapidly accumulates. And now there’s blood on the back of the lens as well. So you’ve got to rinse the cornea, but you also have to rinse the back of the lens. And once we do that, the view is once again good. But probably not long. So if your view is still blurry, after all of this, it could be that you’re too zoomed out. Gonio surgery takes a fair amount of zoom. So try to get zoomed in enough that you’re in the angle and really can see things well. I found that gonio surgery really triggers my accommodation, as a young surgeon. It’s a lot of zooming in and zooming out and focusing up and down. So you can get in an accommodative spasm. If you feel like you can’t see no matter what you’re doing, take a moment and look away from the microscope. Patients with a lot of conjunctival chalasis will give you trouble, because the chalasis will come up onto the cornea and can get in the way and block your view. As eye surgeons, we all know that bubbles are the enemy. And also corneal edema can really cause trouble, when you’re trying to do angle surgery. This brings me to the next point, in a question of when to do MIGS. Should you do it before or after phaco, when you’re pairing the two? I think doing it before, when the cornea is clear, the patient’s less wiggly, and you have a physiologic globe, with the lens still in place — those are all beneficial things. But the downsides of doing it before is you can hit the lens and you might have a phacomorphic view. The opposite is true for doing surgery after. And I think if you’re new to angle surgery, it’s best to do this after the phaco, because the angle is more open, and it’s just a little bit safer. All right. We’re quickly gonna switch gears, to review indirect gonioscopy. Indirect lenses are mirrors or prisms, used to reflect light from the angle, so that it leaves the eye perpendicular to the face of the contact lens and towards the examiner. This is what you’re used to from clinic. This is an Ahmed gonio lens. We use this a lot here at Kellogg. And it’s a really helpful indirect lens, as it has a handle that conveniently rotates 360 degrees around the lens, so you can hold the handle still, while twisting the lens, or you can move the handle while you’re holding the lens still, and switch hands that way. But non-handled lenses work just as well. Major differences between indirect and direct gonioscopy — again, there’s no need to rotate the head, which is really nice, and you can work in primary while viewing the angle. So you can quickly pop the lens off and on and get a good view. You are, however, working with mirrors, so it takes a little time to get used to that reverse action. And then common uses for indirect gonioscopy we use here for ab interno Xen implantation, goniosynechialysis, cleft repair, and a general view of superior, inferior, and temporal angle. Maybe you’re doing phaco, and you want to see if there’s a residual lens fragment or something like that. Indirect gonioscopy can be really quick and easy for that. When you are using the indirect lens, make sure your focus, centration, and light are over the mirrored part, not the contact part. Or else things won’t seem like they’re in focus. Here you can easily see the superior angle with the Xen that has been implanted. The head of the patient is straight on in this situation, and the eye is in primary, and we could easily twist the gonio lens 360 degrees to look at the angle. This is a video of goniosynechialysis. Again, we’re looking at the superior angle, and you can see the PAS right here. There are lots of ways to lyse synechiae. You can use microforceps or a cannula. But here, because this is after phaco, and we’ve already got it open, we’re using the I/A, and you can just tip down gently, aspirate a little portion of the iris — you want to be gentle, again, with this, so as not to induce too much inflammation, but you can just aspirate the iris a little bit, and gently pull free those synechiae. You can see there those peripheral anterior synechiae are lysed now. For part two, we’ll talk about tips on individual MIGS. But I do want to start again with the poll question. So what is your current level of experience with MIGS this time? Not so much gonioscopy, but MIGS. Do you have no experience, a few cases, are you proficient, but you could improve, or are you skilled and could teach? Okay. So the vast majority of you have no experience. So I want to start pretty basic. I think this is really helpful. The AGS, American Glaucoma Society, and the US FDA came together to set up a definition for MIGS, and determined that all MIGS should do the following: They should lower IOP via an outflow mechanism, they should be done either ab interno or ab externo. They should have limited or no scleral dissection, and minimal or no conjunctival manipulation. So just to check your understanding of MIGS in general, which MIGS, if you had to categorize them, have an IOP safety