Angelo P. Tanna, MD: Let’s discuss the indications and patient selection for the various new procedures available for the surgical management of glaucoma. I also want to address possible long-term adverse consequences that may result from angle surgery.
Let’s start by talking about a device we have readily available to us right now. When do you use the iStent?
Davinder S. Grover, MD: If a patient has very mild disease, controlled on one or two medications, iStent has some utility. Good evidence exists that cataract surgery in glaucoma patients can cause a spike in pressure within the first four to six hours. I tell my patients the iStent will likely minimize the chance of a pressure spike in the immediate postoperative period.
If the iStent can minimize the patient’s dependence on drops, even by one or two, that’s a great win. I think the risk is minimal when the device is used appropriately.
Dr. Tanna: Define mild disease. A mild visual field abnormality?
Dr. Grover: I don’t have any strict criteria. Generally, I consider using an iStent if the patient is controlled on one or two medications and if the patient has a mean deviation of about -3 dB or better.
Dr. Tanna: How about a patient with ocular hypertension in whom the field is normal?
Dr. Grover: If I’m suspicious enough to put a patient on medical therapy, I would consider it.
Dr. Tanna: That would be off-label. Have you had reimbursement problems?
Dr. Grover: None that I know of.
Dr. Tanna: Tom, what do you think?
Thomas W. Samuelson, MD: I agree, except I expand my indications considerably deeper. You have to gauge them based on your existing alternatives. I would do phaco plus a canal device all day long to try to avoid phaco-trabeculectomies, knowing I haven’t decreased my chance for success should a trabeculectomy be required down the road.
I tend to do a lot of phaco-iStent procedures with one or two devices. I don’t see glaucoma severity as much of a determinant of my indication as I do the degree to which it is controlled. So, for example, I do phaco-iStent for patients who have more severe field loss, but stable fields, for the last five years, with reasonable pressures. But, perhaps they’re on four medications; then I may get them down to one or two medications and they’re still controlled because they were before, but now they’re on a much more manageable drop schedule.
We now have options that are extremely safe, and we’re trying to figure out where they fit in, but in my view we don’t skip interventions because glaucoma is too severe. If we think the glaucoma is too uncontrolled for a step to be meaningful, we might skip it. But severity doesn’t equate to control. You can have mild disease that is severely out of control, and you can have severe disease that is well-controlled. Everything we do in glaucoma is an incremental step, and phacoemulsification combined with a canal procedure is an incremental step. It is safe and can have very favorable effects in a subset of the population. We need to get better at identifying the best candidates.
So I have expanded my indications for iStent, and we’ll work other newer canal procedures in as we go. There will always be some patients for whom the canal just isn’t an option, so we’ll use other reservoirs like the suprachoroidal space or the subconjunctival space.
Dr. Tanna: If you have a patient with moderate to severe glaucoma who has a cataract, and you think that a trabeculectomy may be required at some point in the future, the earlier you get the cataract out, the better for the patient. We know fairly well that the success rate for the trabeculectomy is a little bit worse when you combine it with cataract surgery. And if you postpone phacoemulsification, then the trabeculectomy is in danger when you do that cataract surgery in the future. So the idea of getting the lens out and implanting a canal device to postpone — or maybe completely eliminate — the need for some more intensive intervention in the future is a pretty valuable approach.
What do you think, Rick?
Richard Lewis, MD: The studies were restricted to mild and moderate glaucoma damage based on visual field and optic nerve changes without regard to IOP. There’s a disconnect in that terminology. I probably wouldn’t do an iStent on a patient whose pressure is 15 mm Hg and who is losing vision. For a patient with ocular hypertension taking two medications, I think an iStent is a great way to go. And I also agree with everyone about taking the cataract out. By far our safest surgical approach is taking the cataract out, and it’s probably the single best treatment for glaucoma.
The issue is identifying the best procedure for the target pressure. Data from CyPass, iStent, Hydrus and XEN that have been released in the past couple of years can help with this. I disconnect the severity of the glaucoma with the target pressure.
Dr. Samuelson: If a patient has a rapid rate of progression, I’m more likely to be more aggressive.
Dr. Tanna: Primary trabeculectomy gets you the lowest IOP.
