Surgeon expects more MIGS, less trabeculectomy.
Reviewed by Ang Li, MD
The type and number of glaucoma surgeries have changed markedly in recent years due to a variety of factors, said Ang Li, MD, an ophthalmologist at Cleveland Clinic Cole Eye Institute, in Ohio, at the Cleveland Eye Bank’s Vision Research Symposium on February 28.
Trabeculectomy and tube shunt procedures—the traditional glaucoma surgeries—create a reservoir (or bleb) for increased fluid flow and are associated with greater risk of tissue trauma, dissection, and complications. Newer, minimally invasive glaucoma surgeries (MIGS) do not form blebs but instead decrease fluid production or increase fluid outflow via natural pathways in the eye.
Present-day trabeculectomy entails the creation of a partial scleral flap to guard a full-thickness entryway into the eye that facilitates fluid flow via a steady trickle, which can be controlled as needed by adjustable sutures. “These characteristics…make…[it] the only modifiable and titratable glaucoma surgery. Trabeculectomy is also the most powerful glaucoma surgery…available to lower the intraocular pressure [IOP],” Li explained.
But despite being the gold standard, she pointed out, trabeculectomy is associated with complications like wound instability, maculopathy, choroidal effusion, lifelong risk of infection, and IOP lowering to the point of hypotony that leads to shallow or flat anterior chamber. These problems can affect vision more than the underlying glaucoma. And the bleb itself can become cystic and elevated, causing dry eye and severe discomfort. “This is what keeps glaucoma surgeons up at night.”
These devices were rapidly accepted by the surgical community because they were considered to be more controlled and safer than trabeculectomy, even though they may not offer as great a pressure-lowering effect.
Trabeculectomy-related complications led to the introduction of various glaucoma drainage devices, such as the Baerveldt implant (J & J Vision) and the Ahmed tube shunt (New World Medical), in the 1990s.
At the same time, laser treatments like the endoscopic cyclophotocoagulation that controls inflow in the eye were being refined. Selective laser trabeculoplasty followed argon laser trabeculoplasty and caused less tissue destruction and fewer complications. Aqueous suppressants and prostaglandins were also introduced in eye-drop form, and “overall, there was a burgeoning of laser, medical, and surgical treatments…during the 1990s that were responses to the pressure for change,” Li said.
According to Li, Medicare data from 1994 to 2012 showed a steady annual decrease in trabeculectomy, from about 50,000 procedures to below 20,000. At the same time, the use of tube shunts increased from 2000 to more than 12,000 per year. Cole Eye Institute data for 2011 indicates that tube shunt procedures began to plateau that year and trabeculectomy continued to decrease to about 50, which is below the number of tube shunt procedures performed.
The advent of MIGS in 2012 seemed to be the cause of declines in other surgical options. The iStent (Glaukos), introduced in 2012, quickly gained acceptance, followed by the Kahook Dual Blade (New World Medical) in 2015, the CyPass Micro-Stent (Alcon) in 2016 (later pulled from the market), the Xen Gel Stent (Allergan) in 2017, the Hydrus Microstent (Alcon) in 2018, and the OMNI Surgical System (Sight Sciences) in 2019. These MIGS devices, Li noted, increase outflow through the trabecular meshwork by bypassing the area of resistance through an implant or excision or by injection of a viscoelastic.
“The take-away message is that the number of trabeculectomy procedures performed has dropped dramatically due to the availability of tube shunt procedures and, more recently, by the introduction of MIGS,” Li concluded. “The trabeculectomy procedures…being performed are reserved for patients with severe glaucoma that demands IOPs in the single digits. The increased number of MIGS procedures is the result of earlier treatment of glaucoma, the ability to treat a wider age range of patients, and combining MIGS procedures with cataract procedures.”
Ang Li, MD
Li has no financial interest in this subject matter.