July 2018


Device focus
MIGS for cataract surgeons

by Michelle Stephenson EyeWorld Contributing Writer

iStent Trabecular Micro-Bypass Stent
Source: Glaukos

Ab interno canaloplasty (ABiC) using the iTrack catheter
Source: Ellex

CyPass Micro-Stent Ultra System
Source: Alcon


MIGS for the novice
John Odette, MD, discusses the role MIGS is playing in
cataract practices.

Many new MIGS technologies have come to the market during the past decade. According to Constance Okeke, MD, Virginia Eye Consultants, Norfolk, Virginia, “One of the best ways to categorize the various technologies is by mechanism of action.”

Removal of trabecular meshwork

Several MIGS procedures involve the removal of trabecular meshwork, which is the area thought to be of highest outflow resistance. These include the Trabectome (NeoMedix, Tustin, California), TRAB 360 (Sight Sciences, Menlo Park, California), the Kahook Dual Blade (New World Medical, Rancho Cucamonga, California), and gonioscopy-assisted transluminal trabeculotomy (GATT). “All of these devices or procedures remove either a portion of or up to 360 degrees of trabecular meshwork tissue,” Dr. Okeke said. “The TRAB 360, the Kahook Dual Blade, and GATT are procedures that can be done with a disposable device, whereas the Trabectome comes with a whole electrical system for removal with fluidics. These trabecular meshwork removal procedures can be done in combination with cataract surgery or stand alone.”

Bypass of the trabecular meshwork

The iStent (Glaukos, San Clemente, California) bypasses the trabecular meshwork, and this is FDA approved to be performed in conjunction with cataract surgery. “By bypassing the trabecular meshwork tissue, one is able to create a conduit that directly allows fluid to enter Schlemm’s canal,” Dr. Okeke explained. “A single iStent is currently available. We’re hoping to soon have access to the iStent Inject, which is a more intuitive design and offers placement of two stents at one time.”

Dilation of Schlemm’s canal

Canaloplasty lowers pressure by dilating Schlemm’s canal to restore natural outflow. “Two devices have this mechanism of action: Visco360 by Sight Science and ab interno canaloplasty (ABiC), which uses the illuminated iTrack catheter by Ellex [Adelaide, Australia],” Dr. Okeke said. “Both devices allow for a catheter to be inserted into Schlemm’s canal, which allows for the placement of viscoelastic that can dilate Schlemm’s canal and open up any areas of adhesions and stretch open the distal collector channels.”

Shunting to the suprachoroidal space

This is one of the newer mechanisms of action, and it is FDA approved to be performed only in conjunction with cataract surgery. The CyPass Micro-Stent (Alcon, Fort Worth, Texas) is a microstent that allows the surgeon to have access from the anterior chamber to the supraciliary space to allow for flow to that area. “The Glaukos iStent Supra is coming down the pipeline. It is not yet available, but it also accesses the supraciliary space,” Dr. Okeke said. “The term supraciliary space versus suprachoroidal space are seen as one and the same.”

Shunting to the subconjunctival space

This is done with the XEN Gel Stent (Allergan, Dublin, Ireland), which allows fluid to flow from the anterior chamber through to the subconjunctival space.
“Soon to come down the pipeline is the Hydrus Microstent by Ivantis [Irvine, California],” Dr. Okeke added.

Candidates for MIGS procedures

Dr. Okeke said it is important to set realistic patient expectations to achieve a good outcome. “When thinking about who is a good candidate, success should be achieving a 20–30% pressure reduction or a pressure that is in the mid-teens. Success in many of the MIGS studies was defined as an eye pressure reduction of 20% or more from baseline, so that should also be considered success in the real world setting. Typically, patients are able to get off at least one medication,” she explained.
According to Dan Bettis, MD, University of Iowa, Iowa City, ideal patients for MIGS are those with mild to moderate open angle glaucoma. They should be relatively well controlled on medication. “We know from Medicare data that this includes 15–20% of patients undergoing cataract surgery in the United States,” he said. “This represents an opportunity for the cataract surgeon to offer additional value to his or her patients by helping them better manage their glaucoma. Given the improved safety profile and more rapid visual recovery, MIGS can also be considered in patients for whom traditional glaucoma surgery is deemed relatively high risk. Though early studies show MIGS may be less effective in lowering IOP than traditional glaucoma surgeries, MIGS fills an important gap in the treatment of patients who would benefit from lower IOP but do not warrant the risk of traditional surgery.”
Dr. Okeke agreed that the angle should be open. “Ideally, that angle should be nice and open, with no other pathology. Patients should have good nerve reserve, meaning that their optic nerve cup-to-disc ratio should be at least 0.75 or better. You want to have some level of reserve of nerve tissue so that in case the patient is in need of more pressure-lowering or you need to go to another surgical procedure, you’re not dealing with the last bit of fragile optic nerve tissue that’s available. Patients should ideally be in the early to moderate stage. MIGS procedures can be performed in patients who are moderate to advanced, but most MIGS procedures are looking at good success with early to moderate stage glaucoma,” Dr. Okeke said.
She added that the XEN Gel Stent is indicated for patients who are in the more moderate to advanced stages of glaucoma.
Poor MIGS candidates are those who have severe open angle glaucoma on maximum medical therapy. Patients with poor angle anatomy such as synechial angle closure, neovascularization, congenital anomalies, or severe corneal opacity so that the angle can’t be seen are also not good candidates. “If you can’t see the angle, you can’t treat it,” Dr. Okeke said.