Dr. Samuelson: Perhaps, or instead of putting in a focal canal device I would consider a 360°, ab-interno unroofing of the canal. I think it has a chance to result in a more significant pressure reduction, but it’s also more tissue-disruptive.
Getting back to your original point about long-term safety, what will the consequence of that be five years or 10 years down the road? It’s hard to say. Many of our other surgical interventions completely abandon the outflow system. So if we gain a significant length of time with improved pressure control but have some downstream adverse effects due to scarring, we still come out ahead.
Dr. Tanna: Davinder, your group developed ab-interno trabeculotomy (gonioscopy assisted transluminal trabeculotomy, GATT). This procedure causes extensive disruption of the drainage system. Your thoughts on potential long-term adverse effects?
Dr. Grover: I am comfortable with GATT because it’s a less invasive modification of ab-externo trabeculotomy, a surgery that’s been around since the ‘50s. We have seen patients fail, but we haven’t seen them become worse than before the surgery. If it’s not going to work, they’re probably going to be where they were before we performed GATT. GATT is not excessively disruptive to the drainage system; however, it does cleave the trabecular meshwork 360°. Some patients do fail despite having an open trabecular shelf. In these cases, there’s obviously some downstream canalicular scarring or resistance. We’re at an infantile stage in our understanding of the entire outflow pathway; however, in our hands, GATT is a safe and effective method of treating various types of open-angle glaucomas.
Dr. Tanna: We all have patients who as infants had trabeculotomy for congenital glaucoma who are doing well at age 30 or so. So, that speaks favorably for the long-term potential of GATT. What are your indications for GATT?
Dr. Grover: I have seen patients in whom at the time I perform the initial goniotomy incision, the iris starts to move. It is almost like there is a continuous membrane over the trabecular tissue down to the iris. I think juvenile-onset open-angle glaucoma eyes, that is patients diagnosed with glaucoma in their 20s to 40s, respond particularly well to GATT.
Dr. Samuelson: When I left my fellowship, if a patient didn’t have a pale diffuse bleb and a pressure of 8 to 12 mm Hg, I was disappointed. But over time, I have learned that a pressure of 15 mm Hg on one medication is not a bad outcome for most patients.
That is where many of these MIGS procedures can play a major role. We do have that subset that needs single digits, but if we intervene surgically earlier instead of treating with three and four medications and continuing on until toxicity, with earlier intervention some patients won’t need the single digits. In the future we may get by with the best of MIGS and medications: combining your MIGS procedure of choice with an easily administered medication.
Dr. Grover: The most exciting thing about these new surgeries is that there are more barriers before I have to do a filtering procedure.
Dr. Lewis: Our experience with the MIGS procedures has made us more adept in the use of a gonioprism in our nondominant hand, and we are better at positioning the patient and getting optimal visualization. Mastery over these nuances has led to optimization of our outcomes.
Dr. Tanna: Trabectome, the Kahook dual blade, GATT, Hydrus and iStent aim to bypass trabecular meshwork resistance. How does one choose which to use?
Dr. Grover: I don’t see a substantial difference between Hydrus and a limited segmental goniotomy or a trabeculotomy with the Kahook dual blade. I’ve been moving away from Trabectome due to its complex set-up and the electrocautery.
Dr. Samuelson: The comprehensive cataract surgeon is unlikely to do many 360° ab-interno trabeculotomies. So, I do think that the canal devices are probably more conducive to a wider surgeon population.
I think the Hydrus does two things. It provides a direct inlet to the canal, as does iStent, but it also scaffolds an 8-mm segment of the canal. Work with canaloplasty shows that the tension in the canal seems to help physiologic outflow as well.
Dr. Lewis: I think the Hydrus and the iStent are minimally disruptive to the trabecular meshwork and canal. Kahook dual blade, GATT and the Trabectome are very destructive to the meshwork. Now, you could argue, “the meshwork is dysfunctional so fine just get rid of it,” but I wonder if we are going to see a lot of scarring and perhaps renewed pressure elevation two or three years later.
Dr. Samuelson: That question is really important if you start doing these procedures on patients with ocular hypertension, or mild disease, because there’s a chance it can make them worse. However, implanting a very localized stent in conjunction with cataract surgery is less likely to make them worse.
Dr. Tanna: Hydrus and iStent have both been associated with the development of PAS even when properly implanted.
