The traditional glaucoma treatment paradigm is shifting.1 Historically, IOP-reducing drops and selective laser trabeculoplasty (SLT) have been used as first-line treatments to reduce IOP in patients with glaucoma, with incisional surgery reserved for advanced or progressive cases. With the advent of minimally invasive glaucoma surgery (MIGS), surgical intervention is being considered earlier.1,2 MIGS refers to a group of surgical procedures that share five qualities: ab interno conjunctiva-sparing approach; maintenance of normal anatomy through minimal trauma to target tissue; modest efficacy; high safety profile; and rapid recovery rate.3
MIGS may be considered for further IOP reduction when drops and laser are insufficient, to reduce medication burden, or a combination of the two. Most MIGS are performed at the time of cataract surgery, as the patient is already assuming the risk of intraocular surgery. If a glaucoma patient has a visually significant cataract and the provider recommends cataract surgery, the surgeon should consider and offer concomitant glaucoma surgery, MIGS or otherwise.2
In recent years, however, surgeons have demonstrated success with MIGS in situations in which cataract surgery may not be indicated or may have already been performed – which we will refer to as standalone MIGS. As examples, one can imagine the cases of a young, phakic patient with a clear lens and mild-to-moderate glaucoma on multiple medications, or the older, pseudophakic patient who developed mild-to-moderate glaucoma late in life. For both patients, lifelong adherence to complex drop regimens may be difficult. In fact, multiple studies have demonstrated that adherence to topical glaucoma medication regimens is low, and that decreased adherence is associated with disease progression.4,5 Additionally, for these two patients, traditional bleb-forming incisional glaucoma surgery may pose too great a risk for controlling their mild-to-moderate disease. In both cases, the surgeon can consider a standalone MIGS procedure to tackle two potential goals: further lowering IOP and reducing the amount of ongoing topical therapy required.
The use of standalone MIGS in the United States is limited by FDA-approved indications. This article will discuss only devices and procedures that are approved for standalone use at the time of publication. It is important to recognize that research is ongoing to explore the effectiveness of standalone MIGS beyond those which are presented here, and that the indications for use of MIGS devices and techniques may expand.
Standalone MIGS Options
Suture GATT
The original ab interno GATTs were described as a suture threaded into Schlemm’s canal through a clear corneal incision, then retrieved on both ends, completing a 360 trabeculotomy.6,7 The procedure is effective as both a combined procedure and a standalone procedure, with IOP reduction of 31% to 61% depending on the indication and preoperative lens status.6–8 It is thought that the use of multiple glaucoma medications compromises the distal outflow pathway and reduces effectiveness of this procedure, so this may be most appropriate in patients without long-term glaucoma drop use.
iTrack
The iTrack and iTrack Advance microcatheters (Nova Eye Medical Inc.) are lighted catheter devices that can be used in multiple ways. The device is inserted into an opening in Schlemm’s canal (made with a blade in the case of the iTrack, and with the device inserter itself in the case of the iTrack Advance) and threaded 360°, delivering micro-aliquots of viscoelastic throughout the canal to reduce points of blockage in the conventional outflow system. Upon completion of the canaloplasty, the surgeon may decide to perform a 360 trabeculotomy by retrieving the lighted tip of the device and retracting both ends.
Standalone canaloplasty with the iTrack device has been shown to reduce IOP by 25% to 40% and medication burden by 46% to 79% across disease severity and glaucoma type.1,9-12 The effect is comparable when performed alone and with cataract surgery.11,12 A recent review of literature found that standalone GATT performed with the iTrack microcatheter produced IOP reductions of 28% to 61% and medication reduction of 38% to 73% in studies with follow-up of 6 to 24 months.1,6,13
Omni Surgical System
The Omni Surgical System (Sight Sciences) is another device that combines the capabilities of canaloplasty and trabeculotomy. The Omni Surgical System requires a single surgical incision, and it can be used for trabeculectomy for fewer than 360° if complete 360° canalization is not possible due to strictures or presence of other canal devices. The device is inserted into the canal and deployed up to 180°.