Getting started with MIGS

According to Rick Lewis, MD, Sacramento, California, many cataract surgeons haven’t yet been trained to use some of the newer approaches. “They are sticking with what they are comfortable with. The CyPass and the XEN are relatively new, and some of the other approaches are just coming out, so they haven’t been trained, but over time, I think there will be more utilization of all of these other procedures,” he noted.
For cataract surgeons who have not yet performed MIGS, Dr. Okeke recommended getting started with gonioscopy. “They need to get comfortable with gonioscopy to perform the MIGS procedure, to be able to look for ideal candidates, and to be able to monitor MIGS patients after the procedure is done. It’s all about the angle, and the more comfortable you are with the angle, the more you’ll be able to easily adopt a MIGS procedure. In the operating room, you can use a Swan Jacob goniolens. If you don’t have one, you should order one even before you start to do any MIGS procedures. Start practicing the foundational steps of tilting the microscope toward you, tilting the patient’s head away from you, and using your non-dominant hand to hold the goniolens on the cornea. The next step would be to do that plus introduce another instrument in the eye and have the two hands working together,” she added.
Dr. Lewis agreed. “Before they do the procedure, I think they should get comfortable using a gonioprism in the operating room at the end of cataract surgery with the eye still full of viscoelastic. In other words, they’ve taken the cataract out, put the new lens in, and the eye still has viscoelastic in it. Then, you can get a gonioprism and use a Sinskey hook to identify the angle and the angle structures. The biggest problem is that most new surgeons don’t get good visualization. They’re not comfortable, so they must reposition the head and the microscope. They don’t do it enough; therefore, the visualization they get of the angle is poor. Then they are struggling because they’re not seeing it well,” he explained.
Just like using more than one medication to control glaucoma, some surgeons employ more than one MIGS technique. “Sometimes procedures might have an additive effect, and sometimes they may be used in succession,” Dr. Okeke said. “There is the opportunity to do MIGS after MIGS and still get good outcomes and extend the life of the eye. I think that the more MIGS procedures with various mechanisms of action that you can have under your belt, the better able you are to serve your patients and individualize their care.”
Dr. Bettis said that cataract surgeons who are just starting out with MIGS may want to stick to one modality until they get comfortable. “This will allow them to more quickly gain momentum and experience. Once they are comfortable and can see the net value added to their patients, I think they will want to explore additional MIGS modalities. This allows for an individualized treatment plan and titration of the risk and reward to a level that is appropriate. The approach for a patient with mild glaucoma on one medicine is likely different from the patient who is struggling to get in three different medications per day. For the latter patient, I would be more likely to target a larger proportion of the angle or either the suprachoroidal or subconjunctival space,” he said.

Editors’ note: Dr. Lewis has financial interests with Aerie Pharmaceuticals (Durham, North Carolina), Allergan, Advanced Vision Science (Goleta, California), Alcon, Ivantis, New World Medical, MicroOptx (Maple Grove, Minnesota), and Sight Sciences. Dr. Okeke has financial interests with Aerie Pharmaceuticals, Allergan, Alcon, Ellex, Glaukos, NeoMedix, Novartis (Basel, Switzerland), and Bausch + Lomb (Bridgewater, New Jersey). Dr. Bettis has no financial interests related to his comments.

Contact information

: dabettis@gmail.com
Lewis: rlewiseyemd@yahoo.com
Okeke: iglaucoma@gmail.com

MIGS for cataract surgeons MIGS for cataract surgeons
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