October 21, 2019
9 min read

Patient type, surgeon comfort level help guide glaucoma surgery choice

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Welcome to another edition of CEDARS/ASPENS Debates. CEDARS/ASPENS is a joint society of cornea, cataract and refractive surgery specialists, here to discuss some of the latest hot topics in ophthalmology.

Surgical management of glaucoma has advanced dramatically in recent years. Not only have the techniques become more effective, but new devices have made these procedures much more accessible to the general ophthalmologist.

This month, Carlos Buznego, MD, and Inder Paul Singh, MD, discuss their preferences for minimally invasive glaucoma surgery devices. We hope you enjoy the discussion.

Kenneth A. Beckman, MD, FACS

MIGS puts glaucoma in doctor’s control

We have three FDA-approved devices for combined cataract surgery with MIGS — Glaukos iStent, Glaukos iStent inject and Ivantis Hydrus — that have finally put glaucoma in the control of the doctor, and now we are faced with deciding when to apply each of them.

Carlos Buznego, MD
Carlos Buznego

Patients may be using medications that are expensive or difficult to administer, they may be borderline controlled, or compliance may be an issue. With MIGS, I can help get their glaucoma under control rather than just crossing my fingers that the patient is compliant.

The first step is identifying patient type, whether we will combine it with cataract surgery vs. a stand-alone procedure in a pseudophakic patient.

When I am doing combined surgery, I use trabecular micro-bypass stents. The iStent, iStent inject and Hydrus have all met the high bar that an FDA premarket application (PMA) trial requires, with randomized trials lasting several years. Adverse events are tracked and reported, and to me that is the level of evidence-based medicine that lets us know that it is a safe procedure. Some of the newer options with MIGS, such as goniotomy and canaloplasty, seem to be safe, but we do not have that same level of confidence we have with a PMA trial regarding the long-term and short-term complication rates.

In my hands, if you are having cataract surgery and have mild to moderate glaucoma, you are getting a micro-bypass stent. I have found the iStent inject to be a relatively straightforward procedure. We are getting good IOP control and a low complication rate. In this era of rising patient expectations of cataract surgery, a rapid “surprise-free” recovery is critical. Specifically, postop hyphemas are nearly nonexistent with the iStent inject, which compares favorably with goniotomy and canaloplasty.

Now let us consider the pseudophakic patient, which is a different group. Those three stents are not approved for pseudophakic patients, so for them I like to do some of the MIGS procedures such as goniotomy or canaloplasty or combining them. They have quick recovery times, are straightforward procedures, have a finite but low incidence of complications and give good results for lowering IOP.


The use of the Kahook Dual Blade (KDB, New World Medical) is the most straightforward, allowing us to do a successful excision rather than solely an incision of trabecular tissue. I like the guarded blade and call it “safety scissors for the trabecular meshwork.” We are able to get an incision without necessarily using a sharp-tipped instrument that could cause secondary issues, such as iris trauma or excessive bleeding. I think this is the best approach for the early to intermediate surgeon who is doing a MIGS procedure for the pseudophakic patient.

Next we have those with advanced, uncontrolled or refractory glaucoma, which might be somebody who is controlled on maximum medications but with advanced disease or advanced and/or controlled disease but the drainage system no longer works. Goniotomy or canaloplasty can sometimes be helpful, but often in these patients the conventional drainage system is no longer functional. In these cases we need to go back to traditional thought patterns of diverting aqueous out into the subconjunctival space.

In the Tube Versus Trabeculectomy Study, trabeculectomy and tube shunt surgery were found to have a high incidence of safety issues. The incidence of significant complications was 21% to 37%, while reoperations were required in 14% to 22%. Fortunately, newer devices that promise safer surgeries have been approved (Allergan’s Xen gel stent), and around the corner we expect FDA approval of the Santen MicroShunt.

Those two devices allow flow of aqueous from the anterior chamber, shunting into the subconjunctival space. However, rather than having a multistep procedure that requires multiple incision cautery suture technique like we have with tubes and trabs, we are able to do a relatively quick procedure that does not require manipulation in the anterior chamber and does not require viscoelastics or suturing, making it less traumatic, more expeditious and more repeatable. This is accomplished through either a stab incision from the anterior chamber out into the subconjunctival space (Xen internal approach) or puncture through the conjunctiva and the sclera into the anterior chamber (external approach for the Xen, standard approach for the MicroShunt).

For the refractory or more advanced patients, these new versions of MIGS, oftentimes called MIGS plus or MIGS plus bleb, are so much better than the traditional tube filtering surgery with less surgical trauma, more rapid operating times, rapid recovery time and lower complication rates.

Disclosure: Buznego reports he is a consultant for Allergan, on the speakers bureau for New World Medical, and a speaker for, consultant for and stockholder of Glaukos.


Comfort level helps guide procedure choice

We do not always know where the resistance to outflow is preoperatively, whether it is at the level of the trabecular meshwork, Schlemm’s canal or the distal channels, so that is why any one procedure may work better for someone. Therefore, the comfort level of the procedure, knowledge of previous surgery, number of medications and overall IOP help guide the surgeon.

