Over the past two decades, glaucoma surgery has changed substantially. Traditional operations such as trabeculectomy and glaucoma drainage implants remain important treatments, particularly when a large reduction in eye pressure is needed. At the same time, a group of less invasive procedures known as minimally invasive glaucoma surgery, or MIGS, has expanded the surgical options available for selected patients with glaucoma.
What Is MIGS?
MIGS is an umbrella term rather than a single operation. It generally refers to glaucoma procedures designed to lower intraocular pressure while causing less disruption to the eye than traditional glaucoma surgery. Many MIGS procedures work by improving the eye's existing drainage pathways, while others create a new route for fluid to leave the eye.
The overall goal is to find a balance between pressure lowering and surgical risk. In general, MIGS procedures tend to have a more favorable recovery and safety profile than traditional filtering surgery, but they also usually produce a more modest reduction in eye pressure. For this reason, MIGS should not be viewed as a replacement for every traditional glaucoma operation.
A Brief History of MIGS
The idea of improving the eye's natural drainage system is not new. Surgeons experimented with procedures involving the trabecular meshwork and Schlemm's canal long before the term MIGS became common. What changed in the 2000s and 2010s was the development of smaller implants, specialized instruments, and surgical techniques that allowed these procedures to be performed through very small corneal incisions.
The term MIGS gradually came to describe a growing family of procedures that attempted to lower pressure with less tissue disruption than trabeculectomy or tube-shunt surgery. Since then, the category has expanded to include several different approaches, including microscopic implants, removal or opening of part of the eye's natural drainage tissue such as goniotomy, and procedures that enhance drainage through Schlemm's canal such as canaloplasty.
The First FDA-Approved MIGS Implant: iStent
A major milestone occurred in 2012, when the U.S. Food and Drug Administration approved the original iStent Trabecular Micro-Bypass Stent for use together with cataract surgery in certain adults with mild-to-moderate open-angle glaucoma. It is widely regarded as the first FDA-approved MIGS implant in the United States.
The original iStent is a very small implant placed through the trabecular meshwork, the tissue through which fluid normally exits the front of the eye. The stent provides a small bypass into Schlemm's canal, allowing fluid to reach the eye's natural drainage system more directly.
Randomized studies of the original device showed that adding an iStent to cataract surgery could improve pressure control and reduce the need for glaucoma medication in some patients compared with cataract surgery alone. As with many glaucoma procedures, however, the amount of pressure reduction varies among patients.
How the iStent Has Evolved
The iStent platform has gone through several generations. The changes have generally focused on making implantation easier and allowing treatment of more than one area of the eye's drainage system.
Original iStent: The first-generation device consisted of a single microscopic stent and was approved in the United States in 2012 for implantation at the time of cataract surgery in appropriately selected patients.
iStent inject: The next major generation used a preloaded injector designed to place two smaller stents into the trabecular meshwork. The FDA approved iStent inject in 2018 for use with cataract surgery in adults with mild-to-moderate primary open-angle glaucoma.
iStent inject W: This later version retained the two-stent approach while modifying the stent design and delivery system. Its purpose remained the same: to create small bypasses through the trabecular meshwork into Schlemm's canal.
iStent infinite: Cleared by the FDA in 2022, iStent infinite is preloaded with three stents and differs importantly from the earlier U.S. iStent indications because it can be used as a standalone glaucoma procedure rather than only at the time of cataract surgery. Its FDA-cleared indication is specifically for adult patients with primary open-angle glaucoma that remains uncontrolled despite prior medical and surgical therapy; it should not be interpreted as a general standalone indication for every patient with glaucoma.
What Does the Evidence Show?
Published clinical trials support the ability of trabecular micro-bypass stents to lower intraocular pressure and, in some patients, reduce the number of glaucoma medications required. The evidence is strongest for the specific patient populations and surgical settings studied in those trials.
An important limitation is that MIGS is a broad category and the results of one procedure should not automatically be applied to another. Some MIGS procedures have several years of follow-up, but the amount and quality of long-term evidence varies by device and procedure. Studies sponsored by device manufacturers have also contributed substantially to the evidence base. Independent studies and longer-term comparative data remain important for determining how durable these procedures are and how they compare with medications, laser treatment, other MIGS procedures, and traditional glaucoma surgery over many years.
Where MIGS Fits in Glaucoma Treatment
MIGS has expanded the range of surgical options between medication or laser treatment and more invasive glaucoma surgery. In appropriately selected patients, a MIGS procedure may reduce eye pressure, reduce dependence on glaucoma drops, or both. The expected pressure reduction, however, is generally less dramatic than that achieved with procedures such as trabeculectomy or glaucoma drainage implants.
This distinction is particularly important in advanced glaucoma, where the target eye pressure may be very low. The choice of treatment depends on the type and severity of glaucoma, current pressure, rate of disease progression, medication burden, prior surgery, anatomy of the eye, and the pressure level that the treating ophthalmologist believes is necessary to protect vision.
Looking Ahead
MIGS represents an important change in the way glaucoma surgery is approached. Rather than relying only on medications until a patient requires traditional filtering surgery, ophthalmologists now have a wider range of surgical options with different balances of effectiveness and risk.
The field continues to evolve. New devices and techniques are being studied, and existing procedures are accumulating longer follow-up. For patients, the most useful way to think about MIGS is not as one operation or as a universally preferable form of glaucoma surgery, but as a growing group of procedures that may be appropriate in specific clinical situations. Continued independent research and long-term follow-up will be important for defining which procedures provide durable benefit and which patients are most likely to benefit.
Educational note: This article is intended for general educational purposes and does not provide individual medical advice. Treatment decisions should be made with an ophthalmologist familiar with the patient's glaucoma and overall eye health.
Works Cited
- U.S. Food and Drug Administration. iStent Trabecular Micro-Bypass Stent, Premarket Approval P080030. 2012.
- Samuelson TW, Katz LJ, Wells JM, Duh YJ, Giamporcaro JE; US iStent Study Group. Randomized evaluation of the trabecular micro-bypass stent with phacoemulsification in patients with glaucoma and cataract. Ophthalmology. 2011;118(3):459-467.
- Saheb H, Ahmed IIK. Micro-invasive glaucoma surgery: current perspectives and future directions. Current Opinion in Ophthalmology. 2012;23(2):96-104.
- Richter GM, Coleman AL. Minimally invasive glaucoma surgery: current status and future prospects. Clinical Ophthalmology. 2016;10:189-206.
- U.S. Food and Drug Administration. iStent inject Trabecular Micro-Bypass System. Premarket Approval P170043. Decision date June 21, 2018.
- U.S. Food and Drug Administration. Summary of Safety and Effectiveness Data: iStent inject Trabecular Micro-Bypass System. P170043. 2018.
- U.S. Food and Drug Administration. iStent inject W Trabecular Micro-Bypass System. PMA supplement P170043/S010. 2021.
- U.S. Food and Drug Administration. iStent infinite Trabecular Micro-Bypass System, Model iS3. 510(k) K220032. Decision date August 2, 2022.
- U.S. Food and Drug Administration. 510(k) Summary: iStent infinite Trabecular Micro-Bypass System Model iS3. K220032. 2022.
- American Academy of Ophthalmology. Preferred Practice Pattern: Primary Open-Angle Glaucoma. Current edition.