Lecture: Maximally Effective Minimally Invasive Glaucoma Surgery

This lecture will provide learners with knowledge of minimally invasive glaucoma surgeries (MIGS), as well as how to make the best choice of procedure for any given patient. Some MIGS are for people with early glaucoma, others for patients with late stage disease. At the conclusion of this talk, learners will be able to select the correct procedure for the correct person.

Lecturer: Joel S. Schuman, MD, FACS, Director, NYU Langone Eye Center, New York, USA


DR SCHUMAN: Hello. I’m Joel Schuman, and it’s a pleasure to be with you on Cybersight this morning or this afternoon or this evening, whenever it is for you wherever you are. I’m going to discuss maximally effective minimally invasive glaucoma surgery. I’m the director of the Langone Eye Center at New York University, and I’m happy to be spending this morning with you. First question: What is your level of training? Please reply on the poll. We should have the answer in just a moment. From the group. And half of the group are ophthalmologists and 15% are glaucoma surgeons. We have some residents and some medical students. We have a good group here this morning. So let’s talk about microinvasive glaucoma surgery. So what is or are MIGS? Glaucoma surgery with a lower risk than trabeculectomy or tube implant. They often avoid disruption or even entry into the conjunctiva. There are some exceptions. Canaloplasty and InnFocus MicroShunt are exceptions. Most are designed to restore function to the conventional outflow system, with the exceptions of the Gold Shunt and the CyPass in addition to the ones I mentioned. So what’s the big deal with MIGS? In general, with MIGS, you can achieve a mid to high teens intraocular pressure, on average. There are always gonna be those patients where you have a better result, a lower intraocular pressure, or a worse result. But on average, you’re looking at a final intraocular pressure in the mid to high teens. So you have to consider whether or not the patient that you’re operating on will be safe at that sort of intraocular pressure. Your choices include ab interno trabeculectomy, a trabecular bypass shunt, Schlemm canal implants, tube shunt, or an anterior chamber to supraciliary space bypass, or endoscopic laser cyclophotocoagulation. Let’s talk about Schlemm canal surgery first. So a polling question. Please answer yes or no. I have performed MIGS Schlemm canal surgery. And the answers should be coming up in just a second. And this includes all sorts of Schlemm canal surgery, whether it’s removing the trabecular meshwork or bypassing it. So almost 90% of the group has not performed Schlemm canal surgery. So we’ll talk about the options that are available to you and your patients. The mechanism of action is to increase aqueous outflow through the conventional pathway, typically through the implantation of a drainage device or removal of tissue. And here is a list of the procedures or implants that can be used for Schlemm canal surgery. And we’ll start off with the iStent. So the iStent is a titanium device that bypasses the trabecular meshwork and the inner wall of Schlemm’s canal. And on the right, you can see a US penny, and right above the date, by the tip of the arrow, you see the implant. It’s the smallest implant that’s placed in the human body. And these can become obstructed and opened with a YAG laser, and they are straightforward to put in, but not necessarily easy to put in, unless you have facility in operating in the angle, and specifically in Schlemm’s canal. So these are some images of the device on the right. And on the left, you see one such implant in a cadaver eye. And this is from work done by Doug Johnson at Mayo Clinic, where he looked at the effect of the iStent on outflow facility. This is the operation itself. So there is an entry made into the cornea, using a keratome. And viscoelastic is placed in the eye. And then the iStent is placed across the anterior chamber, and into Schlemm’s canal, through the trabecular meshwork and inner wall, as you see here. And the iStent is now in place. It’s tapped back and forth. So in Doug Johnson’s studies, one iStent doubled the outflow facility in perfused human donor eyes, and the insertion of two stents quadrupled it. That was very encouraging. However, the randomized controlled clinical trials did not show the degree of pressure lowering that one might expect from that sort of effect on outflow facility. And the bottom line in these studies was that the reduction in intraocular pressure was similar in patients who had phacoemulsification alone, compared to those patients who had phacoemulsification plus iStent. On the other hand, the patients to have phaco plus iStent required fewer medications to control their intraocular pressure, at the conclusion of the surgery. After 24 months, the pressure decrease was 8% in the phaco plus iStent group, versus 1% in the phaco group. In a five-year study of 13 combined phaco and iStent procedures, there was a 16% reduction in intraocular pressure from a baseline of 19, and 42% of those patients required no additional medication. And in a standalone iStent implant study, 27% intraocular pressure decrease was seen after a year, with a mean reduction of medicines from about 3 to 2. And then there was a retrospective analysis of standalone stent implantation on pseudophakic patients that showed good pressure lowering at 2 years, from about 20 to about 13 or 14. And then in a prospective series of patients with moderate to severe