net due to episcleral venous pressure, and are therefore less likely to cause hypotony? Trabecular bypass surgeries, suprachoroidal shunts, subconjunctival shunts, all of the above, or none of the above? Good. So about half of you got it right. It’s the trabecular bypass-type surgeries. About 30% answered subconjunctival shunts, so we’ll chat a little bit about that. So the same AGS-FDA working group also categorized MIGS by the recipient outflow reservoir, which has a significant influence on both safety and efficacy for MIGS. They categorize them as Schlemm’s canal — these are the ones that have a lower risk of hypotony. This is because they still rely on the physiologic outflow system. Along those same lines, they have efficacy limitations. Their success does depend on patency of the distal outflow system. And for the same reason, as we’ve already discussed, they have an increased safety profile. So they have less hypotony, due to limitation of low pressure by episcleral venous pressure. Suprachoroidal and subconjunctival MIGS are non-physiologic and theoretically more efficacious for this reason, but this comes with increased risk of hypotony, and the possibility of disuse atrophy of the physiologic outflow system. Subconjunctival procedures also carry the risk of infection, because they do form a filtering bleb. Currently, in the US, we have no access to suprachoroidal shunts, so I won’t be able to comment on this today. I have no experience using these. And because of variability in global access to subconjunctival stents, and for the sake of time, I won’t be able to dive into subconjunctival stents, but I’ll say I’m very impressed by Xen, and excited by preliminary results for InnFocus, and there’s a lot online about these procedures that you can access. I will spend the rest of the talk diving into Schlemm’s canal type procedures. Especially my personal favorites, goniotomy and trabeculotomy. I think these procedures are perfect for a global webinar, as they require nothing more than tools typically found in the OR. Stents, again, may or may not be available where you are, but given their popularity as quote-unquote “starter MIGS”, and their excellent safety profile, I will give a few tips on these surgeries. There are innumerable videos on how you can do each step for each procedure, so I will try to stick mostly to just tips that you might not find elsewhere online. Once you’ve cleared the patient for direct gonio, patient selection is crucial for deciding which MIGS procedure you will do. Schlemm’s canal stents are most appropriate for mild to moderate glaucoma. These patients should have an IOP target of mid to high teens. In the vast majority of studies, including the COMPARE trial, which looked at iStent versus Hydrus as a standalone procedure, patients ended up with 17 millimeters of mercury on average. They required fewer meds, which is a huge benefit especially if there are access to medication issues or compliance issues, and in general, patients are okay to stay on their blood thinners. But if they are on a prophylactic aspirin, I would recommend that they stop it, just because I’ve seen a few hyphemas after stents. On the right, you’ll see the first generation iStent on the top. The body of the stent is placed in Schlemm’s canal, and the snorkel is what is accessing the AC. The Inject is in the middle. This is a second generation Glaukos product, and these are small dart-like stents injected into the TM in two locations, and on the bottom is the Hydrus stent, which is put into Schlemm’s canal, and it has one inlet here, and causes dilation along its length. I have a video that just shows a routine first generation iStent. This is courtesy of Manjool Shah, one of my mentors. He’s using a tip-up configuration, and then flattening out to stay in Schlemm’s canal. This is an iStent to the left. And then slowly releasing. And kind of tapping the stent into place. And then fast-forward. We’re gonna go to the other side, the iStent to the right. Same approach. And leveling out once in canal, and you’ll see reflux heme. It’s important to approach the trabecular meshwork at about a 30-degree angle, so you properly engage canal, and avoid superficial implantation. With iStent Inject, there is a trocar that is placed into the trabecular meshwork. And the tube of the inserter is used to dimple down into TM, and once this is done, you click the button, and it inserts a stent into TM. And then it’s preloaded with two stents, and you get four clicks. The same process. You’re threading the trocar through TM, dimpling in with the injector, and then injecting the stents. It’s crucial to have an en face and zoomed in view, so you can see how the trocar is lined up. Additional tips. I’ve already mentioned the importance of an en face angle view. You should try to target areas of pigment or heme reflux. And also for iStent, I feel like it’s really crucial to be decisive and not