While the variety of minimally invasive glaucoma surgery (MIGS) hasn’t changed (see previous coverage at bit.ly/35C9t6s ), the way that MIGS were used in clinical practice has altered due to COVID-19. In this article, I provide an overview of the variety of MIGS and their indications, some of the upcoming MIGS, as well as brief overview of how COVID-19 had changed our usage of MIGS.

MIGS

MIGS is a group of surgeries that allows for earlier, perhaps less complicated, surgical intervention while providing certain safety measures. Surgeons no longer need to constantly worry about hypotony and long-term bleb complications while deciding between trabeculectomy vs glaucoma drainage device. MIGS can be divided into several categories based on the site of action.

Trabecular bypass:iStent (Glaukos), Hydrus (Ivantis)

A significant portion of outflow resistance, the cause of elevated IOP, is met at the trabecular meshwork and the inner wall of the Schlemm. Therefore, trabecular bypass devices provide a shortcut for the aqueous fluid to flow into Schlemm’s canal.

In 2012, iStent was the first trabecular bypass device that came to market. Fast forward to 2020, and we now have iStent Inject W that is equipped with improved releasing mechanism of the implant.

Approved by the FDA in 2018, Hydrus is curvilinear in shape. It stents Schlemm's canal for three clock hours.¹

For billing purposes, both devices are indicated for mild to moderate open-angle glaucoma and are done in conjunction with cataract surgery. Research showed good results for both implants in standalone procedures.² We await FDA label updates for the use of device as standalone procedure.

Trabecular removal:
Trabectome (MicroSurgical Technology), Kahook Dual Blade (New World Medical), Goniotome (MicroSurgical Technology)

All the procedures mentioned here aim to remove certain degrees of trabecular meshwork to improve aqueous flow to Schlemm’s canal. Both Trabectome and Goniotome require connection to external machines, whereas Kahook Dual Blade doesn’t.

Be aware of prolonged recovery due to possible chance of bleeding after these surgeries. It would be great for patients to stop using blood thinners for a few days, but if patients have conditions, such as stroke or atrial fibrillation, then blood thinners should be continued.

Unlike trabecular bypass, goniotomy can be done as a standalone procedure and is indicated for mild, moderate, and advanced open-angle glaucoma. It also can be done with angle-closure glaucoma that has undergone goniosynechialysis.

Schlemm canal dilation:
iTrack (Ellex), OMNI (Sight Sciences)

In open-angle glaucoma, many patients’ Schlemm’s canals are compressed with downstream closing effect on collector channels. Ab interno canaloplasty (ABiC) aims to dilate these canals and open the proximal end of collector channels to decrease outflow resistance.

ABiC requires a scrub nurse to assist the surgeon with pushing viscoelastics while the iTrack is tracking through the canal. OMNI needs viscoelastic priming prior to usage, but the surgeon can perform the whole procedure alone.

These procedures are indicated for mild, moderate, and advanced open-angle glaucoma and can easily be combined with goniotomy for maximizing pressure-lowering effect. In terms of billing, only canaloplasty should be billed even if goniotomy was performed at the same time.

Subconjunctiva:
XEN (Allergan)

The XEN gel stent creates an artificial passage that channels aqueous fluid directly into subconjunctival space. Because of its diameter and length, it is powerful enough to lower eye pressure into the low teens without the theoretical risks of hypotony.

The surgery can be performed either ab-externo or ab-interno, depending on the patient’s anatomy. Mitomycin C (MMC) is often used during the surgery and possibly in the post-operative period if needling is needed. The concentration of MMC is optimized by the surgeon and can be administered via sponge or injection.

In terms of billing, there is a distinction between the ab-interno vs ab-externo approach. The internal approach involves Category III code, or a temporary code given to emerging technologies. Both can be done for mild, moderate, and advanced glaucoma, either standalone or combined with cataract surgery.

What’s to come

MicroShunt (Santen) is a biocompatible tube that creates a passage from inside the eye to subconjunctival space. Its diameter size is larger than XEN’s, therefore there is less risk of being clogged from inflammation and debris. It is approved in Europe but is in the premarket stage in the United States. Its indication will most likely be similar to XEN’s, and it can be used if XEN and its needling failed.

MINIject (iStar) is an angle-based procedure that targets the suprachoroidal pathway. The STAR-II trial and the two-year outcome of the STAR-I trial have encouraging results, with controlled endothelial cell density changes.^3,4 However, more time is needed to monitor for endothelial cell changes.

Effect of COVID-19

As we practice in California, COVID-19 has been a health concern since clinic reopened in late May. The overall goal is to control each patient’s glaucoma with minimal clinical visits. Talk to the physicians in your practice to see how they would best like to handle patient care in the pandemic. For me, I am more inclined to combine different sets of MIGS targeting different pathways in one setting to achieve greater IOP control and minimize subsequent follow-up. One example would be to combine Hydrus with canaloplasty and partial goniotomy.

Evolve and adapt

COVID-19 and 2020 have forced many of us to evolve and adapt. There have been many challenges, but at the same time, there are promising solutions. We are glad to say that MIGS plays a big part in the solution, and we're even more excited that several MIGS are undergoing testing and could potentially come to market in the next few years. OP

REFERENCES:

1. Samuelson TW, Chang DF, Marquis R, et al. A Schlemm Canal Microstent for Intraocular Pressure Reduction in Primary Open-Angle Glaucoma and Cataract: The HORIZON STUDY. Ophthalmology. 2019 Jan;126(1): 29-37.
2. Ahmed IK, Fea A, Au L, et al. A Prospective Randomized Trial Comparing Hydrus and iStent Micro-invasive Glaucoma Surgery for Standalone Treatment of Open-Angle Glaucoma: The COMPARE Study. Ophthalmology. 2020 Jan;127(1):52-61.
3. Denis P, Hirnei C, Durr GM, et al. Two-year outcomes of the MINIject drainage system for uncontrolled glaucoma from the STAR-I first-in-human trial. Br J Ophthalmol. 2020 Oct 3;bjophthalmol-2020-316888.
4. Feijoo JG, Denis P, Hirnei C, et al. A European Study of the Performance and Safety of MINIject in Patients With Medically Uncontrolled Open angle Glaucoma (STAR-II). J Glaucoma. 2020 Oct;29(10):864-871.