glaucoma, 40% of whom had previous glaucoma surgery, at 36 months there was a 36% average reduction of pressure from baseline, and an 86% reduction in the number of medications. In a study that compared two with three iStents, combined with phacoemulsification, there was a 30% pressure reduction in both groups after a year, and 46% of the patients with two stents were off of medications at one year, versus 72% of those with three iStents. In a study that compared one versus two versus three iStents, 90% of patients with one stent, 90% with two stents, and 92% with three stents achieved a pressure reduction of at least 20%, with an absolute value of 18 millimeters of mercury or less, and with each stent there was a significant reduction in pressure. The iStent has been improved to a new device called the iStent Inject. So placing the original iStent required entering Schlemm’s canal and the inner wall, passing through trabecular meshwork and the inner wall, and the newer device just requires you to inject what looks like a rivet into Schlemm’s canal, through the trabecular meshwork and inner wall. So it’s a little bit easier to place, in some ways. It’s a single piece device. You can see it on your right hand side here. And it’s been approved in Europe and in the US, and other parts of the world. In prospective studies, the iStent Inject has similar efficacy to the iStent, as we talked about just before. And in a study with POAG and pseudoexfoliation glaucoma patients, pressure decreased by 33% and 35%, respectively, at six months postoperatively, following placement of two stents. And in both groups, there was a significant reduction in the number of medications required. In comparison with cataract extraction plus trabectome by phacoemulsification, versus trabectome alone, versus the phaco plus two iStents in the contralateral eye, the safety profiles of phaco plus trabectome versus phaco plus two iStents was similar. And this is the Pivotal trial in the US for phaco plus two iStents versus phaco alone. And you can see that the phaco plus two iStent group did considerably better at 24 months than the phaco alone group. And there were similar safety profiles in the two groups. And then this study looked at the outcomes of patients for 36 months, after iStent Inject implantation. And again, you can see pressure lowering into the mid teens. On average here, at 36 months. Notice that the n here, the number of patients reaching this endpoint, is half of those who started in the study. So you need to be a little bit careful in interpreting that. And this is the percentage of eyes with a pressure of 18 or less, or 100% at 36 months, and only 27% at pre-op. And at a year, it was 97%, then 96%. So again, good efficacy with two iStent Inject implanted. The next Schlemm canal device is the Hydrus. This again is a trabecular meshwork and inner wall of Schlemm canal bypass device. It sits in Schlemm canal. It’s quite a bit larger than the iStent, and it dilates up to three clock hours of the trabecular meshwork. And you see the device here. And here it is in place. And you can see that the trabecular meshwork and inner wall of Schlemm canal are overlying the device, and then you see the exposed tail of the device here, with an inflow port. And this is a placement of the device, and this is IK Ahmed, doing the procedure. And I’m going to just speed through, so that you can see the implantation. And here the inserter is being placed into the trabecular meshwork, and then Schlemm canal, and then the device is going to be inserted. And here you see the device going in. And then it’s released from the inserter, and here is the device in place. In human cadaver eyes, this device was studied by Haiyan Gong. We have good experimental data on this, looking at outflow facility. There were 14 eyes implanted with a Hydrus Microstent, 7 contralateral eyes served as controls, and there was a significant increase in outflow facility, allowing more flow into Schlemm canal and the episcleral veins, and the implantation did not cause any obvious damage to the outer wall of Schlemm canal, beyond the microstent entry point into the trabecular meshwork. Preliminary data on 28 patients who were implanted showed that combined phacoemulsification and Hydrus insertion resulted in a 15% reduction of pressure from baseline of 18 millimeters of mercury, and medications decreased from 2.5 to 0. In another preliminary study, there was a 35% decrease in pressure from 25 millimeters of mercury at 12 months, and the most common complications of all of these Schlemm canal implantations are transient hyphema, and of peripheral synechiae of 10% in this case. In phase II randomized controlled clinical trial, patients received phacoemulsification plus Hydrus versus phacoemulsification alone and were followed for two years, and at the end of two years, the pressure was significantly lower for the Hydrus group versus the control group, 17 versus 19, and 80% of the Hydrus group had a 20% reduction in washed out diurnal intraocular pressure versus the control group. In a nonrandomized prospective case series following Hydrus implantation, the pressure reduction was not significant between the two groups, but the Hydrus group had significantly greater medication reduction than the SLT group. And in less than 10% of patients there’s a transient early pressure spike from baseline. And here are some data from that study. This is the Horizon study. And this was a randomized controlled clinical trial of phaco alone, versus phaco plus Hydrus