MIGS encompasses a variety of microsurgeries that can be categorized by their mechanisms of action, which include enhancing flow through the trabecular meshwork, shunting aqueous humor to the subconjunctival space, and decreasing aqueous humor production.
While traditional glaucoma filtering surgeries such as trabeculectomies and tube shunts hold a larger risk of complications such as endophthalmitis, hypotony, bleb leaks, fibrosis, and bleb infections.
MIGS is also often performed in combination with cataract extraction, particularly if patients also have visually-significant cataracts requiring removal, and the IOP-reducing benefits of both surgeries may be additive.
Cataract and glaucoma surgery have been combined for decades but were historically reserved for patients with severe or uncontrolled glaucoma.
The advent of micro-invasive glaucoma surgery (MIGS) has created a paradigm shift and has allowed us to offer surgical intervention for enhanced pressure control and/or medication burden reduction.
The shift is principally due to the known efficacy of MIGS procedures and their excellent safety profile. MIGS are routinely coupled with cataract surgery and are increasingly being offered as stand-alone procedures to reduce IOP and/or medication burden — even in the earliest form of glaucoma.
For patients with both glaucoma and cataract, the question becomes are clinicians treating a cataract patient who happens to have glaucoma, or are clinicians treating a glaucoma patient who happens to have a cataract?
And when the two are present, should we always intervene and manage a glaucoma while addressing the cataract — if so, which procedure?
“The numerous options now available to surgeons means factors such as glaucoma severity, target IOP and the number of medications patients are taking allow us to individualize the care of each patient,” says Steve R. Sarkisian, Jr., MD, owner and founder of Oklahoma Eye Surgeons, in Oklahoma City.
But when should these options be considered?.
The status of the crystalline lens and/or a device’s “indications for use” can drive a surgeons decision on which MIGS device to use to address patients’ glaucoma.
The FDA has approved trabecular micro-bypass with implantable microstents for use only when combined with cataract surgery. Other procedures, such as goniotomy and canaloplasty, can be performed as stand-alone procedures (phakic or pseudophakic) or in combination with cataract surgery.
The diode micropulse laser can be performed in all settings (phakic/pseudophakic/combined), while endoscopic cyclophotocoagulation (ECP) requires an eye to be pseudophakic in order to obtain a view of and treat the ciliary processes.
The status of the lens also helps guide John P. Berdahl, MD, Vance Thompson Vision, Sioux Falls, S.D. He notes that for pseudophakic patients who are controlled on one or two medications, he might consider selective laser trabeculoplasty (SLT) if the disease is progressing before offering a standalone MIGS.
For phakic eyes he adds, “Even though the long-term consequences of glaucoma are more worrisome than the cataract, most of the time we’re not going in to do that MIGS procedure unless the cataract is present.”
Exceptions include patients who are progressing on their current therapy or cannot tolerate eyedrops. “But if I’m less concerned about IOPlowering effects and more about eliminating drops in someone with a high IOP, then I’m going more towards a MIGS approach.
If they have a lower IOP or need even more IOP lowering, then I have a tendency to go towards goniotomy,” he says. “Generally, an IOP under 25 mm Hg presents us with different options than if their pressure is over 25 mm Hg — that’s not an absolute cut-off,” he says.
If there is rapid visual field progression, the threshold is going to be lower and patients may need a two-stage procedure with a more conservative option, such as an angle procedure first; if the IOP is not at target, a micro-pulse laser or a subconjunctival procedure may also need to be done.
“MIGS certainly works better in patients that have higher IOPs, 18 or 19 mm Hg and above,” Dr. Berdahl says. “Those are the patients that get the best benefit from MIGS.” In a well-controlled patient that is tolerating their medications well, “we’re not talking about MIGS as a standalone.”
In addition to the lens status, Inder Paul Singh, MD, of Eye Centers of Racine & Kenosha, Wis., includes the health of the visual field and optic nerve on the list of factors he considers when deciding which MIGS procedure he will use.
However, he adds, “If someone comes into my office who needs cataract surgery, I’m going to put in a MIGS device, regardless,” he says. “I’m not concerned about today. It’s what’s going to happen 6 months, 1 year, 5 years from now that I’m concerned about and trying to keep them stable throughout a 24-hour period for 10, 20 or 30 years.
There’s a huge value to me in reducing the medication burden, even if it’s only by one drop.” Anecdotally, Dr. Singh’s clinic evaluated post-MIGS patients to determine how much time was saved on the clinic side with reduced callbacks and verifications and determined they saved about 5 minutes of tech time for each medication reduction.
Disease severity, visual field loss, medication burden and anatomic variables must be balanced with the patient’s visual needs and/or occupation when deciding on a surgical procedure, Dr. Sarkisian explains.
“It’s not a cookie-cutter scenario because there are so many potential combinations with those four pillars,” he says. “You evaluate all of them and develop a personalized approach.” Dr. Singh also infers where “the pathologic resistance to outflow” resides.
