Minimally invasive glaucoma surgeries (MIGS) and angle-based glaucoma surgeries are becoming an increasingly common practice for the management of glaucoma, both in combination with cataract surgery and as a standalone procedure.1,2 The number of devices and techniques is rapidly expanding. Surgeons have access to viscodilation procedures that address all or most of Schlemm’s canal (iTrack Advance by Nova Eye Medical and Omni Surgical System by Sight Sciences) or that perform multiple localized viscodilations (Streamline; New World Medical). There are also a growing number of trabecular stripping procedures such as GATT (with suture or microcatheter), Omni, Kahook Dual Blade (New World Medical), Sion goniotomy blade (Sight Sciences), and the Trab-Ex gonitomy blade (MST). Finally, there are trabecular bypass stents, including the iStent implants (Glaukos) where either 2 (iStent inject) or 3 stents (iStent infinite) are placed, or the Hydrus Microstent (Alcon), which scaffolds approximately 3 clock hours of the canal while providing a trabecular bypass inlet.
Combined MIGS
More surgeries are being combined in the goal of further lowering intraocular pressure (IOP), increasing the duration of efficacy, better controlling disease apart from topical therapy, and minimizing risk of larger incisional glaucoma surgeries. Initial reports indicate good safety and efficacy when MIGS surgeries are combined.3,4 Angle surgery, however, is not without risk. Combining procedures adds surgical time in the angle, which increases the risk of patient movement as well as potentially compromising visualization of the angle through anterior chamber blood or progressive corneal edema.
The basics of performing good angle surgery (good visualization, proper head position, clear anatomic landmarks, appropriate scope tilt) are even more important when a surgeon is performing multiple procedures. The following tips are aimed at improving surgical success, cutting down on surgical time, helping to maximize visualization, and preparing for unexpected intraoperative results.
Figure 1. The tip of an iTrack Advance approaching nearly parallel to the trabecular meshwork while entering through a paracentesis toward the surgeon’s dominant hand. Image courtesy Zachary Vest, MD.
Tips for Performing Viscodilation With Trabecular Bypass Stent
1. Be flexible with your plan. The first key to being flexible is knowing when not to proceed with the preoperative plan, either because of atypical angle anatomy or because of an uncooperative patient. These surgeries are not without intraoperative risk, be it iris injury, cyclodialysis cleft formation, or Descemet detachment.
Meanwhile, the surgeon should be prepared to modify which type of MIGS is performed. The initial viscodilation can help decide which type of stent to use and where it should be placed. It is not uncommon to encounter strictures within Schlemm’s canal where a catheter will not fully cannulate the system. If the stricture cannot be opened, it may not be possible to place a larger Hydrus device; instead, multiple iStents could be placed without issue or a goniotomy could be selected instead of an implant.
Another issue that can occur is the angle may not deepen as significantly as expected after phacoemulsification. If that is the case, it may not be desirable to place a stent due to concern about future occlusion due to proximity of the iris, and either standalone viscodilation or addition of goniotomy with postoperative pilocarpine may be more appropriate.
Having multiple options available requires several steps. First, the patient needs to be aware that the initial surgical plan may change based on the intraoperative findings and must consent appropriately before the operation begins. The surgeon and surgical center then also need to be aware of the patient’s surgical benefits to know what surgeries are covered and available. The operating room staff need to be educated and prepared for the various surgeries that may be needed. For instance, if a case is posted as cataract surgery with Omni and Hydrus, and the staff opens both devices, what happens if the canal cannot be cannulated successfully with the Omni? The unused Hydrus is then typically wasted. Outside of the iTrack microcatheter, which takes time to prime, all other devices are not opened in our ASC until they’re asked for. Shortly after beginning the viscodilation, the appropriate stent or goniotomy device can be requested once the status of the canal is known.
2. Be comfortable passing implants, catheters, and blades backhanded. Being able to access the canal in either a clockwise or counterclockwise direction is invaluable. For instance, it is possible to create false passages with viscodilation catheters or with larger stents such as the Hydrus. Once a false passage has been created, it can be very difficult to find the true canal again. A safer option is to then perform the viscodilation and stent placement with a backhanded pass. Often this can be performed through the main wound, but for better angle of approach, the paracentesis created for one’s nondominant hand during cataract surgery works well. Some surgeons can perform this using their nondominant hand. However, the Omni surgical catheter can be flipped to allow clockwise or counterclockwise delivery, and the Hydrus and iTrack Advance have a rotatable delivery head, which allows for the surgeon to use the dominant hand to deliver the device in a backhanded direction. Ultimately, if the canal cannot be successfully cannulated, it may require the placement of a smaller stent or usage of a goniotomy to avoid the false passageway.