in 369 eyes and 187 control eyes. And here you can see the percent of eyes with more than 20% reduction in intraocular pressure, compared to baseline, and the numbers for Hydrus are significantly higher than the numbers for phaco alone. And here you can see the results graphically, in terms of the percent that were unmedicated at each time point. Let’s turn now to trabectome. Now, we’re going from putting devices into Schlemm canal to removing the trabecular meshwork and the inner wall of Schlemm canal. So trabectome is one device for doing that sort of an ab interno trabeculectomy. It ablates the trabecular meshwork and the inner wall of Schlemm canal, and that allows greater outflow facility. It uses a high frequency electrocautery, which is used to ablate the tissue. Most common complication with all these Schlemm canal procedures is hyphema. And here you can see the device. This is the portion that sits in Schlemm canal. This is a schematic, showing trabecular meshwork and Schlemm canal here, and this is the outer wall of Schlemm canal. And this is illustrating that the heat on this side of the probe is not very great. It’s only increasing the temperature by 1.2 degrees Celsius. Whereas on this side, it is extremely hot. It’s a plasma. And you can see the intact trabecular meshwork and inner wall of Schlemm canal here, and then the ablated tissue here. And this is the outer wall of Schlemm canal that you’re looking at, after removal of trabecular meshwork and the inner wall. Here you see the remnants of trabecular meshwork and inner wall on the scanning electron micrograph. And this is the procedure being performed. This is being done by Nils Loewen, who has done as many or more of these procedures as anybody, globally, and in his technique, you can see that the device is sliding easily across the trabecular meshwork and inner wall, ablating that tissue. And he’s very careful not to rub the outer surface of the probe against the outer wall of Schlemm canal, so as not to damage the outer wall or collector channels. The other little trick that Dr. Loewen introduced is widening the keratome entry internally. So you would enter the cornea with the keratome here, and then widen the entry to each side, which improves your access to the trabecular meshwork and Schlemm canal, with the probe. So you can ablate a wider area of the angle. The other little trick when entering with the trabectome is to enter, and moving anteriorly into trabecular meshwork and Schlemm canal initially, and then advance parallel to Schlemm canal, and again, never rub against the outer wall. This is that scanning electron laser photomicrograph. And you can see the smoothness of the outer wall and the intact cell layers, the cell layer of the outer wall and collector channel here. And here. So these collector channel ostia are not damaged when performing trabectome in this way. You don’t want to push outward against the outer wall while you’re doing the ablation. There really are not prospective randomized clinical trials to show you for this type of surgery. But there are case series. And in patients who were followed for a year postoperatively, postoperative medicated pressure of 16 from a baseline of 28 and a decrease in medication usage from 1.2 to 0.3. And subjects with pseudoexfoliation glaucoma had a robust response to trabectome, even better than those with primary open-angle glaucoma. This is from the paper by Don Minckler, George Baerveldt, Marina Ramirez Alfaro, and Brian Francis. And again, you’re achieving mid to high teens final intraocular pressure on average with trabectome. And here are some more studies looking at the same thing, in terms of final intraocular pressure. Mid to high teens, and then a reduction in the number of medications required, and this Kaplan-Meier graph shows failure — pressure greater than 21 and not reduced by 20% below baseline for two consecutive visits. Let’s turn now to the Kahook Dual Blade, which was introduced after trabectome. And the Kahook Dual Blade allows the removal of trabecular meshwork and Schlemm canal, but without cautery. So this is a device that is inserted into Schlemm canal, and then lifts the trabecular meshwork and inner wall so that it’s on stretch, and then two blades on either side of that incline slice through the anterior and posterior portions of the trabecular meshwork, allowing you to remove that tissue without tearing. And this obviously is a much less expensive device. It has a blade here at the tip. And it’s simply this hand instrument. There’s no machine involved. Again, no randomized controlled clinical trials to date. Preclinical studies were done by Dr. Kahook, who actually had invented this device for use in a laboratory, so that he could study trabecular meshwork, and then realized that it might be a useful clinical tool. And in the clinic, it shows good efficacy. Mean pressure reduction of 28% at one year, in combination with phacoemulsification, and 64% of subjects having a reduction of at least one medication. And here you see the intraocular pressure results. Comparing the phaco and Kahook Dual Blade ab interno trabeculectomy or goniotomy and the iStent procedures, and you see a similar outcome for the two. And here you see the proportion of patients with a pressure reduction of 20% or greater, and the Kahook Dual Blade achieved a larger proportion of patients reaching that target than the phaco iStent patients. And again, looking at phaco iStent versus phaco Kahook Dual Blade ab interno trabeculectomy, you have a greater