Glaucoma 360: Decision-making in surgical glaucoma

ICYMI: Thomas Samuelson, MD, of the Minnesota Eye Consultants in Bloomington and Minnetoka, Minnesota, shares the key highlights from his presentation "Stents, trabs, and tubes: Decision-making in surgical glaucoma," during the 2020 Glaucoma 360 annual meeting in San Francisco, California.

Technology advances rapidly, even in medicine, and numerous therapies for glaucoma have been introduced over the years. But despite the advent of new and effective tools, which can be enticing for surgeons because of their very newness, limitations and weaknesses accompany them, according to Thomas W. Samuelson, MD. Therefore, balancing safety and efficacy remains the name of the game.

“Over the decades we have overvalued surgical efficacy and significantly undervalued surgical safety,” said Samuelson, who is in private practice at Minnesota Eye Consultants and is an adjunct professor of ophthalmology at the University of Minnesota in Minneapolis.

He added that surgeons should do their best to avoid subjecting patients to procedures with the potential for disastrous or catastrophic outcomes unless the disease risk particularly warrants taking that chance.

Despite all the newer surgical options in glaucoma and the technical skill needed to master minimally invasive glaucoma surgery (MIGS) and traditional trabeculectomy, “wisdom and judgment in surgery are every bit as important as surgical dexterity,” said Samuelson.

Upsides and realizations

Samuelson pointed out the advantageous developments for patients that have emerged over the previous decade.

“We have safer, more individualized surgery; less paternalistic approaches; more patient-centered outcomes; and realistic drug regimens that expand the scope of our safer interventions,” he said. “We will soon have depot delivery and can use that to make some of the safer surgeries more widely applicable to a greater disease spectrum.”

According to Samuelson, ophthalmologists are reverting to paying attention to physiologic outflow, which had all but been abandoned.

They are also moving toward a renewed recognition that they can improve the function of Schlemm’s canal as evidenced by the LiGHT trial, the favorable effects of phacoemulsification on intraocular pressure (IOP), netarsudil (Rhopressa, Aerie Pharmaceuticals), nitric oxide-donating prostaglandins, and newer canal procedures. Each of these interventions, at least in part, improves physiological outflow.

Collectively, such improvements translate into reduced eyedrop therapy for older patients.

“We can also better manipulate the episcleral venous pressure, which may improve the efficacy of the canal-based surgeries, and when we have more aggressive target pressures, we bypass the canal and go through the sclera with the gel stent, trabeculectomy, or tube,” Samuelson explained. “In doing so, we are bypassing the episcleral venous pressure altogether. The good news is that the pressure is lowered, and the bad news is that pressure may be lowered too much, risking hypotony.”

Opting for surgery

The classic scenario is that surgery becomes the option when there is an unacceptable risk of glaucomatous progression despite medications and laser treatment.

“A current strategy is for surgeons to control patients as well as possible with medications and laser until a cataract develops and then utilize the opportunity to treat both with a phaco[emulsification] plus procedure, the “plus” portion being the surgeons’ favorite MIGS procedure. While there are exceptions, this has become the most common time to intervene surgically for glaucoma.

"The trend seems to be to try a few medications, then proceed to the safer surgeries,” Samuelson pointed out.

The 4 most common surgical choices include cataract surgery alone, cataract surgery plus canal-based surgery, transscleral surgery, or ciliary ablative surgery.

In Samuelson’s practice, he rarely performs only cataract surgery in a glaucoma patient, and his surgical choices have changed from performing mostly phacoemulsification trabeculectomy to phacoemulsification plus a canal-based surgery. He also does not perform much ciliary ablative surgery until later on in the disease.

Why might surgeons prefer canal devices for phacoemulsification? Samuelson said it is important to keep 2 concepts in mind.

“[The first is that] in mild to moderate glaucoma, the outflow system is not completely dysfunctional but only mild to moderately dysfunctional. The second is what happens to the IOP during cataract surgery without altering the canal,” he explained. “There is convincing, level 1 evidence that cataract surgery alone lowers IOP at least modestly for most patients with a cataract and glaucoma.”

There is a great deal of evidence from 5 MIGS studies that the control arm (phacoemulsification alone) did well. But the study arm did even better, with lower IOPs and fewer medications. However, cataract surgery alone decreased the IOP in the iStent inject trial (Glaukos; NCT01444040) by 5.4 mm Hg, and by 5.3 mm Hg in the Hydrus Microstent trial (Ivantis; NCT01539239). Thus, before altering the canal in any way, on average the surgeon has improved the patient’s pressure control.

This is important because performing only a cataract surgery may help avoid procedures that could be risky for patients.

“In mild to moderate disease with moderately good canal physiology, I prefer the less-is-more approach,” Samuelson explained. “Also, I subscribe to Murray Johnstone’s research and believe that the canal tissue is complex, dynamic, pulsatile, and 3-dimensional and not simply a hollow passive tube. Thus, I am cautious about disrupting the canal excessively.”

Samuelson said he prefers “a minimalist approach for mild to moderate disease.”

“That said, as we progress down the disease severity spectrum, [we should] start to favor the procedures that are more disruptive in the canal,” he said. “For example, GATT [gonioscopy-assisted transluminal trabeculotomy] is a terrific choice for a patient with more significant disease risk in whom we are trying to avoid the risk of bleb-forming procedures.”

For patients with mild disease, the important question to consider is which procedure is less likely to cause a longer-term fibrotic response in the canal that was working reasonably well, according to Samuelson.

“While there is definitely a role for both strategies, I believe that the stealth nature of the canal devices are more tissue friendly. [They are] less likely to cause a deleterious healing response [in the] longer term than procedures that are more ablative within the canal,” he noted.

To further explain this approach, he pointed out that one can augment the pressure-lowering benefits of the phacoemulsification procedure by injecting 2 iStents (dimension, <0.5 mm) into the canal. The entire canal has a circumference of approximately 36 millimeters; thus, with this approach, a surgeon leaves 98.7% of the canal undisrupted.

A prospective randomized clinical trial demonstrated the benefit of this, and it is easy to understand why the risk of longer-term harm due to fibrosis or adverse healing is negligible. Generally, Samuelson said he uses the iStent as his earliest intervention and the Hydrus Microstent at an intermediate time.

Incisional or ablative canal procedures he reserves as stand-alone options or for patients with significant disease, Samuelson noted.

“An important point for me is that we must remind ourselves that it is one thing to assume risk for ourselves, but subjecting others to risk is different,” Samuelson said. “We need to constantly ask, ‘What would I want for myself?’ Generally, we migrate to the procedure with lower risk.”

Associated with that philosophy is that while the safer surgeries lessen surgical risk, they may increase disease risk because the resultant IOPs may not be sufficiently low. Conversely, traditional surgeries are more effective, achieve lower IOPs, and reduce disease risk, but they increase the surgical risk, Samuelson concluded.

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