As with prior years, MIGS, or Micro-Invasive Glaucoma Surgery, continues to garner significant interest amongst attendees of the American Society of Cataract and Refractive Surgery. Several courses at the 2021 ASCRS meeting, the largest international live meeting in the U.S. since the start of the pandemic, were once again dedicated to MIGS surgeries and techniques. Our course, IC-112 - Minimally Invasive Glaucoma Surgery for the Comprehensive Ophthalmologist: Exploring Various Microstents and Devices, attracted a packed audience for a 90-minute set of lectures (that extended to two hours) covering eight different surgeries.
Dr. Daniel Terveen discussed the use of the Kahook dual blade, or KDB, to perform trabeculotomy. A single-use device with dual blades are used to cleanly excise a 90 to 120-degree band of trabecular meshwork, thus opening the internal wall of Schlemm’s canal to create a direct outflow pathway to the collector channels in the quadrant opposite to the corneal incision, most commonly the nasal quadrant for a temporal approach.
Dr. Arsham Sheybani next discussed how he utilizes GATT—or Gonioscopy-assisted Transluminal Trabeculotomy. As a procedure that can perform 360 degrees of trabeculotomy, it provides the greatest ability to increase outflow in the anterior chamber. Furthermore, with the use of a suture, it can be performed without expensive equipment or supplies.
I proceeded in describing the various methods of implantation of the Xen gel stent that have become popular since the approval of the device in 2016. This stent is a 6-mm long microshunt that is the size of a human hair. It completely bypasses the normal aqueous outflow pathways in the eye and, as such, most closely bridges the gap between other MIGS surgeries and traditional glaucoma procedures such as trabeculectomy and aqueous drainage devices. The original Xen surgery has been modified to improve efficacy while retaining its low complication rate. In addition to the traditional ab interno method, there are a growing number of surgeons who have converted to an off-label ab externo approach for even greater efficiency.
Dr. Steve Sarkisian explained the OMNI Surgical System, a dual procedure device that performs ab interno visco-dilation and canaloplasty along with 360 degree goniotomy. Dr. Mahmoud Khaimi discussed the similar iTrack Surgical System which accesses, catheterizes, and viscodilates the trabecular meshwork, Schlemm’s canal, and also the distal outflow system, beginning with the collector channels. Ab interno canaloplasty (ABiC) is unique amongst MIGS surgeries in that it does not introduce any device into the eye, nor does it result in any tissue destruction.
Dr. Paul Harasymowycz showed how the Hydrus stent by Ivantis can lead to a significant reduction in intraocular pressure when combined with cataract surgery. For MIGS surgeons, it is a relatively large stent at 8mm length, but due to its unique flexible design made of nitinol, the insertion into the trabecular meshwork is made with relative ease. One of the most important parts of the procedure is placing the corneal incision proximal to the desired insertion point of the device such that the approach angle to the meshwork will allow for smooth insertion of the device as it follows the natural arc of the angle.
Dr. Inder Paul Singh next showed how the latest generation of iStent, the iStent inject W, improves upon prior designs. The injector is better designed such that each stent is more easily deployed with less chance of the device becoming obstructed in the injector. Due to the wider flange of the iStent W, it is less likely to be deployed too deep and become lodged completely within Schlemm’s canal as could occur with the prior generation. As with past dual stent deployments, the target separation between devices is 2 clock hours for maximal intraocular pressure reduction. Finally, Dr. Singh showed images and videos depicting the maximal collector channel drainage activity in the nasal and inferior quadrants of the eye, which correspond well with the target location of most MIGS surgeries.
I returned to the dais for a final discussion on the MIGS technologies offered by MST, well-known for its Malyugin ring and microinstrument sets. The TrabEx+ and TrabEx are their single use devices that function like the KDB and other similar devices. The chief difference is that the angle of articulation of their blades is a bit greater than 90 degrees and the blades are serrated, which arguably allows for easier progress through trabecular meshwork. Whereas TrabEx is a standalone blade that is utilized in a viscoelastic-filled anterior chamber, the TrabEx+ has irrigation and aspiration ports built into the handle, which connect to the surgeon’s usual phacoemulsification equipment on I/A mode. As such, no viscoelastic is needed to perform this procedure, which is especially helpful in standalone cases for efficiency. Furthermore, the I/A feature allows the procedure to be performed in a dynamic anterior chamber, as opposed to the static anterior chamber of a viscoelastic-filled eye. By turning off I/A, the chamber shallows and blood refluxes into Schlemm’s canal, turning the trabecular meshwork a light red color. This allows for easy identification of meshwork in lightly pigmented eyes, which I have found to be extremely helpful in certain cases.
MST’s flagship device remains the trabectome, the first device approved in the U.S. for micro-invasive glaucoma surgery. The trabectome employs electrosurgery (not cautery) to ablate trabecular meshwork, thereby performing ab interno trabeculotomy as with their single-use devices. The electrosurgery results in instant destruction of the internal trabecular meshwork with easier gliding of the device through Schlemm’s canal. Trabectome is a standalone capital equipment that has a self contained I/A and requires disposable surgical packs that include everything required to perform the procedure (except for a goniolens and BSS bottle).
Notwithstanding the recently announced sudden and severe decline in reimbursement for certain stent-based MIGS surgeries, the surgeons in this panel all continue to utilize MIGS procedures routinely for the benefit of their patients. Interest in these techniques from attendees at ASCRS remained high, evidenced by the sold-out accompanying wetlabs the following day.
Rahul T. Pandit, M.D. is the medical director at Houston Methodist Hospital Ophthalmology Operating Room. Dr. Pandit reports no conflicts of interest.