3. A paracentesis is the friend of every MIGS surgeon. Paracentesis incisions are invaluable during MIGS surgery. Working through a paracentesis helps minimize the egress of viscoelastic through the incision, which improves chamber stability and visualization. Most devices can access the angle through a standard paracentesis. Only goniotomy devices, which need a larger travel distance and can oar lock in a smaller incision, benefit from a larger incision.
If the case is being performed with cataract surgery, start the case by making 2 paracenteses, both approximately 4 clock hours from the nasal angle, one of which is the standard paracentesis for cataract surgery. If the surgeon waits until after phacoemulsification to make a paracentesis for the MIGS surgery, the eye is already soft, which can lead to an excessively long paracentesis. A long paracentesis will cause more striae and impair visualization.
The paracentesis location is important if the surgeon is accessing the canal with a device that has a curved inserter, such as the Hydrus, the iTrack Advance microcatheter, or the Omni. Having a paracentesis 3 or 4 clock hours away from the nasal angle toward the dominant hand allows for a more natural, parallel alignment to Schlemm’s canal (Figure 1). Accessing the angle through the main incision with these devices can lead to the device inserter having too steep of an approach, which increases the chance the device or catheter wants to pass out of the canal and track into the suprachoroidal space (Figure 2). Any curved device can be laid on the cornea to help estimate appropriate placement of the second paracentesis.
Figure 2. A steep angle of approach with an iTrack Advance handpiece placed through a standard main incision, which increases the risk of a catheter not successfully cannulating Schlemm’s canal. Image courtesy Zachary Vest, MD.
4. Be comfortable with working away from the nasal angle. If there are any issues accessing the nasal angle, other parts of the angle can be accessed if the surgeon is willing to shift their body position. This can be helpful if there is significant stenosis of the canal nasally or false passages have been created in the nasal angle. The superior or inferior angle can be accessed by having the patient look away from the surgeon and potentially tilt their chin up or down accordingly. Often, another incision is required to allow for an appropriate angle of approach.
5. Ways to minimize viscoelastic usage. If the visualization of the angle is compromised due to blood reflux into the anterior chamber, insufficient viscoelastic on the cornea, or a shallow chamber, then more viscoelastic is required. Visualization must never be compromised. Any of those situations can result in incorrect placement of a device, inadvertent cleft formation, or a Descemet membrane detachment during viscodilation. At the same time, having to open another package of viscoelastic can lead to increased operative time and extra expense. There are several options to cut down on viscoelastic usage.
The first option is to perform the MIGS portion of the case with a dispersive viscoelastic such as Viscoat (Alcon). If the case is being performed with cataract surgery, this is most easily done prior to cataract surgery. The visualization prior to phaco is excellent because there is minimal edema to the cornea. This also allows for a more stable anterior chamber, because dispersive viscoelastic is less likely to burp out of the incisions during surgical manipulation. The limitations to this approach are that the angle may not be sufficiently deep and more blood can reflux into the anterior chamber during the cataract portion of the case, impacting visualization.
In a standalone combined MIGS case, irrigation and aspiration would be required to remove the dispersive viscoelastic, because it is resistant to being evacuated with BSS irrigation alone and could lead to a spike in intraocular pressure (IOP).
Another option is to maximize the viscoelastics already opened for the case. For instance, the iTrack Advance delivers more viscoelastic during viscodilation than other systems, and it requires its own viscoelastic. When iTrack is being used to perform the viscodilation, the microcatheter can be left inside the eye and further viscoelastic delivered through the catheter to push any blood out of the angle and deepen the chamber prior to stent placement. This can save opening additional viscoelastic and reduces device handoffs, which can help decrease surgical time.
Conclusions
The combination of MIGS surgeries is a promising area of glaucoma management. However, for successful outcomes, a surgeon must be flexible in their plan, deliberate in their surgical technique, and open to taking extra time and effort to ensure surgical success and minimize the risk of complications. GP
References
1. Yang SA, Ciociola EC, Mitchell W, et al. Effectiveness of microinvasive glaucoma surgery in the United States: Intelligent Research in Sight Registry analysis 2013-2019. Ophthalmology. 2023;130(3):242-255. doi:10.1016/j.ophtha.2022.10.021
2. Williams PJ, Hussain Z, Paauw M, et al. Glaucoma surgery shifts among Medicare beneficiaries after 2022 reimbursement changes in the United States. J Glaucoma. 2024;33(1):59-64. doi:10.1097/IJG.0000000000002294
3. Porter MS, Wood BP, Gallardo MJ, Pederson A. A study of cataract surgery combined with canaloplasty and microtrabecular bypass stent surgery in open angle glaucoma. Presented at: the American Society of Cataract and Refractive Surgery; April 7, 2024; Boston, MA.
4. Wood BP, Porter MS, Gallardo MJ, Pederson A. Medication burden in 3+ meds glaucoma eyes following canaloplasty and micro-trabecular bypass implantation combined with phacoemulsification. Presented at: the American Society of Cataract and Refractive Surgery; May 6, 2023; San Diego, CA.
