An Introduction to MIGS for the Retina Specialist

Considerations for managing patients with new glaucoma devices and surgeries.


In this roundtable discussion, glaucoma and retina specialists discuss minimally invasive glaucoma surgery (MIGS) to provide some foundational information to retina specialists about MIGS devices. Glaucoma specialists Michael Greenwood, MD, from Vance Thompson Vision in Fargo, North Dakota, and Jonathan Myers, MD, chief of the glaucoma service at Wills Eye Hospital in Philadelphia, Pennsylvania, join retina specialists Mark R. Barakat, MD, a vitreoretinal specialist at Retinal Consultants of Arizona in Phoenix, Arizona, and moderator Yasha Modi, MD, a retina specialist and assistant professor of ophthalmology at NYU Langone Health in New York, New York.

Dr. Modi: Dr. Greenwood, would you give us an overview of the new MIGS devices and their implantation procedures?

Dr. Greenwood: There’s been an explosion in MIGS procedures in the last few years. It began with a focus around trabecular meshwork bypass with the Glaukos iStent in 2011. The second-generation iStent also bypasses the trabecular meshwork. The Cypass device by Alcon went into the suprachoroidal or supraciliary space, but it was withdrawn from the market in 2018 due to safety concerns with the cornea. Allergan’s Xen gel stent is a filtration surgery, but we do it very minimally invasively without really cutting any tissue. There are also surgeries to remove the trabecular meshwork or doing some stenting through the Schlemm’s canal to make the outflow pathway flow a little bit better. So, there are 3 targets: the trabecular meshwork, the suprachoroidal and supraciliary space, and the subconjunctival space, with several options for all of those. There is also the Hydrus stent by Ivantis, which is a long bypass device. It is still pending insurance coverage, but it was recently approved.

Dr. Myers: I think it might also be helpful for retina specialists who don’t hear the terms every day to know some of the goniotomy or trabecular bypass procedures that don’t involve devices. These include the Kahook dual blade (New World Medical), gonioscopy-assisted transluminal trabeculotomy (GATT), Trab 360 or Omni 360 (Sight Sciences), and ab-interno canaloplasty (ABiC).

Dr. Modi: What are the common complications that you see from trabecular bypass MIGS procedures?

Dr. Greenwood: The biggest complication that comes to mind with trabecular bypass is bleeding. This doesn’t happen all the time, but it does happen. And as you know, a little bit of blood inside the eye feels like a ton of blood for the patient. There is big debate in the glaucoma space on whether this is hyphema or blood reflux. For the most part, it’s blood reflux, which is less of a problem than hyphema. When we put the device in, it eventually leads to the episcleral veins, which serve as a safety stop for the drainage system so we don’t get hypotonous. We do see a little bit of blood reflux but usually that stays in the anterior chamber. If someone has loose zonules, or easy access to the posterior space, the bleeding can get into the vitreous and that can take longer to clear. Other than bleeding, everything else is very minor or very transient.

Dr. Modi: Because patients still have Cypass in the eye, what complications do you see with suprachoroidal shunts, and can this affect the posterior segment?

Dr. Greenwood: Hyperopic eyes can get a slightly enlarged cleft or myopic shift from the implant. There can also be choroidal detachments, but it’s such a limited choroidal that you can’t really see it on straight examination.

Dr. Myers: Sometimes you can see the cleft and a little bit of an effusion anteriorly or posteriorly in some of these cases, and they can range. Luckily, in the vast majority of cases, they go away on their own. But we’ve had a couple of eyes referred into us that were persistent and even with surgical repair were fairly challenging.

Dr. Modi: Dr. Myers, you mentioned an enlargement of a cleft. What are some of the management options in a situation like that for suprachoroidal surgery, and what often is the role of the glaucoma specialist and the role of the retina specialist in managing it?

Dr. Myers: Well the “great” thing about new devices is we find new ways to create complications. The clefts don’t occur just with the suprachoroidal shunts. Unfortunately, there are times when less experienced surgeons, or experienced surgeons with difficult patient situations like patient movement, will inadvertently create a cleft even with an angle procedure like a goniotomy, or even a first-generation iStent. Our repair that we do typically for a nonstented cleft, a cleft without a Cypass, is an internal approach if they’re pseudophakic. I call it a bucket handle approach, in which a double armed Prolene suture is passed behind the iris to tent the iris tissue from behind up against the sclera, coming out through the sclera and tying on the scleral surface in a groove or under a flap. We do that, and there’s also the sewing-machine method that’s been popularized for larger clefts where you do multiple passes with one running suture.

