MIGS: Expanding realm of glaucoma

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Microinvasive glaucoma surgery creates a new paradigm for the role of glaucoma surgery and is within the skillset of cataract and cornea surgeons.

By Cheryl Guttman Krader; Reviewed by Reay H. Brown, MD

Atlanta-Cataract surgeons and cornea specialists have been important in the development of microinvasive glaucoma surgery (MIGS), and they have an important role to play in its future, according to Reay H. Brown, MD.

“When the first MIGS device was approved, the question arose of whether it should only be implanted by glaucoma specialists,” said Dr. Brown, in private practice, Atlanta Ophthalmology Associates. “However, that was a debate that never got off the ground.”

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Cataract and cornea surgeons should care about MIGS because it is within their skillset and offers a chance for them to safely help glaucoma patients who need cataract surgery but not a trabeculectomy or tube surgery. Moreover, cataract and cornea surgeons have an amazing record of innovation, and glaucoma needs your innovative spirit, he noted.

Speaking about combined MIGS and cataract surgery, Dr. Brown explained that by strict definition, MIGS is performed through an ab interno incision and is not destructive or ablative. Based on its safety and efficacy, MIGS creates a new paradigm for the role of surgery in glaucoma management.

“MIGS introduces a new way of thinking about glaucoma surgery,” he said. “In the past, surgical intervention was considered for the 5% of patients who were on 4 or more medications. However, with MIGS, surgery is no longer a last resort for candidates failing maximal medical treatment with an elevated IOP and visual field progression.

“In fact, MIGS devices work best in the 95% of glaucoma patients who are 1 to 3 medications, and it offers them a way to lower IOP and reduce medication use along with the associated burdens of medication,” Dr. Brown said.

Nevertheless, he suggested surgeons who are just beginning to perform MIGS should pick patients undergoing cataract surgery who are on 1 or 2 IOP-lowering medications. These individuals account for more than three-fourths of patients with glaucoma. Other selection criteria include mild to moderate glaucoma and IOP that is relatively well controlled.

“When surgeons have more experience, they might consider MIGS for patients on 3 medications as long as the patient still has minimal visual field loss and the IOP is not too elevated,” he said. “Remember that MIGS is not a replacement for trabeculectomy and tubes, and so avoid patients with high IOP and advanced visual field loss.”

Recognizing who is an appropriate candidate for MIGS relates to understanding its outcomes. MIGS can reduce IOP to the mid to upper teens and/or lower medication use, but the amount of IOP lowering that can be achieved depends on the existing level.

“It is harder to reduce IOP if it is already controlled,” Dr. Brown said.

He illustrated his point by presenting results from the first 85 patients he implanted with the microbypass trabecular stent (iStent, Glaukos). Preoperative IOPs for the group ranged from <15 to >21 mm Hg.

However, when patients were divided into 4 groups based on their preoperative IOP, those with the highest IOP (>21 mm Hg) achieved a mean reduction of almost 6 mm Hg, while IOP fell by 3.2 mm Hg among those whose preoperative IOP was 19 to 21 mm Hg, but by only 1 mm Hg for patients with preoperative IOP 15 to 18 mm Hg, and 0.5 mm Hg in those with an even lower IOP.

“Overall, 96.5% if patients whose preoperative IOP was 18 mm Hg or above had a lower IOP after surgery,” Dr. Brown said.

Knowing the outcomes of MIGS also lets surgeons set proper expectations for patients.

“The goal of MIGS is to lower IOP and it may be possible to reduce the number of medications in patients with minimal visual field loss. But do not overpromise,” Dr. Brown said.

He also reminded surgeons that they have a parachute with MIGS.

“If the IOP gets too high, you can send the patient to the glaucoma specialist,” he said.

Reiterating that MIGS is within the skillset of anyone who is already doing cataract surgery, Dr. Brown noted that surgeons still need to educate themselves and be prepared to face a learning curve. Company-sponsored training for the iStent is available through Glaukos, and surgeons can supplement that by reviewing videos and obtaining a nonsterile device to practice delivery outside actual surgery.

“Expect some challenges,” he said. “You are going to be using new technology and should take advantage of the resources that are available to learn the technique.”

Dr. Brown added that gonioscopy is the most important skill to learn, and he suggested surgeons should practice getting the best gonio view possible on routine cases by turning the head and microscope.

Dr. Brown concluded by noting MIGS is just at its beginning. Although the iStent is the only FDA-approved MIGS procedure, and it is only approved for placement of a single device, other options are on the horizon. They include insertion of two micro-bypass trabecular stents (iStent inject; Glaukos), suprachoroidal stents for improving uveoscleral outflow (iStent Supra, Glaukos; CyPass Micro-Stent, Transcend Medical) and a flexible scaffold for permanently dilating and supporting Schlemm’s canal (Hydrus, Ivantis).

In addition, combination approaches are being explored that use two devices targeting different outflow pathways.

Reay H. Brown, MD

E: reaymary@comcast.net

This article was adapted from Dr. Brown’s presentation at Cornea Subspecialty Day during the 2014 meeting of the American Academy of Ophthalmology. Dr. Brown is a consultant to Ivantis and Transcend and has a financial interest in Glaukos.