reduction in the number of medications required, and here again is another representation of reduction in medications by at least 1 from baseline. All right. We’re gonna turn now to TRAB 360. So this is using a device, a handheld device, made by Sight Sciences, and it is another way for performing an ab interno trabeculectomy, and it’s designed so that you can access all 360 degrees of Schlemm canal in one clear corneal incision. So unlike the prior procedures, which give you access to between 2 and 6 clock hours, depending on how adept you are, with this device, you open the entire 360 degrees of Schlemm canal to increase outflow facility. Again, no randomized clinical trials to date. Preliminary studies for the TRAB 360 show good pressure reduction from 20 to about 13.5, and reduction in ocular hypertensive medications from about 1 to 0.2. And less than one year postoperatively, 73% of patients were controlled on no medications. And now let’s look at gonioscopy-assisted transluminal trabeculotomy, otherwise known as GATT. So GATT is again a way of doing a 3630-degree opening of Schlemm canal to the anterior chamber. You are placing a device into Schlemm canal, and then opening the entire circumference of Schlemm canal. This is done with either a microcatheter, or a 4-0 nylon suture with the tip blunted. So this can be a very inexpensive procedure, if you’re using a suture. Less inexpensive if you’re using a microcatheter. And through that single goniotomy incision, you advance the catheter or suture 360 degrees, and then pull the ends to open the trabecular meshwork and inner wall. Sometimes you do need to reenter Schlemm canal, if you can’t go all the way around on the first pass. But most often, you can get 360 degrees with this procedure. A preliminary study of 85 patients who had GATT, by four surgeons — this is the group that actually developed this procedure for adults — found an overall decrease in pressure of 40%. At 12 months. So a reduction of 11 millimeters of mercury. No difference in pressure reduction with or without concurrent or prior cataract extraction. So this surgery is not in combination with phacoemulsification. Nor were the prior two. The GATT does not — was not studied in this case compared to phacoemulsification alone. And TRAB 360 and Kahook Dual Blade also have been studied in the absence of phacoemulsification. In a small retrospective review of subjects with juvenile open-angle glaucoma and primary congenital glaucoma, where 360-degree goniotomy has been shown to be effective, the pressure decreased from 27 to 15 over 12 months with a reduction in glaucoma medications from 2.5 to 1. Okay. Now we’re going to talk about canaloplasty or ab interno canaloplasty. Canaloplasty was introduced first. It’s a surgical technique that consists of taking down the conjunctiva, dissecting a scleral flap, removing a block of sclera to form a lake, and then entering Schlemm canal with a catheter and dilating the canal with viscoelastic, and then placing a tensioning suture in the lumen of the canal, with the aim of ultimately improving outflow facility, and lowering intraocular pressure. And this is the device that was used for that. There’s a rounded tip on the catheter. The catheter is 200 microns in diameter. And then the catheter contains a support wire to give it some stiffness. It has an optical fiber for light transmission. And then a polyimide tube to infuse fluid and aspirate. And so this device would be placed in Schlemm canal, canal dilated, a suture placed on the end of the device, and then the catheter pulled back through Schlemm canal, and with the suture tied off to cause tension in Schlemm canal, and that puts some stretch on trabecular meshwork, and the inner wall of Schlemm canal, as well as the outer wall. This is the suture in place, in cross section. So that is really not a minimally invasive glaucoma surgery. And the aspect of canaloplasty that can be minimally invasive, or microinvasive, is ab interno canaloplasty. So in contrast to traditional canaloplasty, that I just described, this does not require conjunctival or scleral dissection. And here, under gonioscopy, the microcatheter is inserted into Schlemm canal through an ab interno approach. There are no clinical trials published on this to date. And you can decide whether you’re going to do canaloplasty just dilating the canal, or actually do a GATT, where you take the two ends of the catheter and pull them across each other, opening the Schlemm canal 360 degrees. So this is sort of like the procedure I described just before, GATT, except that in ab interno canaloplasty, you’re simply doing viscodilation of Schlemm canal. In GATT, you’re actually tearing through trabecular meshwork and the inner wall to open Schlemm canal to the anterior chamber. Finally, Excimer laser trabeculotomy. And this procedure is not commonly performed. It requires a very expensive instrument. And the instrument also is mutagenic. This is an Excimer laser that can be delivered through an aqueous environment. It’s 308 nanometers xenon chloride, and this Excimer laser can be used to create microperforations in the trabecular meshwork. You can see how the procedure is done schematically here. And the procedure is done gonioscopically. It is not approved for use in the United States. It has been done in Germany and other places. But because of the mutagenicity of this wavelength of laser, I am somewhat concerned about this procedure. Especially since the intraocular pressure results are modest. This is even compared to SLT, selective laser trabeculoplasty. And you can see that by two years, the two procedures are very close, in terms of intraocular pressure effects. I’ll talk about a couple of devices for bypassing the conventional outflow system, and implantation in the suprachoroidal space. But first, how many have performed suprachoroidal shunt surgery? Answer one for yes and two for no. And the answers are coming up. And we see that most people have not performed suprachoroidal shunt surgery. 