July 2017

 

COVER FEATURE

 

MIGS roundup
Tips and techniques for optimizing approved MIGS


by Michelle Stephenson EyeWorld Contributing Writer

   

Staining of the trabecular meshwork with trypan blue at the point of the incision in the meshwork. The opening in the meshwork exposes the white posterior wall of Schlemm’s canal. Note the “flaps” of the blue trabecular meshwork.
Source: Reay Brown, MD

Intraoperative view of an iStent in good position. The remainder of the stent is pointing to the left and is covered by the trabecular meshwork.
Source: Michael Greenwood, MD


 

Microinvasive glaucoma surgery (MIGS) lowers IOP with less tissue disruption than traditional glaucoma surgeries and has been found to effectively treat mild to moderate glaucoma

There are a lot of approved MIGS procedures all of a sudden, and these procedures fill a tremendous gap as we are trying to move toward safer procedures and earlier intervention,” said John Berdahl, MD, Sioux Falls, South Dakota. “The gap that used to exist between eye drops and a trabeculectomy or a tube shunt was enormous. This allows us to intervene earlier in the disease in a safer way.”
The currently approved procedures work in three different areas of the eye: the canal, the suprachoroidal space, and the subconjunctival space.
“The FDA labeling indications for the canal and suprachoroidal space procedures is in addition to cataract surgery for mild to moderate glaucoma,” said Richard Lewis, MD, Sacramento. “Over time, I think that will change, and I think we will find that these procedures are useful in pseudophakic and phakic eyes. However, this is currently off-label, so there are concerns about reimbursement.”

Canal-based procedures

According to Dr. Lewis, the canal- based procedures require an open angle. They include iStent (Glaukos, San Clemente, California), ABiC (ab interno canaloplasty, Ellex, Minneapolis), TRAB 360 (Sight Sciences, Menlo Park, California), gonioscopy-assisted transluminal trabeculotomy (GATT), and the Kahook Dual Blade (New World Medical, Rancho Cucamonga, California).
iStent is a trabecular micro-bypass implant. It was the first FDA-approved device for the treatment of mild to moderate open-angle glaucoma and the first MIGS implant to improve the eye’s natural fluid outflow by creating a permanent opening in the trabecular meshwork to lower IOP. It can be safely implanted in the eye during cataract surgery, and it spares important eye tissue that is often damaged by traditional surgeries. It can be implanted through a 1.5-mm corneal incision.
Instead of inserting a device into the eye, the Kahook Dual Blade has a pointed tip and two blades that excise the trabecular meshwork and remove it, which allows for aqueous flow from the anterior chamber into Schlemm’s canal, without having to go through the trabecular meshwork, which is thought to be the site of greatest resistance. “This procedure can be performed in any patient, regardless of whether they have a cataract or have previously had cataract surgery,” said Michael Greenwood, MD, Fargo, North Dakota. “It can also treat all severities of glaucoma, while the iStent is only approved for mild and moderate glaucoma.”
According to Dr. Greenwood, the Trabectome (NeoMedix, Tustin, California) is very similar to the Kahook Dual Blade, but it uses electrocautery to ablate the trabecular meshwork. “You do need extra equipment to do the Trabectome, whereas the Kahook Dual Blade does not require any additional equipment,” he added.
Another MIGS procedure is the TRAB 360. “It is a trabeculotome, which allows you to make a 180-degree incision in the trabecular meshwork. The surgeon makes one pass clockwise and one pass counterclockwise. This allows 360 degrees of cutting of the trabecular meshwork. Again, you don’t need any additional equipment except the device itself,” Dr. Greenwood noted.
ABiC is a new MIGS procedure that can comprehensively restore the natural outflow pathways in glaucoma patients. It is performed via a self-sealing, clear corneal incision, which preserves the clinically proven benefits of 360-degree viscodilation of Schlemm’s canal provided by traditional canaloplasty but has the speed and ease of a MIGS procedure. It has been shown to be effective alone or in combination with cataract surgery.
GATT is a MIGS procedure that effectively manages open-angle glaucoma. It is performed via microincisions in the cornea. A 1.0-mm incision is made in the periphery of the cornea through which the surgery is completed. After entering the eye, the surgical procedure involves cutting through the trabecular meshwork, cannulating Schlemm’s canal 360 degrees, and then unroofing Schlemm’s canal. One major advantage of the procedure is that it accesses the entire natural drainage system and opens it 360 degrees, rather than targeting only a small portion of the drainage system. Opening the whole drainage system provides adequate pressure lowering. Another advantage is that it does not involve opening conjunctival tissues to access Schlemm’s canal.

Suprachoroidal procedure

The CyPass Micro-Stent (Alcon, Fort Worth, Texas) is a supraciliary device designed to create a controlled outflow pathway to the suprachoroidal space. The device is a 6.35-mm long tube made of a polyimide material with an outer diameter of 0.51 mm. It can be placed through a 1.5-mm corneal incision and is inserted on a small guidewire with a special tip that separates the iris from the scleral spur. The CyPass Micro-Stent is inserted into the cleft that’s created, and the openings along the length of the tube allow aqueous to flow out.
“Instead of targeting the trabecular meshwork, CyPass goes into the suprachoroidal space, which can offer an alternative pathway for aqueous to flow,” Dr. Greenwood said. “It may be a viable alternative for patients with elevated episcleral venous pressure.”