to linger in the angle. Again, the angle of approach is critical, and it’s a little different for each type of stent. If you’re noticing resistance during implantation, you should stop and troubleshoot. You may be running into the posterior aspect of Schlemm’s canal. Or a stricture. Or you may be actually just running into your wound, like we’ve discussed before. And the other important thing to remember is: Viscoelastic is a device. So if your stent becomes dislodged, you can use OVD to kind of suspend the stent for reloading, and I’ll show you a video of that in just a little bit. Here’s an example of what happens when you have a top-down view, or under-rotation, when you’re trying to implant a stent. I have no en face view here. You can see the stent disappears under the cornea, as I go out into the angle. And obviously implantation was unsuccessful here. But recognizing the issue could have made this procedure much easier. In this video, the Inject has come off the guide wire, and needs reloading. The surgeon can’t quite get the Inject back onto the trocar, without some assistance from OVD. So what you do is use some cohesive OVD to float that stent right into the position you want it to be. So that you’re looking straight down the lumen. And then you can easily thread the trocar back through the stent, and you’ll be able to inject it. I don’t have great videos of Hydrus yet, because I’m still working on learning this one. But so far what we’ve learned that is not anywhere in the manual, or that I’ve seen online, is that Hydrus is really finicky, when it comes to angle of approach. So as you’ll see in the graphic, this is from the FDA manual — the Hydrus really needs to be flat against TM. You don’t want that 30-degree approach you use for iStent. It has to be flat and really close and snuggled up to trabecular meshwork. Because as you deploy it, you want the stent to follow the curve of the canal. If the angle of approach is too large, it will pop out the other side of the canal, as you see here. Hydrus is nitinol. It has shape memory. So you really want it to be lined up, so it stays within-canal for three clock hours. Otherwise you lose about a clock-hour of effect. So patient selection for goniotomy/trabeculotomy is similar, but there are a few key differences. Again, this is a similar population of mild to moderate glaucoma. But the IOP target might be slightly lower, or the medication or disease burden slightly higher. That’s sort of how I pick these patients. Blood thinners are an absolute contraindication for 360 procedures. But a relative contraindication in goniotomy. These TM excising procedures work really well in steroid-induced high pressure, as they address the area we think is most affected by steroid-induced glaucoma, the trabecular meshwork. Similarly, they can be done in uveitics, because these procedures aren’t that inflammatory. So a controlled uveitic, they often have an overlying steroid issue as well, so they do really well for goniotomy-trabeculotomy-type procedures. I will caution you, for patients who are status post vitrectomy, they can get overwhelmed by heme and it can cause prolonged visual recovery. Here you see a nice goniotomy cleft, and this is a Kahook dual blade. General basics for goniotomy is you’re gonna create a temporal wound with a nasal target. It’s direct gonio, in an ab interno approach. You’re making a nasal incision of the trabecular meshwork with a blade or a needle. And you’re aiming to carve out about three clock hours of trabecular meshwork. I have a video of a basic routine Kahook. Again, this can be the Kahook dual blade or a needle. We’ll talk about that a little bit more. But you can see the dual blade action that’s meant to carve out a trabecular strip. And once you’re in Schlemm’s canal, the goniotomy blade tends to want to stay in the canal. Which is helpful. Sometimes you’ll meet a little resistance, and then break through a stricture, as the surgeon just did there. And as far as tips go, again, you don’t have to have a Kahook dual blade. You can use a bent 25-gauge needle. This has been described. You can also use the heel of your goniotomy blade to lyse peripheral anterior synechiae, while you’re in there, and when you’re working in extremes of view, you feel like your lens is running out of view, I would urge you to err with your tip a little bit. So if you hit a structure, it’s peripheral Descemet’s, and not iris root or ciliary body. And if you’re feeling greedy or lucky, you can bend the needle to increase your degrees of goniotomy. This is a 25-gauge needle. And a hemostat is being used, a large bulky hemostat is being used, to bend the tip of the 25-gauge needle. And when it’s all said and done, this simulates the action of the Kahook dual blade. You have two cutting surfaces and a scooping action, but this is sharper than the Kahook dual blade, so be very careful when you’re using this technique. In