Upon withdrawal into the inserter, viscoelastic is dispensed into the canal. It can then be re-inserted into the same passage, and a titratable trabeculotomy can be performed by unroofing the canal rather than withdrawing back into the inserter. Standalone canaloplasty with the Omni device has been shown to reduce the IOP by approximately 36%.14 The use of this device for standalone combined canaloplasty/trabeculotomy has been shown to reduce IOP by 27% to 40% with reduction of medications by 48% to 73%.1,15–18 The procedure has been shown to produce greater IOP reduction in patients with higher baseline IOP.15,18
Trabectome
The Trabectome device (MicroSurgical Technology) uses electrocautery to ablate the trabecular meshwork. The device is inserted through a single clear corneal incision. After engaging the trabecular meshwork, the device is advanced along Schlemm’s canal as the foot pedal controls the electrocautery. The standalone Trabectome procedure achieved IOP reduction of approximately 21% to 43% across multiple reviews and individual studies,1,19-22 indicating this is a valuable option for partially treating the angle in hopes of achieving further IOP control or medication reduction.
Kahook Dual Blade
The Kahook Dual Blade (KDB) (New World Medical) goniotomy device uses a two-blade system and ramp to excise trabecular meshwork tissue. Through a single clear corneal incision, the trabecular meshwork is engaged in the toe of the device, and the device is advanced along the canal, which is excised by the two-blade design. As a standalone procedure, it has been shown to reduce IOP by 28% to 46% and drop usage by 26% to 42%.1,23–26 The KDB design allows for safe, precise treatment of a portion of the trabecular meshwork, without the additional need for an electrocautery setup.
Sion
Sion (Sight Sciences) is another goniotomy device, which uses a bladeless system to excise the trabecular meshwork. The device is inserted through a clear corneal incision and the trabecular meshwork is engaged with the rounded tip of the device. The heel of the device is then relaxed onto the posterior wall of Schlemm’s canal, and the device is advanced along the canal, excising trabecular meshwork tissue. Although approved for use as a standalone procedure, data on its use in this clinical situation are limited.
iStent Infinite
The iStent Infinite (Glaukos) is the third iteration of the iStent microstent device. This iteration allows for placement of three wide-flange microstents anchored into the trabecular meshwork, two clock hours apart. The iStent Infinite system has been approved for use as a standalone device in primary open-angle glaucoma patients who have failed previous medical and surgical treatment. In a prospective study on standalone use, the iStent Infinite reduced IOP by 25%, and 43% of patients were able to reduce medication burden.27 The iStent Infinite is the only trabecular bypass stent currently approved for standalone use.
Conclusion
The continued development of safe, minimally invasive glaucoma surgeries will provide important therapeutic options for surgeons and patients who may require further IOP reduction, decrease in medication burden, or both. Although outside the scope of this discussion, which focuses on standalone MIGS, providers should also be aware of additional interventional glaucoma options, including long-acting medication implants such as the Durysta bimatoprost implant (AbbVie) and the iDose travoprost implant (Glaukos).
When faced with a glaucoma patient who does not require cataract surgery, whether they are phakic with a clear lens or already pseudophakic, surgeons can consider a standalone MIGS procedure. MIGS may improve IOP and reduce the reliance on complex medication regimens, which may be difficult to adhere to, uncomfortable, or insufficient.
When choosing a MIGS procedure, the surgeon must weigh efficacy and safety profile. Combined canaloplasty and trabeculotomy with available devices appear to produce the greatest reduction in IOP; however, they also carry the greatest risk of bleeding and IOP spike. In cases where less robust IOP reduction may be sufficient, the surgeon should consider trabecular ablation, goniotomy, or stent placement. Ongoing research may expand the standalone use for additional procedures, and familiarizing oneself with the current approved indications and research is essential.28 OM
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