80%. And 20% have. So we really have two devices now for suprachoroidal space surgery. One is the CyPass, and the other is the iStent Supra. Let’s talk about the CyPass first. So this device was introduced, and it’s a fenestrated flexible microstent that is threaded through guidewire that follows the curvature of the sclera. Sorry. It is threaded through guidewire that follows the curvature of the sclera, enabling supraciliary bypass. It’s inserted through a single corneal incision. And the device is placed gonioscopically, and there is a cuff here at the top that maintains the stent’s position in the anterior chamber. And it’s composed of polyimide material. There have been several studies of the CyPass. And they were quite encouraging, reporting a very good reduction in intraocular pressure. And decrease in the number of medications required. And the COMPASS study was the largest and longest of those studies, and again, had a good intraocular pressure reduction and a great reduction in medications. With adverse events similar to phacoemulsification alone. However… It turned out on the five-year follow-up that there was significant reduction or loss of corneal endothelium. And because of that, the device was voluntarily withdrawn from the global market by Alcon, and the FDA issued a communication — the US Food and Drug Administration — issued a communication about the risk of damage to corneal cells following the CyPass procedure. So this procedure at this time is no longer being performed. In this study, 27% of patients had a more than 30% loss in corneal endothelial cell density. And it was correlated with the number of rings that could be seen. So the more anteriorly the device was placed, or left, the more likely it would be that there would be corneal endothelial cell loss. And for those of you who have implanted the CyPass, the recommendation is careful monitoring postoperatively, and the either trimming or removal if the corneal endothelial cell loss is occurring. Or if significant corneal endothelial cell loss is occurring. The trimming of the device is not easy. Because it is a stiff polyimide device. And the removal of the device is extremely difficult. Without causing damage to the tissue. So this presents a problem for those patients who have had CyPass devices implanted. Let’s talk about the iStent Supra. This is not available in the US at this time. But it does have a very similar appearance to the CyPass. And the future of this device is still uncertain. It has similar success to what was reported for CyPass. The corneal endothelial cell results have not been released. We can also reduce aqueous production with endocyclophotocoagulation. This really is not a new procedure. This procedure has been around for a while. Have you performed endocyclophotocoagulation or not? Yes or no. The answer should be up in a couple of seconds. This procedure has been around for 20 years. 80% of you have not done this procedure. 20% have. So endocyclophotocoagulation is a procedure consisting of an ab interno approach to diode laser coagulation of the ciliary processes, reducing the aqueous production in the eye and thereby lowering intraocular pressure. You really need to treat 270 to 360 degrees of the ciliary processes, and you want to treat them as completely as you can. You will invariably leave significant epithelial tissue behind, when the processes are treated, you see this whitening and shrinkage of the ciliary process. Here’s a normal process, right adjacent. Another normal process. So when you’re treating them, they shrink and turn white. And you’re still leaving quite a bit of epithelial tissue in between and posterior to the area that’s being treated. So the likelihood of developing hypotony or phthisis with endoscopic cyclophotocoagulation is quite low. There are no randomized controlled trials comparing ECP to traditional transscleral cyclophotocoagulation, but complication rates of ECP are lower in observational studies. It may similar to or a little bit less than trabeculectomy in the long term, and compared to a tube shunt procedure, ECP has similar outcomes in some cases. I would say that endocyclophotocoagulation is a reasonable choice in many patients, but there can be complications. Certainly more severe than with other minimally invasive glaucoma surgeries. And those complications could include cystoid macular edema, retinal detachment, and corneal injury, as well as iris injury. And this is from a prospective nonrandomized case matched study comparing ECP plus phacoemulsification versus cataract surgery with phacoemulsification alone, in patients with medically controlled glaucoma. And this was the study group, and this was the phaco alone group. So you can see that the success is certainly higher in this group, with the addition of the endocyclophotocoagulation. And then this is from a retrospective chart review, comparing ECP plus phaco versus phaco alone. The blue is ECP plus phaco, the light blue, phaco alone. And same here with regards to the number of medications. All right. The