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Having explored the various options available for micro-invasive glaucoma surgery (MIGS), I now use several devices with success. One MIGS device (XEN Gel Stent, Allergan) differs from the others in that it drains aqueous into the subconjunctival space and can be performed as a stand-alone procedure without cataract surgery or combined with cataract surgery.
By Davinder S. Grover, MD, MPH; Special to Ophthalmology Times
Dr. GroverHaving explored the various options available for micro-invasive glaucoma surgery (MIGS), I now use several devices with success. One MIGS device (XEN Gel Stent, Allergan) differs from the others in that it drains aqueous into the subconjunctival space and can be performed as a stand-alone procedure without cataract surgery or combined with cataract surgery.
Because the glaucoma treatment is a relatively safe procedure with the potential to remove patients from medications or use fewer drops,1,2 it can meet many needs of my glaucoma patients, including control of IOP, reduction or elimination of compliance issues, lowering of prescription costs, a healthier ocular surface, and a better quality of life.
My initial experiences using the gel stent procedure took place outside the United States, and then I became involved in both phases of its FDA trial. I trained with both Allergan and its affiliate, AqueSys, whose practice labs have model eyes and injectors that let physicians learn the feel of the injector and the proper location of the stent. I used various injector types and both the 140-μm and 45-μm inner lumen versions-the latter of which is now approved by the FDA.
In the past 5 years, I have placed about 150 implants, including about 75 since its FDA approval. The glaucoma treatment system is without question the safest, least invasive, most effective, and most predictable glaucoma procedure for creating a new drainage system.3-5
It has substantially decreased the number of trabeculectomies and tube shunts that I perform.
I choose the gel stent procedure for patients with advanced open-angle glaucoma when there is suspicion that the inherent drainage system (collector channels) is no longer functional. I also perform it on patients who have failed angle-based surgery, such as gonioscopy-assisted transluminal trabeculotomy (GATT) or surgery with a dual blade (Kahook Dual Blade, New World Medical).
If a patient is very active or taking blood thinners, I may move to the gel stent procedure instead of angle-based surgery given the risk of hyphema in the immediate postoperative period.
The procedure is not an easy surgery (but then again, neither is cataract surgery), and it cannot be mastered after one case. It has a lot of subtleties in terms of comfort with the injector and anatomy of the orbit, angle, and conjunctiva. I felt somewhat comfortable placing the stent after about 5 cases, and I would say I felt very comfortable after 10 to 15 cases.
Comparing this with my first 50 cataract surgeries, it is clear that while it takes a few cases to feel comfortable with the gel stent procedure, it is easy to learn and can be performed by most surgeons with proper knowledge and training.
The best advice I can offer is to practice using the injector before going to the operating room. Take an injector home, practice using it with the dominant and non-dominant hand, and hold the injector in various positions until the best position is found. Practice with the injector 10 to 15 times in the practice lab, keeping in mind that the ideal surgical placement is in the subconjunctival space (anterior to Tenon’s capsule).
The key to success was selecting the right candidates for the initial learning curve. The stent’s indications outline the patients and situations for which the device is approved, but first cases require a bit more selectivity for any new procedure.
The ideal first patient has an eye matching one’s dominant hand (the right eye, in most cases). I looked for patients who were pseudophakic and did not require a combined phacoemulsification procedure. Their coagulation state had to be normal. The angles were all grade IV without peripheral anterior synechiae (PAS) in the superior quadrant. I also wanted patients with prominent eyes and low cheekbones.
My first few cases went well. I gave the patients a peribulbar block to make the procedure easier, but I now do most cases under topical anesthesia. I gave the patients 20 to 40 mcg of mitomycin C (MMC) in the preoperative holding area, injecting the MMC under the posterior subconjunctival space at 12 o’clock and “rolling” the medication into the superior nasal quadrant. The implant is best placed when 1 mm is in the anterior chamber, 2 mm in the intrascleral space, and 3 mm in the subconjunctival space.
The initial thought was that the implant could be placed in the superior nasal angle without the assistance of a gonioprism. While this makes the procedure slightly easier initially, I found that I was not routinely injecting the implant exactly where I wanted it to be in the angle. Sometimes I was anterior to the trabecular meshwork (TM), sometimes I was through the TM, and sometimes I was posterior to the TM.
