Surgeons are performing more minimally invasive glaucoma surgeries and fewer trabeculectomy procedures.
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.
Trabeculectomy and tube shunts
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],” explained Dr Ang Li, a glaucoma faculty member at the Cole Eye Institute of Cleveland Clinic, Ohio, US.
Despite being the gold standard, she noted, 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. The bleb itself can become cystic and elevated, causing dry eye and severe discomfort.
“This is what keeps glaucoma surgeons up at night,” Dr Li said.
Tube shunt devices were rapidly accepted by the 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 (Johnson & Johnson 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,” Dr Li said.
According to Dr 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.
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, Dr Li said, increase outflow through the trabecular meshwork by bypassing the area of resistance through an implant or excision or by injection of a viscoelastic.
“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,” Dr Li said.