last thing that I want to talk about is bleb forming surgery. And in that area, I’d like to know how many who are listening have performed bleb forming surgery, other than trabeculectomy. If you have, answer yes. If not, please answer no. And the answers should be up momentarily. And it’s 50/50. Okay, so a lot more familiarity with the gold standard procedures, but some familiarity with the non-trabeculectomy bleb forming surgeries. So the two that I’ll talk about are the XEN-45 Gel Stent and the InnFocus MicroShunt. So first the XEN. Here is the XEN on this person’s finger tip. It’s a hydrophilic collagen tube with a 45-micron lumen. It becomes flexible when hydrated, so you want to put it in unhydrated, and the diameter of the lumen was selected to minimize risk of hypotony. With bleb forming surgery. This is preloaded into an injector. It’s supposed to be used for ab interno injection, where a keratome is used to enter the anterior chamber. The chamber is filled with viscoelastic, and then the device is placed on this needle, across the anterior chamber, and then through the angle, through the sclera, and emerges subconjunctivally, and then is injected through the needle so that a portion — 3 millimeters remains subconjunctival, 2 millimeters in the sclera, and 1 millimeter in the anterior chamber, ideally. There are some people who are using this device ab externo, but that is certainly off-label use. Time will tell which of the two uses is actually better. The device allows you to use an antimetabolite like mitomycin C, in order to increase the likelihood that the bleb that you create will survive. The early prospective studies use large lumen tubes that are not recommended, because of hypotony and flat chambers. The initial study of the XEN-45 showed good efficacy. So pressures in the low teens. And a good reduction in the number of medications. Small prospective nonrandomized case series with mitomycin C and phacoemulsification — you can see a good reduction in intraocular pressure, and a reduction in the number of medications. One issue with the XEN is the issue of encapsulation over the tip of the tube, subconjunctivally. In about 30% of cases, needling with mitomycin C, so a needle bleb revision with mitomycin C, is required in order to restore function to the XEN Gel Stent surgery. And the needling procedure is relatively straightforward. But the high rate of needling is somewhat unique to this particular device and procedure. And the last procedure that I want to discuss is the InnFocus MicroShunt. This is a new device that’s made of a material used in coronary artery stents. It’s been used in the body for a long time. Called SIBS. And the data on these implants are amazingly good. We’ll see once the device has been implanted in a large number of people what the results are, but the results that have been published so far — you can see starting pressures in the mid-20s, and final pressures in the low teens. So that is very encouraging. The InnFocus does require that the conjunctiva be opened in order for the stent to be placed. It’s an ab externo procedure only. So this is not a procedure that can be performed ab interno. And the material that’s used is what is unique for this device. And again, the early results are very, very encouraging. So what is the impact of all the different surgeries that we’ve been talking about? Well, you have to ask: Who is a candidate for microinvasive glaucoma surgery? And really for people who are going to have Schlemm canal surgery, you’re really talking about early to moderate glaucoma. This in general is not a surgery that you would perform on people with moderate to advanced glaucoma. Because the target pressure for the later group is going to be in the mid to low teens, whereas for the earlier group, you’re going to have a target in the mid to high teens. And so if you’re okay, the patient you think will be safe with the mid to high teens pressure, then Schlemm canal surgery may be appropriate for that patient. And you have this whole list of procedures that can be performed, and are likely to achieve that sort of target pressure on average. For patients who are having Schlemm canal surgery, this is a controlled way of lowering intraocular pressure, so the biggest advantage is that there’s less risk than with trabeculectomy or with a glaucoma drainage device implant. You don’t have the same degree of risk of scarring and endophthalmitis that you do with those surgeries, when you’re doing Schlemm canal surgery. But the trade-off is that there’s less pressure reduction than those more invasive glaucoma procedures. The safety of the ab interno Schlemm canal surgery allows implementation of these procedures earlier in the treatment regimen. So in many countries, I’m sure for many of those who are listening, glaucoma is primarily a surgical disease. And so in patients who have early to moderate glaucoma, these offer an excellent option. If medications are available, you may choose to use medications before introducing these operations, but if medications are not available, or follow-up is going to be poor, or adherence to therapy is going to be poor, these surgeries are not a bad choice. That does not mean that selective laser trabeculoplasty or argon laser trabeculoplasty would not be appropriate prior to introducing these surgeries. It would depend on the patient, and every patient is unique. So these are just general rules that I’m stating. But efficacy issues really restrict these surgeries to people with mild to moderate disease. For