this video, you’ll see where you’re using the heel of the Kahook dual blade to lyse PAS. Also notice the surgeon widening the inner ostium of the wound. This can help with range of motion. And you see right there, just gently using the heel to break some low PAS, and scleral spur is much more visible. And so basics for your 360-degree procedures: Similar, but different. You’re gonna have a temporal incision with a superior-temporal and anterior-temporal paracentesis. Again, it’s direct gonio, from an ab interno approach. And if you’re going to use a suture, you’re gonna melt the tip of a 5-0 prolene with a hot temp cautery, or you could use a 4-0 nylon. This has also been described. The purpose of the bulb is: As you thread the suture, it won’t back out on you. It sort of acts as a barb. And if you cannot cannulate for a full 360 degrees, you can pull the suture and do a partial goniotomy. I recommend you make a small nasal goniotomy to start. Then you’re gonna cannulate or thread Schlemm’s canal for 360 degrees. And then rupture trabecular meshwork for 360 degrees. And you end up doing an OVD-BSS exchange. You do this multiple times to prime the system and really push fluid out through the distal collector channels. On the left, you’ll see a pretty zoomed in view of a 5-0 prolene that has been melted. Getting the bulb the right size is crucial, and this is a good example. You don’t want it to be too large, because you’ll have a hard time threading the goniotomy, but you also don’t want it to be too small, because then it loses its purpose. On the right, you’ll see that the curve of the suture is lined up perfectly to follow curve of canal, so you’re gonna be threading to the left here. But make sure this is lined up, and make sure you have plenty of slack. This is a graphic taken from the original descriptive paper by Grover et al.. And again, you’re just gonna start by cannulating or threading the small goniotomy here. You’re gonna thread for 360 degrees with this microforceps, until the other end of the suture emerges. You’ll grab the distal end of the suture, and you’ll also grab with a forceps, outside of the eye, and you’ll pull both ends of the sutures to cause 360-degree rupture of trabecular meshwork. Tips: Make sure your para is pointing to the work zone. Again, you want a small nasal… Let me back up. You want a small nasal goniotomy. It makes it easier to thread. And be sure you have slack before threading. This is an ideal size of a goniotomy. It’s small, no wider than a 25-gauge needle or an MVR blade. That way your tip is not popping out, as you’re trying to thread the suture. And then as far as grab tips, it’s really important to pick up the prolene 2 millimeters behind the bulb, with the very tip of your microforceps. Mind Descemet’s membrane while threading. And if you meet resistance, back up and try again. You can also pull it out, and go the other way. Again, don’t force it. You could be going into the suprachoroidal space. Here’s a video that shows some grab tips. Here the surgeon grabs a little too far back. So they’re correcting their grab. Sorry, the view is poor in this video. But they’re trying to grab — and the actual forceps are bumping into the back of the wall of Schlemm’s canal. So it’s impeding them from threading the suture. There they’re grabbing too far away, so they don’t have the right vector forces. And then here, finally, regrabbing in a proper location, and they’re able to thread. In this video, the suture has popped out somewhere along the way, so we’re grabbing each end, and doing a partial goniotomy. And then we’re gonna line the suture up correctly. And start threading the other direction. First of all, I’m not grabbing right at the tip, so I’m bumping into the back of Schlemm’s canal there. But finally able to cannulate and thread the suture. Again, when it comes around, you’ll grab the other end, and you’ll complete another partial goniotomy, to hopefully get that full 360 trabeculotomy. Postoperatively, a few tips. In the OR, as soon as you’re done, as soon as you can get the drape up, I would encourage you to sit the patient up. This allows any blood to settle out of the patient’s view. You can leave some OVD in the eye, if you’re worried about bleeding. It will keep the pressure a little higher and tamponade bleeding. I use steroid and antibiotic as usual. And postoperative bleeding — if you notice PAS, blood in the cleft, or hyphema, you can add pilocarpine, that can potentially help with scar tissue formation. And I would urge you to be cautious with postop IOP drops. Because if IOP is too low, you’re gonna get backbleeding, but also if IOP is too high, you don’t want to cause further optic nerve damage. These are my references. And I’d like to thank several folks that helped me with either gonioscopy or learning MIGS surgery along the way. And also Hunter, for always encouraging me to do these webinars. I can take questions.