External cleft repair can also be done in which you create a scleral flap, underneath which another incision is made to access the ciliary body. Suturing the ciliary body to the sclera through this deeper incision closes the cleft. The scleral flap and conjunctiva are then closed above. This can help close larger clefts from the outside, especially in phakic patients. That’s a bit more laborious, but it can be effective in the more challenging clefts. Some surgeons have also had success putting large capsular tension rings into the sulcus and using those to hold pressure to close a cleft long enough to seal it off.

The problem is in the setting where you have a Cypass still in position, it’s more questionable what you do. Removing the Cypass sometimes can be easy, but sometimes it can be fibrosed in and hard to remove. Some of my colleagues at Wills Eye Hospital have removed the Cypass and closed the cleft, or left the Cypass in place and run sutures up to the Cypass on either side to try to tie things down to both sides. It’s a little more challenging sometimes with the stents in position.

Occasionally, retina surgeons may be confronted with loose devices that have become free-ranging devices within the eye because of complicated situations. The first-generation iStent is about 1 millimeter, but the iStent inject is only about 0.3 millimeters long and is not magnetic because it’s titanium, and so would be challenging to find. Ultrasound can be helpful preoperatively to find it, but that can be challenging. Luckily, it’s very rare because surgeons are so good these days in terms of the insertion and the placement.

Dr. Modi: Could we talk about bleb-related procedures where maybe IOP reduction is more, and that puts patients at risk for hemorrhagic choroidal detachment, hypotony, and even potentially hypotony maculopathy?

Dr. Greenwood: The only bleb-related device available right now is the Xen gel stent. It’s a subconjunctival device. We can place it from inside of the eye going out, or outside the eye going in. But either way, you get a bleb formation. And the device was developed in such a way that it doesn’t have a valve on it, so there isn’t any restriction to outflow, but the fluid flow is so controlled and slow because the inner diameter of the lumen only allows so much fluid to flow through. In theory, this prevents hypotony from happening, but it still can happen. Sometimes with these patients there will be a numerical hypotony where the pressure is 6 mmHg or lower, but the chamber is still formed. Because they have a rigid sclera with decreased pressure, these patients can develop some of the choroidals and macular folds that you have to manage in the short term. But usually this is self-limiting. With conventional glaucoma surgeries we might have to refill the chamber with viscoelastic.

Dr. Myers: Like most glaucoma surgery, long-term failure is more common than hypotony. In the event that these stents do create hypotony, it’s sometimes because of flow around the shunt as much as flow through the shunt. A retina surgeon might also be referred a case of bleb-related endophthalmitis from a Xen stent, but that doesn’t seem common at all now. However, there have been cases of erosion, so it’s worth looking at these stents where they exit 2-3 mm back from the limbus because that’s the place you might see a conjunctival erosion. For a patient referred for an endophthalmitis or infection after any type of hardware surgery, it’s worth making sure there’s not an eroded device that needs to come out and a leak that needs to be repaired. Thankfully, that’s uncommon with the Xen, but it has been reported.

Another thing to be aware of is a new device coming to the market soon, the Microshunt (Santen), which will be marketed under the name Preserflo. We expect this device to be a little bit more effective but we will have to see if there is more risk for choroidal effusions in the early postoperative period.

Dr. Modi: Dr. Barakat, as a retina specialist what complications of these devices have you specifically been referred? What have you seen in your practice, and what has been your management strategy?

Dr. Barakat: These are honestly few and far between. Probably the most common one is a little bit of vitreous hemorrhage. If the vitreous hemorrhage isn’t too dense and they can see well enough, patients probably never even come to see me. But if it’s a concern that there might be retinal pathology hidden behind it, it’s never a bad idea to have someone come take a look as well. But management has been pretty conservative. I think the biggest mistake a retina specialist can make is to be overeager to operate in these situations. Of course, ultrasound if necessary, and a good examination is key, but usually it’s self-resolving. I’ve been on the lookout for choroidal detachments, but I haven’t seen too many of those either. I imagine the strategy for that would be very similar to traditional filtration surgery, where unless it’s threatening the central vision or there is a choroidal, then observation is key and the hemorrhage usually resolves quite nicely.

Dr. Modi: Dr. Barakat, I also wanted to address the fact that a lot of these procedures are combined with cataract surgery. I think we’re all very familiar with pseudophakic retinal detachment that occurs a few months after cataract surgery that has gone beautifully. In any of these procedures, is there anything that you do differently at the time of your retinal detachment repair that you otherwise wouldn’t do?

Dr. Barakat: Not too much. The only difference is if it is a bleb-based procedure, then I take care to avoid that when I’m making my incision. I don’t want to destroy their work. I make sure that when we do the vitrectomy that the hyaloid is elevated and I have identified all of the relevant peripheral pathology.

Dr. Myers: Dr. Barakat, have you found anything different in patients with prior MIGS surgeries in the setting of cataract surgery? Have you seen pressure spikes or management issues in cases of retained lens or dislocated IOL?

