What’s Hot in Microinvasive Glaucoma Surgery?

Rapidly evolving techniques and tools increase surgeons’ ability to address individual needs of glaucoma patients.

By Constance O. Okeke, MD, MSCE

Microinvasive glaucoma surgery (MIGS) was developed to solve a problem relating to traditional glaucoma surgery: namely, the uncertainty of complications from trabeculectomy and drainage implants. In 2006, the Trabectome (Neomedix) was launched. This device provided a way to safely lower intraocular pressure (IOP) by removal of juxtacanalicular trabecular meshwork (TM) tissue, thought to be the area of greatest outflow resistance. This tool provided an unprecedented ab interno approach to the angle that spared the conjunctiva and avoided the long-term risks of conventional surgery.

The iStent (Glaukos), launched in 2012, further advanced the advent of MIGS. Its target user was not mainly the glaucoma surgeon, but rather the anterior segment surgeon. The device gained US Food and Drug Administration (FDA) approval for use only in conjunction with cataract surgery. This small but mighty device, designed to bypass the TM, has proven to be effective for lowering IOP in mild to moderate open-angle glaucoma—especially, in my experience, when it is used to target specific outflow channels.

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While the mainstay treatment of glaucoma has long been the use of topical eye drops, the efficacy of this approach not only varies greatly between patients, but it also seldom yields the results expected because of poor patient adherence.1 Also, the chronic use of antiglaucomatous medications can lead to a host of ocular side effects such as foreign-body sensation, burning, tearing, change in iris color, and changes in periorbital anatomy, as well as systemic side effects such as headaches, pain, and depression.2,3

The widespread adoption of MIGS has substantially changed the way eye care providers recommend treatment options for glaucoma patients, as glaucoma is now treated as a surgical disease in its early stages. Performed as a standalone procedure or as an adjunct to cataract surgery, the various MIGS procedures can aid in restoring the natural outflow pathways in glaucoma patients. This year brought the introduction of four new MIGS procedures, all of which were designed as modifications or enhancements of previously established glaucoma procedures.

THE HOTTEST MIGS PROCEDURES

Ab Interno Canaloplasty

In November, at the American Academy of Ophthalmology (AAO) Annual Meeting, Ellex, which acquired iScience and its canaloplasty portfolio in 2013, introduced ab interno canaloplasty (ABiC). The FDA approved canaloplasty with an ab externo approach in 2007. It has been shown during the past 10 years to be a viable procedure that can effectively lower IOP in open-angle glaucoma patients.4 However, the technique has been perceived as a technically challenging surgical option, and this has limited its wide adoption. The ABiC procedure provides a simpler, internal approach to canaloplasty, and still retains the ability to reestablish the eye’s natural outflow drainage system. It involves the use of a patented microcatheter with an inner lumen to inject a high-viscosity viscoelastic material for safe and effective 360° dilation of Schlemm canal, the TM, and the outflow collector channels. The technique appears to achieve IOP lowering effects similar to those with the ab externo approach and can also be performed as a stand alone procedure or combined with cataract surgery.

Figure 1. Steps of ABiC Procedure: Make a clear corneal temporal incision; inject dispersive OVD into anterior chamber; create side port for the iTrack canaloplasty microcatheter (A). Prime the iTrack with Healon or Healon GV (Abbott Medical Optics) (B). Insert primed iTrack into anterior chamber; guide iTrack tip near to where otomy site will be; let the shaft of the catheter rest on the iris (C). Place OVD, followed by the gonioprism, on the cornea and direct attention to the TM (D). Create a small horizontal incision approximately 1 mm wide in TM (E). Using retina forceps (MicroSurgical Technology), grab the catheter about 2 to 3 mm from the distal end and insert tip of iTrack into Schlemm canal through the otomy site at a 15° angle (F). Once it is in, feed iTrack into Schlemm canal using small bites to prevent increase in size of the otomy. Follow progress by observing the positional red light (G). Slowly withdraw iTrack while steadily injecting OVD (H). Once these steps are complete, remove hemorrhage from the incision site and all dispersive OVD from the anterior chamber. Hydrate corneal wounds with watertight seal (I).

The technique for the ABiC procedure is similar to the approach of all MIGS procedures. A clear corneal temporal incision is made, and anesthetic is injected, followed by an ophthalmic viscosurgical device (OVD) such as Viscoat (Alcon), into the anterior chamber (Figure 1). As the OVD is released in the space of Schlemm canal behind the TM, this separates compressed tissue planes where there could be adhesions, thus dilating the canal and the more distal collector channels and improving aqueous outflow.

The clinical data at 6 months look very promising. In a population of 228 glaucoma patients, ABiC performed as a standalone procedure resulted in total reduction in mean IOP of 44.9% and 50% reduction in number of medications. ABiC performed in conjunction with cataract surgery resulted in total reduction in mean IOP of 36.9% and 100% reduction in number of medications.5

Kahook Dual Blade

Also in November at the AAO meeting, New World Medical, makers of the Ahmed glaucoma drainage valve, launched the Kahook Dual Blade (KDB) as a new MIGS option (Figure 2). The KDB was engineered to excise TM tissue using precision micromachining and laser-cutting technology. One of its key features is a ramp that puts the TM on stretch as the device is advanced, aiding in the clean excision of the TM by the parallel blades on either side. Similar to the Trabectome, the KDB allows aqueous to drain from the anterior chamber into Schlemm canal and the collector channels by unroofing the TM. Unlike the Trabectome, the tool is a single-unit, disposable device that does not require a separate unit to perform the technique and does not use a power source.