DR PROVENCHER: So one interesting question that came in is: The role of binocular vision during this technique. I think binocular vision and stereopsis is crucial for MIGS surgery. I would be curious to know if this surgeon does cataract surgery under monocular conditions. I could imagine it would still be possible, based on other cues, but I think it would be much more difficult, when you’re navigating such a small space, to be safe. Another question is: Do you use MIGS for advanced glaucoma? There are a lot of studies out right now on this. And they can be used for refractory glaucomas, but I think in general, we here use them for mild to moderate disease. Patients that desire to be off a drop or two. And we typically reserve advanced glaucoma for more traditional procedures, or even your bleb forming procedures. Another question: What is the biggest problem/difficulty when you start MIGS? I touched on this a little bit, but really for me, it’s getting and maintaining a view with gonioscopy. It’s so easy when you’re starting out to be focusing on your dominant hand MIGS device. When the other hand is pushing on the cornea, causing folds, or you’re losing viscoelastic through your wound. So really practicing intraoperative gonioscopy and being cognizant of your non-dominant hand, and what the gonio lens is doing, is really important. So I think that’s the biggest struggle, when it comes to learning MIGS. We see as a tertiary referral center, at Kellogg, we see a lot of complications come through from MIGS surgeries. So even though they’re advertised as very safe, and they can be very safe in skilled hands, they’re not completely benign, so you’ve got to be really careful when you’re working in the angle. There are a lot of structures that can be damaged. And then there was a question. The glaucomatous patient can get a relief after MIGS procedure? If yes, how? I think that’s a really good question. Because there are a lot of ways MIGS can impact the person’s lifestyle. The recovery time after MIGS, compared to traditional surgeries, and the low, low risk of infection that you would assume by going into the eye, those are very different, compared to traditional surgeries. A lot of our patients note the improvement in quality of life, and the way their ocular surface feels, when they can get off just one or two drops from MIGS surgery, so even if their absolute pressure doesn’t change a whole lot, but they’re able to stop a medication, that can make a really big impact on their life, and also costs are an issue, or access to medications are an issue. MIGS procedures can work really well. There’s a question. Can the Xen gel stent be done ab externo? Yes, there’s a lot of buzz about this right now, through the American Glaucoma Society email network. I haven’t myself done it. I really like the ab interno approach, and I’m comfortable with the ab interno approach, but there are a lot of videos on the ab externo approach, and the main benefit and thought behind this is making sure that the subconjunctival tip of the stent is in the correct location.