Inder Paul Singh, MD
Inder Paul Singh

The Hydrus and iStent are FDA approved for use with concomitant cataract surgery, so if someone is pseudophakic or phakic, you will not likely be doing a stent procedure, at least not on label. Other procedures, such as viscodilation, KDB or trabeculotomy, and Xen, can be done as stand-alone or concomitant with cataract surgery on phakic or pseudophakic patients in any patient who has mild to moderate or even more advanced/severe glaucoma. Xen can also be done as a stand-alone procedure, but the label is for a refractory patient — this patient could still have a mild, moderate or severe diagnosis depending on the visual field defect. So, the indication can often guide the surgeon on the procedure choice, but it is also how we define “refractory” that could impact how early in the disease we perform some procedures, such as the Xen. Refractory does not necessarily assume advanced glaucoma. For instance, someone with a nasal arcuate defect on three medications who cannot remember to take them and has allergies to topical medications is technically refractory.

The stenting procedures are nice because they are the least disruptive to tissues in terms of bypassing the trabecular meshwork and potentially scaffolding the canal, instead of removing or cutting tissue, so there is the possibility of performing a selective laser trabeculoplasty or even another angle-based surgery in the future.

If the resistance is more in the entire canal and distal channels, these stenting procedures may not be enough, although the Hydrus does scaffold 3 clock hours of the canal, and the iStent does have bidirectional flow. A procedure that viscodilates, breaks herniations in the canal and ostia of the collector channels, as well as flushes the outflow system may be beneficial, such as the iTrack catheter (Ellex), Visco 360 (Sight Sciences) or Omni (Sight Sciences) devices. I often default to a stent in a patient with mild to moderate cataract because I can always come back to that patient and do a KDB, viscodilation or trabeculotomy procedure as a stand-alone.


The iStent is so small that you still have space to do other procedures. The Hydrus is a little larger and occupies more of the nasal angle, so you may need to go to the inferior or temporal part of the angle if you have to go back in. However, a benefit, again, of the Hydrus is that it scaffolds Schlemm’s canal. All of these products have their own nuances, but the indication is a big part of it.

A question often comes up with these stents: “Is phaco doing all the work?” We presented a study at the American Society of Cataract and Refractive Surgery meeting demonstrating that patients in the phaco-only group (with no iStent) had a maximum IOP reduction of 5.5 mm Hg to 5.8 mm Hg in three different baseline unmedicated baseline IOP groups (25 mm Hg or less, 25 mm Hg to 30 mm Hg, or greater than 30 mm Hg), meaning that no matter what your baseline pressure was, we could not reduce the IOP any more than 5.8 mm Hg. But in the iStent group, the higher the baseline pressure was, the more pressure reduction you got (6.8 mm Hg, 7.8 mm Hg and 9 mm Hg, respectively). It finally differentiates what iStent does vs. what phaco-only does. The iStent actually improved outflow facility and was consistent with other studies demonstrating the higher the baseline IOP, the more reduction in IOP you will see. Many of our patients come to the office with IOPs in the upper teens on prostaglandin analogues. We do not usually wash them out to see how much reduction we achieved, so it is often hard to appreciate the benefits until you see data like this.

If I have a younger patient without a cataract, a situation in which a stent is not indicated, I may not want to remove trabecular meshwork tissue because I want to save it for a stent later on. In this case I would often choose a viscodilating procedure or try SLT first.

SLT is a fantastic first-line treatment. It helps decrease the need for drops, and the LiGHT study revealed that, compared with first-line drops, you have a better chance of achieving target pressure and less progression to incisional surgery with SLT vs. drops. In addition, theoretically, it helps me understand where the resistance to outflow might be. When we look at a patient, we do not know where the resistance is. So we have to separate the disease severity (mild, moderate, severe) that is based upon visual field loss vs. resistance severity. You can have a preperimetric mild glaucoma patient with little field loss but have significant resistance severity, meaning they need about three or four drops and still have an IOP of 25 mm Hg — early glaucoma but high resistance severity.

SLT works primarily at the level of the pigmented trabecular meshwork. If you do not have a robust response, that could mean the resistance may be in Schlemm’s canal or distal channel. If a patient does well with SLT, I would be more comfortable doing a procedure that bypasses the trabecular meshwork when they have cataract surgery later on. In a phakic patient, if SLT does not initially provide a response, I will often perform a viscodilating procedure and try SLT again postoperatively. We have seen fantastic results after viscodilating procedures.


A KDB is an all-purpose type of procedure as well — you can still do it during cataract surgery — but you only have one opportunity to do a stent, which is why I like to combine cataract surgery with a stent. I have done a KDB after iStent or Hydrus. However, if you have a hard time with the angle, I have done a goniosynechialysis to remove some of the trabecular meshwork from the iris and then have done a KDB goniotomy.

I have also gone back and viscodilated or done a KDB goniotomy or trabeculotomy on patients who have already had a previous tube or trabeculectomy or a Xen; you can actually reopen a drainage system. It is not a cookie-cutter approach. All procedures are beneficial and have their place. You must look ahead and determine if a procedure you perform now will preserve your patient’s ability to have another procedure in 5 or 10 years. What do we do to give ourselves the best chance of giving the most options to these patients as they get worse in their disease process?

If I cannot get enough control with any of the MIGS devices or conventional outflow pathway devices, we always have subconjunctival bypass surgery with the Xen gel stent.

It is also important to tell patients that these options are safe and will give us the best chance to decrease the need for drops and control the glaucoma; however, it is not a cure or a guarantee that more surgery may not be necessary in the future.

In general, it comes down to not only what is the best for your patient, but what is best in your hands as a surgeon and what you feel the most comfortable performing.

Disclosure: Singh reports he is a consultant for Ellex, Glaukos, Ivantis, Santen, Sight Sciences and New World Medical.