While MIGS has forever changed the surgical management of glaucoma, the space continues to evolve.
Decision-making in surgical glaucoma is a complex and individualized process because there are a variety of important factors to consider. “Deciding which procedure to perform takes into account some obvious issues, along with some that are more nuanced,” said Thomas W. Samuelson, MD, founding partner, Minnesota Eye Consultants, and adjunct associate professor of ophthalmology, University of Minnesota, Minneapolis.
Dr. Samuelson outlined his approach to glaucoma surgery at the 23rd annual Glaucoma Symposium, held during the 2019 Glaucoma 360 meeting.
“I always start with the guiding principle, however, that the risk of surgery should not exceed the risk of the disease,” Dr. Samuelson pointed out. “Fortunately, we now have the luxury of matching the two.”
Dr. Samuelson said glaucoma progression–its likelihood and expected rate–is his top concern when deciding on glaucoma surgery. Other “obvious” factors include status of the crystalline lens, refractive status, the patient’s general health, glaucoma severity, and how well the patient adheres to and is tolerating medical therapy.
The nuanced factors include coagulation and conjunctiva status, expected need for inflammation control with a topical corticosteroid, and axial length, which influences risk for adverse effects from hypotony.
Combining surgeries Dr. Samuelson said that because IOP can be controlled in many patients with mild-to-moderate glaucoma, he waits to do a minimally invasive glaucoma surgery (MIGS) procedure until cataract surgery becomes indicated.
When doing a combined procedure, Dr. Samuelson considers that by improving phys-iological outflow, based on the prospective randomized MIGS trials, cataract surgery alone has a well-documented benefit for lowering IOP by about 5.5 mm Hg from a baseline intraocular pressure (IOP) in the mid-20s mm Hg.
In eyes with mild-to-moderate disease in which the trabecular meshwork is “modestly dysfunctional,” he favors a canal procedure and chooses to either place two trabecular micro-bypass stents (iStent Inject, Glaukos) or the larger trabecular bypass stent (Hydrus, Ivantis). A canal-based MIGS procedure with one of the indwelling stents might also be an option for a patient with advanced disease, whose visual field has been stable for years and whose IOP is well-controlled on medication.
“These canal procedures are predictable,” said Dr. Samuelson. “Because they enhance physiological outflow, they act synergistically with cataract surgery. They are also minimally disruptive to normal anatomy.”
He added that there are data for both stent procedures showing an enduring benefit when they are combined with cataract surgery. The larger stent is a more disruptive, but also has a slightly greater effect on IOP.
The possibility that canal-based procedures, involving tissue incision or ablation (Omni Glaucoma Treatment System, Sight Sciences; Kahook Dual Blade, New World Medical; iTrack, Ellex; Trabectome, Ellex; and gonioscopy-assisted transluminal trabeculotomy), may lead to scarring (and harm outflow in the future) also weighs in favor of choosing one of the less intrusive stenting procedures for patients with mild disease.
“By doing cataract surgery with a ‘gentle’ MIGS procedure, I am not burning any bridges and can be more aggressive with surgical intervention later if needed,” Dr. Samuelson said.
Moving up the ladder The incisional/ablative canal surgeries may be strongly considered in eyes needing aggressive IOP-lowering. Transscleral procedures (Xen Gel Stent, Allergan; EX-PRESS, Alcon Laboratories; trabeculectomy; tubes) come with even greater potential benefit because they bypass physiological outflow, but they also carry greater risk.
Compared with traditional filtration surgery, the transscleral ab interno gel stent (XEN Gel Stent) allows for a standardized approach and greater intraoperative efficiency. It also requires less postoperative care and carries less risk of profound or sustained hypotony relative to trabeculectomy.
Unlike trabeculectomy, however, IOP is not titratable with the gel stent. Presenting a video from a gel stent case, Dr. Samuelson explained that passing the entire bevel of the needle through both sclera and Tenons avoids entanglement in Tenons and seems to have resulted in better outcomes. He also noted that some glau-coma surgeons have moved to the gel implant as an ab externo procedure.
“That is something I plan to try in the future,” Dr. Samuelson said. “That could allow the surgery to be done as an in-office procedure.”
Whereas MIGS has forever changed the surgical management of glaucoma, the space continues to evolve. There are no standardized approaches and glaucoma surgeons have their own preferred strategies for choosing a particular procedure for a particular patient, but those are subject to evolution.
“My current approach is just that–my approach at this time, because the changes with MIGS are happening so rapidly,” Dr. Samuelson said.