DR PROVENCHER: Okay. So in which cases do you still prefer trabeculectomy? This is an awesome question, because trabeculectomy is still alive and well. I think in your patients that really truly need a low pressure, pressure under 12, under 10, there is no MIGS procedure at this time that I’ve been able to use, that achieves those low pressure targets. So even in your comparative trials of Xen versus trab, which — the outcomes were similar — you still really, if you need a patient as low as under 10, you can only get there with trabeculectomy. Oh, yes, the question again on the suture material for GATT, or the 360-degree trabeculotomy, we use 5-0 prolene. But there are also reports of using 4-0 nylon. So either of those sutures. What is the difference between minimally invasive glaucoma surgeries and microinvasive glaucoma surgeries? I don’t think there’s any difference. I think it’s just semantic, and the way different people say it. But technically, the term here is minimally invasive. How do we manage hypotony after MIGS surgery? Typically hypotony after MIGS surgery is rare. Especially in your canal-based procedures. So the ones that follow your physiologic outflow. Hypotony is very rare. And usually self limited. A lot of times these patients were on a ton of meds, before they went into surgery, so once those meds wash out, pressure picks up, and even if they were hypotonous, it’s usually of little consequence. They might get a little more bleeding than usual. In the filtering surgeries, like the Xen, that I have experience with, they often are hypotonous early, but it’s not a clinically significant hypotony, like you get with trabeculectomy. So I think it’s the more controlled outflow that you get through the Xen stent. But even if they have a pressure of 5 or 6, if the chamber is still deep and they don’t have choroidals or hypotony maculopathy. Any special instruments for MIGS, especially in low resource settings? That’s the primary reason I focused on goniotomy and trabeculotomy. Those can be done with a bent needle, or a melted tip prolene or nylon. For GATT, you do need microforceps, so you’ll need some sort of forceps that can access the nasal angle from the temporal approach. That’s the only special instrument you really need. There’s a lot of description of using a lighted microcatheter for GATT, but you really don’t have to have that. I actually prefer the 5-0 prolene. Can MIGS be used in glaucoma postop vitreoretinal surgery? Yes, I did mention that I would caution you in doing this. In the postvitrectomy eye, globe compliance is a little more, and if you get hyphema after or during surgery, it can spill over into the vitreous cavity, and you can have prolonged visual recovery, so that is the risk and the downside. So in general, I try to avoid trabeculotomy, goniotomy, in these patients, but a stenting procedure would be, I think, fine. Is Express shunt a MIGS? Good question. I think it falls outside the category of MIGS. At least the classification established by the AGS and FDA, because there is conj dissection, and there is a scleral flap that is created. You should not be doing scleral flap dissection or major conjunctival manipulation. So this is a question… It sounds like it’s an individual patient. Would you use MIGS for ocular hypertension with a cup to disc ratio of 0.4 in the right and 0.1 in the left with average IOP of 32 in a patient not using drops reliably? Without seeing more data, I would say it sounds like going into this case that you could use MIGS for this patient. It doesn’t sound like they have much disease burden. Although we’d need to see a field. And know more about them, but I think this could be an appropriate patient for MIGS. Can we use Kahook in pediatric glaucoma? I don’t have much experience with pediatric glaucoma, though we know goniotomy is the primary procedure for primary congenital glaucoma. So I don’t see why a Kahook dual blade couldn’t be used, as opposed to a needle. But I can’t comment on that for sure, because I don’t do pediatric glaucoma. And then what about long-term output with MIGS? I don’t know if you can clarify your question. I don’t know if you mean long-term outcomes. I think the data we have so far goes out to two years, in most cases, and the data is decent. It reflects what early outcomes are.

DR PROVENCHER: How steep is the learning curve for MIGS? I think it’s pretty steep. I think once you get a handle on gonioscopy, you can really learn MIGS quickly. Especially the MIGS that stand out to me that are easy to learn is a nasal goniotomy, like a Kahook dual blade. That’s something I felt very comfortable with quickly. Your iStent placement is a pretty quick learning curve. And then even 360-degree trabeculotomy procedures. It’s really maintaining the view, once you get good at that. I think the learning curve is steep. So I would encourage you to consider this for your patients. Then we had one more question. What is the incidence of cystoid macular edema with MIGS? I don’t have a number for this off the top of my head. So often it’s paired with cataract surgery, so I would say it’s similar to post-phaco CME. I have only seen one case of cystoid macular edema after a Xen, and most of these procedures, like I said, are minimally inflammatory. So I would hypothesize that the macular edema is coming more from the phaco than from anything else. Of course, if you’re hitting iris, that’s a different story. Because you’re releasing a lot of inflammatory mediators that way. But a well performed MIGS procedure, I would say cystoid macular edema overall is very rare.

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June 1, 2019

Last Updated: October 31, 2022

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