people who have moderate to advanced glaucoma, you really want a target pressure in the low to mid teens, and there we’re talking about a bleb forming procedure like the XEN Gel Stent or the InnFocus MicroShunt if you’re going to do the minimally invasive glaucoma surgery techniques or a trabeculectomy or a glaucoma drainage device. The advantage of the XEN and the InnFocus is that they are less risky than trabeculectomy or a glaucoma drainage device. On the other hand, it is not clear that the efficacy with these devices is at the same level as trabeculectomy or glaucoma drainage device. So which MIGS is best for which patient? Well, if you have a patient like this one, where you have early to moderate glaucoma damage, here a mean nerve fiber layer thickness of 72, the patient is getting worse, although not very quickly, and not a tremendous amount of damage — again, this is a patient for whom minimally invasive glaucoma surgery might be appropriate. On the other hand, a patient like this would do better with a bleb forming surgery. Bad glaucoma, getting worse fast. In these patients, a bleb forming operation would be the best choice for the patient. Thank you very much. I will be happy to take questions. So the first question is whether it’s absolutely necessary to use antimitotics for an effective glaucoma surgery. And the answer is usually yes. If you’re going to do a bleb forming surgery, your best bet is going to be to use an antimitotic. In general, for any glaucoma surgery, with the exception of a glaucoma drainage device like a Molteno or an Ahmed or a Baerveldt, the antimitotic is going to be necessary for success. And so I would say yes for the bleb forming procedures. The second question is: How can patients with advanced glaucoma benefit from MIGS? And as I mentioned, MIGS, using the XEN Gel Stent or the InnFocus MicroShunt are useful, even in people who have advanced glaucoma. And so I do use these procedures, and many people do, in that setting. So it all depends on what your target pressure is. If your target pressure is in the low teens or low to mid teens, then you need to go with a bleb forming procedure to be likely to achieve that pressure. If your target is in the mid to high teens, then Schlemm canal surgery would be appropriate. The third question is: How deep do you go in sclerectomy? And so in a deep sclerectomy, you go 90% thickness. In a trabeculectomy, you go about 50% thickness. So if you’re doing a trabeculectomy, you want to make your trabeculectomy flap about 50% thickness, and maybe you’ll make it about 3×3 millimeters — some people like to make it a little smaller, some people like to make it a little bigger, some people like to make it triangular, some trapezoidal, some square. It doesn’t matter. It matters that you have adequate thickness to restrict flow, and it matters that the trab flap is big enough to cover the sclerotomy. In a deep sclerectomy, you make the initial trab flap, and then you make the additional 48% flap after that. Next question: How does one go about patient selection for MIGS? So patient selection for MIGS is based on the severity of the patient’s disease. And whether or not the angle is open. If the angle is closed, doing angle surgery is much more difficult, and it’s not obvious that you are going to get the same results with angle surgery as you do in patients who have open-angle glaucoma. Also in neovascular glaucoma, it’s not clear that you would get the same sorts of results as you do in open-angle glaucomas, and in ICE, the same story. It’s not clear you would get the same benefit. So with those patients, you might want to go with trabeculectomy or tube implant or one of the bleb-forming MIGS. But for the most part, for Schlemm canal surgery or for suprachoroidal space surgery, you want to have a patient who has early to moderate disease. The next question is how effective is MIGS, compared to traditional trabs. And so with a traditional trabeculectomy, you can expect to get a final intraocular pressure in the low teens. Maybe even the single digits. And those numbers are necessary for patients who have advanced disease. So MIGS are not going to get you there, unless it’s the bleb forming MIGS procedure. And if it’s Schlemm canal surgery, it’s very unlikely that you will achieve that sort of pressure. The next question is: How will MIGS reach the developing world? And I think that the answer to that has to do with a number of factors, and cost is not an unsubstantial factor. So things like the Kahook Dual Blade really make it possible for people in the developing world to perform MIGS, since the device is a type of a knife or a blade, and does not require machinery. So it’s a much less costly way to remove the trabecular meshwork and the inner wall of Schlemm canal than the other ways of doing that procedure. And it is not a device that you leave in the eye. So you don’t need hardware left behind, in order to perform that procedure. So I think that that is one type of MIGS that has the most facile entry into the developing world. Now, many of the patients in the developing world have very bad disease. They may not be seen until their glaucoma is quite advanced. And so for those patients, the Kahook Dual Blade is not a good choice. And if the implants, like the XEN and the InnFocus MicroShunt, are not available to you, trabeculectomy is really going to be the best option, or a glaucoma drainage device, if that’s available. But I would say that economics has a lot to do with the ability to reach the developing world.