The initial approach of the KDB procedure is similar to the that described above for ABiC (see Watch It Now.) If the procedure is done in conjunction with cataract surgery, it can be performed before or after. It is typical for there to be a mild egress of heme into the anterior chamber through the collector channels.

Initial data presented at the recent AAO meeting look promising, with ease of use by surgeons, IOP reduction to the lower teens, and reduction of number of medications by more than 50%. However, these results are still in the early stages.6

Visco360 and Trab360

Figure 2. The single-use KDB device (A). Magnified view of the KDB tip (B).

Figure 3. The Trab360 device (A). Schematic of Trab360 insertion tube that had been fully advanced and is now being pulled inward to cut the overlying trabecular meshwork and expose Schlemm canal and the outflow channels (B).

Earlier this year a new company, Sight Sciences, released two new products with FDA approval. Visco360 is a single-unit disposable device that features an access cannula, a flexible injection tube, and a control wheel that advances and retracts the injection tube. At first glance, this device looks almost identical to the Trab360. Where they differ is that the Visco360 device also features an internally integrated infusion pump and reservoir for OVD that allows for controlled delivery of OVD anywhere in the anterior chamber.

With either device, the initial surgical approach is the same. After clear corneal temporal incision, anesthetic injection, OVD injection, insertion of the device into the anterior chamber, and placement of a goniolens on the cornea for adequate view, the tip of the cannula is used to pierce the TM, and the injection tube is inserted into Schlemm canal and advanced. The Trab360 instrument acts as a trabeculotome, a nonpowered device that manually cuts the TM, by pulling the injection tube internally once is has been fully advanced in Schlemm canal. When the procedure is performed in two directions, it has the ability to treat up to 360° (Figure 3). In early 4-month results, an average IOP reduction of 32% from baseline and average reduction of eye drops by one were reported.7

With the Visco360 device, after the tube is inserted into Schlemm canal in one direction, the control wheel is turned in the opposite direction, the injection tube is retracted, and there is a controlled release of OVD into Schlemm canal that has the capability of dilating the canal and the more distal outflow channels (see Watch it Now)

One feature that I have found intriguing with this device is the ability to perform a combined procedure using both trabeculotomy and viscocanaloplasty techniques in one eye. For up to 180°, one can insert and retract the injection tube to release OVD. Then, in the other direction, instead of retracting, one can pull the injection tube internally to cut TM and unroof the canal and outflow channels. Thus far clinical trial results are sparse, but data are soon to be released. Time will tell whether these devices will prove to be viable MIGS options.

CONCLUSION

In 2015 there was an explosion of new MIGS options to add to the armamentarium of glaucoma and anterior segment surgeons to treat glaucoma. What is exciting is that, just as we use glaucoma medications with different mechanisms of action so that in combination they have an additive effect on IOP-lowering capability, this is also now possible with MIGS. Examples include the combination of iStent and endocyclophotocoagulation, or ICE procedure, and the combination of trabeculotomy and viscocanaloplasty with the Visco360 and Trab360 mentioned herein.

The momentum of MIGS is here to stay, and it is important to stay on the cutting edge because there is still more coming down the pipeline. This is an exciting time with new glaucoma treatments and new hopes to give to our glaucoma patients. n

1. Okeke CO, Quigley HA, Jampel HD, et al. Adherence with topical glaucoma medication monitored electronically the Travatan Dosing Aid study. Ophthalmology. 2009;116(2):191-199.

2. Osborne SA, Montgomery DM, Morris D, et al. Alphagan allergy may increase the propensity for multiple eye-drop allergy. Eye. 2005;19:129-137.

3. Nelson WL, Fraunfelder FT, Sills JM, et al. Adverse respiratory and cardiovascular events attributed to timolol ophthalmic solution, 1978–1985. Am J Ophthalmol. 1986;102:606-611.

4. Lewis RA, von Wolff K, Tetz M, et al. Canaloplasty: three-year results of circumferential viscodilation and tensioning of Schlemm’s canal using a microcatheter to treat open-angle glaucoma. J Cataract Refract Surg. 2009;35(5):814-824.

5. Gallardo MJ. Comprehensive approach to MIGS: Data from the ABiC Case Series. Ellex iScience Inc. Data on file.

6. Lazcano G. Kahook Dual Blade (KDB) Survey: Initial Surgical Experience with the KDB. Presentation at: New World Medical breakfast meeting; November 15, 2015; Las Vegas.

7. Sarkisian S. New way for ab interno trabeculotomy: initial results. Poster presented at: American Society of Cataract and Refractive Surgery; April 17, 2015; San Diego.

Constance O. Okeke, MD, MSCE
• Assistant professor of ophthalmology, Eastern Virginia Medical School, Norfolk, Virginia
• Private practice glaucoma specialist, cataract surgeon, and MIGS coach at Virginia Eye Consultants, Norfolk, Virginia
iglaucoma@gmail.com
• Financial disclosure: Dr. Okeke receives honoraria for speaking and training from Neomedix and Glaukos, and she also receives research funding from Glaukos