University of California, San Francisco, UCSF Medical Center
One of the new and exciting prospects in the treatment of glaucoma is called MIGS, or Minimally Invasive Glaucoma Surgeries. These procedures are exciting from a patient’s perspective because they are generally safer with quicker recovery times.
Before discussing specific MIGS procedures, it would be helpful to define what constitutes “MIGS.” There are quite a few definitions of MIGS, but the American Glaucoma Society, which is the largest society of glaucoma specialists in the United States, provides the following working definition:
In meeting these criteria, MIGS procedures do not preclude the possibility of future, more traditional surgical approaches, such as trabeculectomy or tube shunt surgery.
There have been a plethora of abstracts, presentations, and papers in recent years detailing the use of MIGS procedures. However, there is still a lack of absolute consensus, even among clinical trials, as to what constitutes a MIGS device, which patients are most appropriately suited for these procedures, which MIGS device is the best to use in any particular patient, and what constitutes surgical success. The purpose of this article is not to provide an exhaustive or comprehensive list and details about all of the FDA approved and not yet approved MIGS procedures that are under development, but to give patients an overview of the MIGS procedures and some questions you will want to ask your ophthalmologist to find out if a MIGS procedure is right for you.
Narrator: Glaucoma: A group of diseases that damage the optic nerve is often caused by increased pressure in the eye, called intra-ocular pressure or IOP. Increased IOP is usually due to blocked drainage in the eye. If left untreated glaucoma can lead to severe vision loss and blindness. Fortunately, there are treatments available to slow the progression of glaucoma, including minimally invasive glaucoma surgery, called MIGS.
MIGS uses microscopic devices and tiny incisions to reduce IOP and slow the progression of glaucoma. MIGS may allow glaucoma patients to reduce their dependence on eyedrops.
One type of MIGS is a micro-stent. Micro-Stents help lower internal I pressure by increasing the outflow of fluid. These tiny implants or inserted at the edge of the iris and allow them fluid to access the drainage channel or bypass a blocked channel. Micro-stents or usually inserted during cataract surgery and remain in the eye permanently after the surgery. Your eye maybe slightly red and swollen and pressure may increase temporarily. Your vision may also be blurry for a few weeks after surgery but you can use your eyes normally.
You may be given eye drops to prevent infection and reduce swelling. If you feel unusual discomfort. Contact your doctor immediately. Talk with us today to learn whether MIGS is an option for you or someone you know with glaucoma.
Overall, MIGS procedures have been touted as safer than our traditional trabeculectomy or tube shunt surgeries. This is because they do not have some of the associated complications (or have less risk) from trabeculectomy and tube shunt procedures, such as too low eye pressure (hypotony) and bleb infection. However, doctors do not yet have long-term safety or effectiveness data. Currently, there are also no completed randomized clinical trials comparing MIGS procedures to the “gold standard” procedure of trabeculectomy.
Many of the MIGS procedures involve implantation of small devices. MIGS procedures are generally faster than trabeculectomy and tube shunt surgeries, and shortened surgical time can be very important for the safety of the patient. Most MIGS procedures are combined with cataract surgery, adding a short amount of time to the total surgical procedure. This is an important point to understand as well, since many clinical trials will compare a MIGS procedure combined with cataract surgery to cataract surgery alone. And indeed, cataract surgery alone has been shown to lower eye pressure to a small degree.
Lastly, an important point is that although the majority of MIGS procedures are safer than trabeculectomy, they are also not as effective in lowering eye pressure. The eye pressure in the majority of MIGS clinical trials is typically in the mid-teens range (approximately 15 mmHg). Many ophthalmologists do not think MIGS procedures are appropriate for patients who have advanced glaucoma and need much lower eye pressures.
To start off a discussion of some of the currently FDA approved MIGS procedures, the Trabectome (also called trabeculectomy ab-interno) will be described, which was FDA approved in 2006. The Trabectome is an electrocautery device that removes part of the trabecular meshwork, exposing the outflow channels of the eye and thereby lowering eye pressure. The trabecular meshwork constitutes part of the drainage system of the eye, and typically the drainage of fluid is impaired in glaucoma patients, causing eye pressure to increase. The Trabectome procedure is quick and can be combined with cataract surgery. The safety profile is quite good, with the most common complication being some blood in the front of the eye after the procedure. This complication is typically limited and clears fairly quickly; however, scarring can occur over the treated area, thereby limiting the effectiveness of the Trabectome method. Furthermore, as with most MIGS procedures, the eye pressure lowering effect is limited to the mid-teens.
Another procedure that is similar to Trabectome but uses a surgical instrument (no electrocautery) to remove a strip of the trabecular meshwork. The name of the surgical instrument is called Kahook Dual Blade (KDB). An exhaustive review of all MIGS procedures is outside the scope of this article, but I bring up the example of the KDB because there are many different ways developed or still being developed to remove diseased trabecular meshwork tissue and improve outflow.
More recently, the FDA has approved the use of the iStent, which is the smallest implantable device approved for use in the human body. It is a titanium device that is implanted from inside of the eye (an ab interno approach) into the trabecular meshwork in order to bypass it and improve outflow of eye fluid. iStents are typically implanted during the time of cataract surgery, and in some cases more than one iStent is implanted. Again, the benefit of iStent is its higher safety profile, but the downside is that it does not lower eye pressure to the same extent as trabeculectomy. As with other MIGS procedures, iStent combined with cataract surgery typically lowers eye pressure to the mid-teens.
In 2018, the manufacturer of the CyPass® micro-stent to treat glaucoma decided to voluntarily withdraw it from the market. Learn why the manufacturer took this step, and what you should do if you have already had the CyPass micro-stent procedure.
Xen is also a recently approved MIGS device that uses a gel microstent to create an ab interno trabeculectomy. In traditional trabeculectomy, a small hole is made in the eye wall, and a flap is created over it to make sure there is not too much fluid flowing out of the eye. In the case of the Xen, no incisions need to be made in the conjunctiva. Instead, the stent is placed through the eye wall and under the conjunctiva using a less invasive ab interno approach. However, the anti-scarring medications that we use with traditional trabeculectomy is often still used with Xen, thus there is no advantage of Xen over trabeculectomy in that regard. Furthermore, the Xen often requires more postoperative procedures done in the clinic because scarring still occurs.
There are many more MIGS devices and procedures that are in clinical trials but not yet FDA approved. It does seem that the landscape for glaucoma patients is changing. The general consensus is that MIGS may be appropriate for patients who have mild to moderate glaucoma, who are intolerant of or noncompliant with eye pressure lowering drops, who do not require a very low target eye pressure, and who are undergoing cataract surgery. Because these procedures are so new, it is hard to predict exactly where MIGS will fit in to the glaucoma treatment landscape. But it is an exciting time for the field as these new technologies develop and come to market.
Yvonne Ou, MD, is a board certified ophthalmologist who specializes in glaucoma, including medical, laser and surgical therapies; cataract evaluation and treatment including combined cataract and glaucoma surgery; glaucoma filtering and implant surgery; and newer procedures.
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