Subconjunctival procedure

XEN45 Gel Stent (Allergan, Dublin, Ireland) is a stent made of a soft, collagen-derived gelatin. It is 6 mm long and is approximately the width of a human hair. The stent is injected through a small self-sealing corneal incision using a preloaded IOL-like injector. After being implanted in the eye, it creates a gentle outflow of aqueous from the anterior chamber into the subconjunctival space.
“XEN is a much safer intervention for people who might otherwise need a traditional tube surgery,” Dr. Greenwood said. “The data on both the CyPass and the XEN are early but good, so we are learning more as surgeons gain more experience with these devices.”

Why MIGS?

According to Dr. Berdahl, the ideal patient for a MIGS procedure is someone who needs a modest amount of IOP lowering. “Some procedures, like XEN, can get the pressure a little bit lower, but that comes with a trade for a little more risk and a little more postoperative care as opposed to an iStent, which can provide nice IOP lowering with a nice safety profile, but likely not down into the very low double digits. In general, it is a balance between efficacy and risk. The more IOP lowering you are looking for, the more risk is associated with it. A more modest IOP response comes with a lower amount of risk,” he explained.
Dr. Lewis agreed. “MIGS are much safer than traditional glaucoma surgeries and achieve reasonable pressure reduction with minimal risk. We are becoming comfortable with how and when to use them. I think all of them will ultimately be used with or without cataract surgery, and they will be used for a broader range of glaucoma. Now we are trying to figure out the right candidates for each treatment and how to best facilitate achieving optimum pressure control. It sounds a lot easier than it is. The bottom line is the way the wound heals.”
Although MIGS offers benefits compared to traditional glaucoma surgeries, there are still instances in which traditional surgeries are preferred. “If patients are not candidates for MIGS, I use a trabeculectomy approach. Additionally, the use of drainage devices is going to continue. However, MIGS will ultimately erode the numbers as we get more comfortable and begin to find ways to more effectively get pressure control. I am still doing traditional surgery, but it’s going to be interesting over the next 5 years as we adopt these new procedures, begin to achieve good pressure control with a much safer profile, and get full reimbursement,” Dr. Lewis said.

Tips for success with MIGS

According to Dr. Lewis, the key to success with MIGS is getting comfortable in the operating room with gonioscopy. “The big challenge for non-glaucoma surgeons is that they have to get comfortable using a gonioprism in their non-dominant hand without pushing too hard and getting the optimal view. It requires proper head position and maximizing the magnification. All of these fundamental tips are crucial to getting the best view. People who don’t take the time to get the best view are compromising their outcomes. Fundamentals are important even before you implant the device,” he said.
Before performing MIGS, Dr. Greenwood recommended getting comfortable with the anatomy of the angle. “We encourage surgeons to practice in the clinic and do gonioscopy so that they can get a good feel for the angle structures. Then start doing them on your routine cataract cases. At the end of the day, taking a couple of extra minutes to practice goniotomy on patients in the operating room can be helpful. Having a good view and being comfortable with the maneuvers that are needed to do these procedures is the most important aspect of surgery,” he said.
Reay Brown, MD, Atlanta, said that staining the trabecular meshwork with trypan blue has helped his technique. “The idea is to stain the meshwork the same way that you would stain the anterior capsule in a case where you have either a dark brown nucleus or a white nucleus,” he said. “The idea is to light up the trabecular meshwork by staining it with trypan blue. This is a big help because it shows you where the canal is and it reveals the posterior wall as you are implanting the iStent, so you know you are implanting it at the right depth. It identifies what you are aiming for, and it also gives you a positive sign that you have found the right channel.”

Who should perform MIGS?

According to Dr. Berdahl, there are three types of surgeons who consider incorporating MIGS in their practices, and they all have a different question. “Comprehensive ophthalmologists question whether they see enough of these patients to perfect their technique. Data indicate that 20% of patients undergoing cataract surgery have a concurrent diagnosis of glaucoma, so I think the answer there is yes. High-volume cataract surgeons question whether they want to get into the MIGS game, and I think that’s a fair question. If they don’t, I think that’s OK. However, even if you don’t offer MIGS as a high-volume cataract surgeon, if there is a patient with cataract and glaucoma, you should let him or her know that there is a good option out there. The third surgeon is the glaucoma specialist who questions whether MIGS can get the pressure low enough for the advanced glaucoma patients, and the answer is maybe. In general, it is a good place to start because it is so safe. If it doesn’t get the pressure low enough, you can move on to a more aggressive but riskier glaucoma surgery,” he explained.
Today, MIGS procedures are allowing surgeons to treat glaucoma earlier and more safely than traditional glaucoma procedures. “Surgeons are going to find their preferred MIGS surgery,” Dr. Greenwood said. “As time goes by and more data become available, we may learn that some are superior to others. Right now, surgeons have to understand what data are available and decide what they think is an equal balance of safety and efficacy for each individual patient.”

Editors’ note: Dr. Berdahl has financial interests with Glaukos, Alcon, Allergan, Johnson & Johnson Vision (Santa Ana, California), and New World Medical. Dr. Brown has financial interests with Glaukos. Dr. Lewis has financial interests with Allergan, Glaukos, Alcon, Ivantis (Irvine, California), and Aerie Pharmaceuticals (Irvine, California). Dr. Greenwood has no financial interests related to his comments.

Contact information

Berdahl
: john.berdahl@vancethompsonvision.com
Brown: reaymary@comcast.net
Greenwood: michael.greenwood@vancethompsonvision.com
Lewis: rlewiseyemd@yahoo.com

Tips and techniques for optimizing approved MIGS Tips and techniques for optimizing approved MIGS
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