Dr. Barakat: No, I haven’t seen much difference in terms of pressure spikes. Usually when patients come to me with retained lens fragments, the first scenario is that most of the retained lens fragments are still in the eye. In this case, many times the MIGS procedure was aborted. But if there are a few lens fragments that are chronically left behind in the eye, we really haven’t seen any shifts in intraocular pressure based on that.

Dr. Myers: Among glaucoma specialists we discuss whether a more dynamic operative situation increases the possibility of these devices coming loose, but we haven’t seen that.

Dr. Barakat: The thing I would be wondering about is more surgical trauma at the time of the initial cataract surgery. I wonder if the inflammatory burden is higher, but that’s very hard to really elucidate based on lens fragments in the eye.

Dr. Modi: When there is a cataract complication and retained lens fragments, is it customary to proceed with MIGS or not?

Dr. Greenwood: Great question. It depends on surgeons’ comfort level and the specifics of the case. If there is a complication but there is still a good view of the angle, I would go ahead and put in the MIGS device. If it’s just a lens fragment that went back, you know you’re not damaging or putting anything at risk in the angle. If you can finish the case from the cataract standpoint and put in your glaucoma device, then that’s a win for the patient, because often these patients have pressure spikes afterward, usually from retained viscoelastic. And they already have glaucoma, and they still have a long life to live after everything settles down from the initial surgery. So if they only have 1 drop, you can still give them that opportunity to get off their medications or better control their pressure.

Dr. Modi: I’d like to talk about one additional complication that we all have seen in traditional glaucoma surgery and that is aqueous misdirection or malignant glaucoma. Is that something that we’re seeing less frequently with these various MIGS devices? And is there any alteration for the traditional management of aqueous misdirection in these eyes relative to more traditional procedures?

Dr. Myers: We have had the displeasure of seeing it with almost all the devices at this point. But I should say that compared to when I started in the ’90s, malignant glaucoma is much less common now. I think that the flaps are tighter today than in the ’90s and we have fewer episodes of shallow chambers that need reformation. And we’re a little more hypervigilant about the eyes that are at risk in terms of tying them tighter, for patients who start with higher pressures, the shorter eyes, the angle-closure glaucomas. I think the extra care and precaution goes a long way there. That being said, the MIGS procedures all have much greater restriction of outflow compared to trabs and tubes, so my impression is that there is less potential for aqueous misdirection with these devices, although it can occur with MIGS. But of course I’ve seen aqueous misdirection after straight phaco surgery in short eyes too. Some eyes are predisposed enough that it still can happen, but thankfully it is happening less often.

Dr. Modi: How about long-term potential complications retina specialists might see after MIGS procedures? Because mitomycin C is used in the Xen procedure, do the blebs look intrinsically different than trabeculectomy? Might there be progressively thinner and more avascular blebs over time? Is there a long-term risk of late bleb-related endophthalmitis?

Dr. Myers: We’re hoping that these lower, more posterior blebs are at low risk. There are some reasons that people are hopeful, but there are no data to go along with that. However, it’s an excellent point you bring up because I’d say that especially early in the Xen learning curve, some patients who had higher doses of mitomycin C when it was closer to the limbus have had more avascular perilimbal areas diffusely over the superior-bulbar conjunctiva than we all would have wished. So if retina surgeons see very white conjunctiva and sclera, they should not place sutureless pars plana vitrectomy ports there. Vascular tissue is a great place to go with those.

Dr. Barakat: As for bleb-related endophthalmitis, in the future we’re going to be seeing more of these MIGS patients. Typically I try to manage endophthalmitis medically, and if it’s a particularly virulent bacteria, of course, then surgically. Is there a concern for seeding of the device? If so, before I even go into the operating room, do I need to have a glaucoma surgeon with me to take the device out?

Dr. Myers: Great question. I don’t know the answer. What we do for the most part is leave hardware on the first go around. This seems to work out with tube shunts, unless it’s an erosion over the tube shunt that led to an infection that really looks tube shunt based. We wind up leaving the hardware and people don’t need secondary procedures. But that experience is based on a handful of cases, not hundreds. So I’m open to other thoughts and opinions or experiences on that.

Dr. Greenwood: I don’t have any experience with that, thankfully. I’m in private practice in the middle of North Dakota, so our population and practice are a little bit different here than in the center of Philadelphia, but I agree with your method. If you can leave it in, leave it in. Some of these are so small they are hard to take out. You don’t know what’s grown into the fenestration. So if you can keep it in, that would be great. But if it continues to have issues then yeah, you would probably get it out of there, like an IOL. That’s the way I look at it.

Dr. Modi: Thank you all for your excellent contributions to this discussion. RP