Now, I place the implant with the help of a gonioprism and feel that I am placing the stent more routinely just anterior to the TM (the ideal position in my mind).
Other early challenges
Another challenge early on was trying to avoid a “flick,” or having the injector move rapidly once the stent has been fully inserted.
I have learned to avoid this flick by removing the second instrument from the eye after the slider has been advanced 50%. I then let the eye return to its normal position and ensure that I am not applying any torque to the eye. Only after confirming this do I continue to slide the injector and complete insertion.
In a few cases, I struggled with patients’ prominent cheekbones, which can make it difficult to use the injector at the right angle (the reason I now count this among the features to avoid in early patients).
I also had difficulty maintaining proper control of the eye without applying a lot of pressure and traction on the corneal wounds. It also was easy to forget to maintain forward pressure (or bias) as I injected the implant, sliding the injector anteriorly.
The beauty of this surgery is that it is minimally invasive and forgiving. It does not cause a tremendous amount of trauma or collateral damage to the eye.
If the surgeon is not happy with placement and location of the implant, it is very easy to remove it, reload the injector, and re-insert the implant. If the surgeon is not happy with the placement and feels that the stent is too short in the subconjunctival space or perhaps too close to the cornea in the anterior chamber, the surgeon should remove it and insert it again.
It is much easier to take the extra time in the operating room to make sure the implant is in the ideal position than to be unhappy with the position and learn after surgery that the implant is too short in the subconjunctival space or too close to the iris or cornea in the anterior chamber. To remove the implant (which the surgeon should also play with in the practice lab), simply use microsurgical forceps to purchase the tip of the implant in the anterior chamber and gently pull, with one slow motion, the implant out of the eye.
My patients have done quite well. Most patients have a substantial decrease in IOP and glaucoma medications. In a peer-reviewed study of 65 patients, my colleagues and I saw a decrease in IOP of 20% or greater in 75.4% of patients, with a mean change of −9.1 mm Hg, while patients saw a mean decrease from 3.5 to 1.7 medications.6
The eyes typically look amazing on the first day (from a glaucoma surgeon’s perspective!). Visual recovery is very rapid, as is the return to normal physical activity. I have to perform a needling technique in roughly one-third of patients. The needling technique is slightly different from the technique used with a trabeculectomy, however, and it can be safely and easily done at the slit lamp. I typically augment bleb needling procedures with 10 to 20 mcg of MMC.
Very few of patients have had failures. The procedure is a true glaucoma surgery, so bleb needling, IOP spikes, erosions, hypotony, and choroidal detachments are possible. The beauty of the procedure is that these complications occur much less frequently than they do with traditional trabeculectomy and tube shunt surgeries.3-5
Davinder S. Grover, MD, MPH
Dr. Grover is attending surgeon and clinician, Glaucoma Associates of Texas, Dallas. He is a speaker/consultant to Allergan and Reichert Technologies, and a consultant to New World Medical.
1. 510(k) Summary: Allergan XEN Glaucoma Treatment System. FDA. Nov. 21, 2016. Accessed online Jan. 24, 2017. https://www.accessdata.fda.gov/cdrh_docs/pdf16/K161457.pdf
2. Pérez-Torregrosa VT, Olate-Pérez Á, Cerdà-Ibáñez M, et al. Combined phacoemulsification and XEN45 surgery from a temporal approach and 2 incisions. Arch Soc Esp Oftalmol. 2016;91:415-21. doi: 10.1016/j.oftal.2016.02.006.
3. Samuelson TW, Katz L, Wells J, et al. Randomized evaluation of the trabecular micro-bypass stent with phacoemulsification in patients with glaucoma and cataract. Ophthalmology. 2011;118:459-467. doi: 10.1016/j.ophtha.2010.07.007.
4. DeBry PW, Perkins TW, Heatley G, et al. Incidence of late onset bleb-related complications following trabeculectomy with mitomycin. Arch Ophthalmol. 2002;120:297-300.
5. Edmunds B, Thompson JR, Salmon JF, Wormald RP. The National Survey of Trabeculectomy III. Early and late complications. Eye (Lond). 2002;16:297-303.
6. Grover DS, Flynn WJ, Bashford KP, et al. Performance and safety of a new ab interno gelatin stent in refractory glaucoma at 12 months. Am J Ophthalmol. 2017 Aug 4.