So the first question is: What’s the best option for neovascular glaucoma? And I believe that neovascular glaucoma is usually best treated with a glaucoma drainage device, although there are certainly plenty of cases that do well with a trabeculectomy. Also, if the glaucoma damage is very bad, in the patient with neovascular glaucoma, trabeculectomy is the only thing that’s going to get the pressure low enough to protect the optic nerve. On the other hand, that type of glaucoma is notorious for causing scarring and failure of the trabeculectomy bleb. So you want to make sure you’ve treated the neovascularization and the inflammation associated with it, prior to performing the trabeculectomy, if at all possible. The next question is the cost of stents. And so that is going to depend on your location. The stents in the US cost anywhere up to $2500 or more, for some of these implants. And so it is not an inexpensive venture to perform MIGS with these devices. But the actual cost is gonna depend on your location. The next question is: Is it a must to combine MIGS with cataract surgery? And the answer here has to do with economics again. So in the United States, most of the MIGS implants are approved for use with cataract surgery, because that’s how the clinical studies were performed. And that is how they’re approved by the FDA. So the payers in general will only pay for the device if it is implanted in conjunction with cataract surgery. Some of these devices do not require cataract surgery in order for the insurer to pay for the operation. But many of them do. And so that is a complexity that has to do with the US payment system for medical care. The next question is: When do you choose MIGS over SLT in your patients with mild to moderate glaucoma? And personally, I perform SLT if I think that I am likely to achieve the target pressure with that procedure. So if I think that the SLT is likely to be successful and adequate, I will perform that. If it fails, then I might move on to MIGS. But if I have a chance to control the pressure with a less invasive, less risky procedure, I would prefer to do that. Next question is: What should one prefer for early glaucoma? MIGS or laser? I think that’s the question that I just answered, although this one looks at SLT and micropulse. So here we’re talking about a stimulatory procedure. SLT stimulates the trabecular meshwork to improve its function and lower intraocular pressure in that way, whereas micropulse is a cyclodestructive procedure. It also may cause some more porosity or increased outflow through the unconventional outflow route, and the inflammation caused by micropulse may also have some effect on the trabecular outflow. But I would prefer to perform SLT in a patient, and I usually reserve micropulse to later in the treatment course, if that patient has failed incisional surgery. Or if the patient is too sick to undergo incisional surgery. Then I would consider micropulse or conventional transscleral cyclophotocoagulation. The next question is: What about its effectiveness on black patients? So for the Schlemm canal surgeries, the effectiveness appears to be similar in black patients and in non-black patients. For the bleb forming surgeries, for black patients of African origin, it is much more risky for the black patient than the white patient in terms of the likelihood of failure, due to scarring. So much more reactive conjunctival and episcleral tissue, and therefore those patients have to be watched more closely, and may need neobleb revisions, or may need another or a second operation in order to be successful. And so that is certainly a consideration, any time that you’re operating on black patients, especially of African origin. The next question is: In GATT or angle surgery, how do you manage if bleeding occurs at the time of cutting trabecular meshwork? So it’s typical that bleeding will occur at the time that you enter the Schlemm canal, or when you depressurize the eye, if it hasn’t occurred at the time that you entered. If you have a relatively high pressure during the entry period, it does make it a little bit more difficult, because Schlemm canal collapses a bit, so the lower pressure allows you to visualize Schlemm canal from red reflex, and also that gives you a target. But it also does result in a little bit more bleeding at the time of device placement or removal of the trabecular meshwork tissue. If you do have bleeding, you can pressurize the eye, and you can use viscoelastic to try to clear the area, and if that’s not effective, you may either need to move to a different area or a different procedure. The next question is: Can repeated MIGS procedures be performed? And the answer is: It depends on which procedure. So if you’ve put in an iStent or iStents, then yes. You can perform removal of the trabecular meshwork to open Schlemm canal, you can perform GATT or TRAB 360 or canaloplasty. If you’ve removed the trabecular meshwork and inner wall, your options are really limited. There you can remove the remaining trabecular meshwork and inner wall that you have not removed with the initial trabectome or Kahook blade procedure, or you can do a bleb forming procedure, or you can do a suprachoroidal shunt. The next question is: How many procedures can be done with a single Kahook blade? And the answer, at least in the US, is one. The fact is that the blade may still be sharp enough to do additional procedures, but it’s a single use device in the United States, and it’s labeled that way. And so we can only use it once. But we know that there is a lot of waste in the medical system, and many devices that are labeled for single use actually are good for repeated use. So that’s a longwinded way of saying I don’t know. But I’m sure that the procedure can be done effectively more than one time with a single blade. The next question is: Can MIGS be done for congenital glaucoma? And the answer there is yes. But what you want to do in those patients, really, is open Schlemm’s canal, and so the use of GATT or TRAB 360 is a good option in people with congenital glaucoma, as opposed to a simple goniotomy, which could also be done. The success rates are higher for the GATT or TRAB 360, but goniotomy with a blade is useful, because the tissues fall back in congenital glaucoma, unlike in adults, or you can use the Kahook Dual Blade or the trabectome in that setting, and that works as well. But you’re not opening up as much of the angle as you do with the GATT or the TRAB 360. Thank you very much. I think that’s everything.

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February 12, 2019

Last Updated: October 31, 2022

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