Dr. Grover: What’s the effect of a metallic foreign body in the canal in vivo? We know nothing about wound healing in the canal, or what a device does to the canal long-term, or about the difference between ablation and tearing the canal open.
Dr. Tanna: It is safe to do an MRI in a patient with an iStent or the Hydrus with a magnetic field up to 3 Tesla. CyPass is nonmetallic. Davinder, you’ve published your results with GATT — you use GATT for older patients with glaucoma as well.
Dr. Grover: GATT has essentially revolutionized how we take care of glaucoma patients. For eyes with very, very mild disease, we’ll consider an iStent. But, for moderate to advanced disease, we will do GATT, either with a catheter or for more cost-effective delivery of health care with a 5-0 Prolene suture with a blunted tip.
It’s a well established surgery. We have good safety data on trabeculotomy for 30 to 40 years, and we’re just doing it in a less invasive and safer way.
Dr. Tanna: Do you have any pearls for performing GATT?
Dr. Grover: I use a 25 MVR blade to make a 1-mm goniotomy so I can see the outer wall of the canal. That’s actually how I put my iStents in now too.
The iTrack microcatheter loves to go in and around the canal. But, if it gets stuck, it’s likely to stop at about 270° or the point of maximum resistance. What I typically do is make it so my 270° point is always at 6 o’clock. For left eyes I go clockwise, and for right eyes I go counter-clockwise. If the catheter or suture fails to advance at 270°, that will be 6 o’clock. Then I can move the head of the bed, cut down and retrieve it.
Dr. Samuelson: You prefer GATT to the Kahook dual blade?
Dr. Grover: I use the Kahook blade in patients with mild to moderate glaucoma or slightly active inflammation. I had a gentleman with bilateral scleritis with an IOP in the 40-mm Hg range in both eyes on maximum medication. GATT would have probably been too much for this eye, while it was inflamed. I did an ab-interno trabeculectomy with the Kahook dual blade. It creates a limited opening, is less traumatic and is associated with a lower chance of bleeding. The patient did quite well. I don’t use GATT for patients with inflammation or patients who can’t be taken off blood thinners.
Dr. Tanna: Do you do many trabeculectomies as a first surgical procedure?
Dr. Grover: Yes. When we analyzed our two-year data, we found that doing a GATT has roughly a 90% chance of failure in POAG patients with a mean deviation of -15 dB or worse. These patients need a pressure of 10 to 12 mm Hg and, given their advanced disease, do not have an intact collector system. So if they’ve very advanced disease, I would do a primary trabeculectomy.
Dr. Tanna: You have written about the episcleral fluid wave as an indicator of success after canalicular bypass surgery. What have you observed with GATT?
Dr. Grover: After GATT, I try to get an episcleral venous fluid wave. I’ll repeatedly pump BSS [balanced saline solution] in the eye; the behavior of the eye during that phase is instructive. With each additional time I pump BSS, the episcleral fluid wave will appear more rapidly. It’s almost a therapeutic maneuver. It’s diagnostic and therapeutic.
Dr. Lewis: Maybe that’s why the pressure comes down after high-flow phaco. It may enhance the outflow system ... I think you’ve convinced me I’ve got to start doing GATT. It’s really interesting.
Dr. Grover: What I do now if I use the microcatheter, because of the theoretical potential benefit of viscodilation, is as I’m going around the canal for my GATT procedures I’m asking my assistant to click every two to three clock hours, so I’m viscodilating as I’m going around. When I get around, I open the canal as usual at the end.
Dr. Samuelson: So you’re doing that for the downstream benefit?
Dr. Grover: Yes. I think it opens up these small obstructions; otherwise you’d likely get caught, so it makes it easier to get around. When you make the goniotomy incision you get blood. Instead of coming out, I have my assistant click and it’s like a fire hose.
Also, none of my colleagues viscodilate during GATT. We haven’t found the outcomes to be vastly different.
Dr. Tanna: So you do most of your cases with the microcatheter.
Dr. Grover: Yes, for many of my phaco GATT cases.
Dr. Lewis: What code are you using?
Dr. Grover: 6174 if I use the catheter that is viscodilation without retention suture. I use 65850, the trabeculotomy code, if I don’t use a catheter. OM