A new philosophy he has been preaching is to “stage people based on severity of disease and outflow resistance.” Disease severity comprises the damage incurred to the optic nerve and its associated vision loss and serves as a means to develop a target pressure; resistance severity comprises the pathology of the outflow system, be it the trabecular meshwork (TM), Schlemm’s canal or a distal channel, he notes.
“The reason why that’s important is because with MIGS, the devices work at different levels of the outflow system,” Dr. Singh says. Traditionally, the more advanced the disease, the greater the pathologic changes to the retinal nerve fiber layer and the structures of the conventional outflow system, which culminates into more advanced visual field loss.
For patients on multiple medications, Dr. Singh considers viscodilating procedures to “physically break the herniations and flush the distal channels out. You’re basically hedging your bets and allowing yourself the best chance to get people off medications.”
Like Dr. Singh, Dr. Sarkisian likes to enhance the conventional outflow system first, whether it bewith the OMNI surgical system (Sight Sciences) or the TrabEx (Microsurgical Technology) or the iTrack microcatheter (Nova Eye).
He uses “whatever method is most comfortable to remove or strip the TM, with or without viscodilation,” Dr. Sarkisian says.
Because of MIGS (and SLT), more invasive procedures (trabeculectomy, tube shunts, gel implants) have been relegated to third- or fourth- line options, Dr. Berdahl says. “Anything that’s transscleral is almost always used after attempting a MIGS procedure first,” he explains.
“The rationale is that transscleral procedures have significantly more morbidity. I believe that in general we should give a MIGS procedure a shot in an effort to avoid a transscleral procedure, knowing that if the MIGS procedure isn’t enough we’ve exhausted our safest options and we’re left with our only alternatives, which do have more morbidity.”
In cases where angle-based MIGS procedures may be insufficient, Dr. Sarkisian chooses less invasive filtering procedures.
“If the pressure is high, I prefer to start with the XEN [Allergan] because in my hands, I can get the pressure much lower.”
If the IOP starts to increase after a XEN and a medication addition fail to achieve target IOP, he refers to the XEN revision procedure as a “bleb enhancement” rather than a “needling,” and his rates of needling (about 10%) are much lower than what’s published, “not because I’m a better surgeon than other people, but because from the very beginning, I made sure that I was in the subconjunctival/ supra-tenon space.”
He also recommends using about 60 µg of mitomycin-C. Looking ahead, Dr. Sarkisian believes MIGS will be combined with sustained-release medications such as Durysta (bimatoprost SR, Allergan). “I envision doing cataract surgery with the iStent or the OMNI and/or ECP, combined with Durysta,” he says.
“It’s going to be a major game changer, and we’ll be able to fulfill the MIGS dream of being able to get people off medications in a more substantial and sustainable way.”
As more comprehensive ophthalmologists perform MIGS, glaucoma specialists are seeing patients “a bit later in the course of their disease,” Dr. Sarkisian says.
“I am very happy to see that, to know we’re able to postpone aggressive treatment and get away with less aggressive secondary treatments as well.” MIGS has changed the characteristics of the patients he sees, which is “a huge blessing.”
Simple changes to patient interactions — such as moving from asking if they take their medications daily to how often they miss their medications during the week — can yield more information about the whole patient and may alter patient care, notes Dr. Singh.
“The definition of ‘uncontrolled’ has changed,” he says. “My definition is no longer just about high pressures or worsening fields,” and now includes patient concerns about cost, side effects and forgetfulness. “Anything like that where I think they’re not going to be compliant” is now considered an “uncontrolled patient due to compliance issues,” he says. Dr. Berdahl agrees.
“Sometimes we forget that there’s a whole patient behind the eye and that patient has a life that they’re living, that comprises not only what they have to do every day but also what they can afford and what their comorbidities are.
First, I ask, what’s best for the eye. And then I zoom out and say, is what’s best for the eye also best for the human connected to it?” That includes the capability to instill the drops as well as the financial resources to afford the drops, he says.
If a patient specifically says they can’t afford a branded medication or asks for the generic version, “you’re fighting them to take medications, and those patients are going to be problematic,” Dr. Singh says.
The introduction and benefit of MIGS, therefore, “is not just IOP reduction,” he explains. “It’s also the potential medication reduction and reducing the burden of drops on patients.”
Even for patients with perfectly controlled pressure (mid-teens, right at target) with stable fields and optic nerves, Dr. Singh warns that digging a little deeper often yields a less rosy reality. For one thing, three medications may have been required to get the patient to that target.
“That patient may not be obvious or visually or verbally telling you that they’re really unhappy, but when you ask, ‘By the way, do you ever forget the drops?’ it’s not uncommon for the response to be, ‘Yes, a few times a week,’ or to say they skipped a refill because the cost was an issue or they skipped the drop because their eyes get red and irritated,” he says.
“Glaucoma is a chronic, long-term disease. There’s a huge value in reducing the medication burden, even if it’s only by one drop and even if that’s only for a couple of years,” Dr. Singh says, and that’s what MIGS bring to the table.