It’s Friday, it’s the 13th, and the day of a super moon. The winds are howling outside with torrential rains pounding on the tiffany dome in the building’s foyer. Lights are flickering as the high winds interfere with the electricity. I sit alone; focusing on a pile of patient charts long after my staff has left for home. Slam! A door has closed. I look down the dark hall and see a light coming from beneath an exam room door. Feet shuffle. I exit my office and slowly walk down the hardwood-lined hallway, the floor creaking with with each step. My heart is racing, and my pupils dilated. I hear the theme music from the movie Halloween; ha-ha-ha-trab-trab-trab. Next, a high-pitched S-C-R-E-A-M: ahhhhhhhhh!!!! I scurry to the room to find a 6’1 man hovering over an elderly lady in the inclined position, muttering the words: “she has hemorrhagic choroidals AND this was her good eye”.
Although portions of my story are fictional, we all know the horrors that filtration procedures can bring. And although a necessary tool in our armamentarium, trabeculectomies are known to be are fraught with complications, both in the early postoperative period and even years or decades after the surgery. Because of this, we have typically limited our subjection of patients to this high-risk procedure in those suffering from severe disease, or in patients who display definitive glaucomatous progression. We shutter when having to perform such a procedure in the young, and especially those with early disease.
For decades, we have been hoping for alternatives to this highly invasive therapy. Thankfully, within the last five years, we have had an antidote in the form of micro-invasive glaucoma surgeries or MIGS. Although MIGS are not a replacement for filtering procedures, they have provided us with an alternative method for managing patients with uncontrolled mild to moderate disease. MIGS have also afforded us the option to augment cataract surgery in an effort to reduce or eliminate a patient’s medication burden.
The definition of MIGS varies based on the technique(s) involved, but safety is at the forefront of all MIGS options, along with moderate efficacy, an angle-based ab-interno approach, and conjunctival sparing. Most angle-based procedures, at least in my experience, can control the uncontrolled glaucoma patient, if performed in the right setting (i.e. performing a trabecular altering procedure in patients with pigmentary glaucoma OR conversely not performing a procedure like endoscopic cyclophotocoagulation in a chronic uveitic patient). There are times when an angle-based procedure would be insufficient or inappropriate, however, in which case a filtration procedure is indicated. We don’t always have to dig deep into our toolbox and pull out the biggest hammer—yes, I am referring to a trabeculectomy or an atomic bomb, whichever reference you prefer. We now have a more elegant means for creating a bleb, namely the XEN45 gel implant (Allergan, Dublin Ireland). First, let’s address the elephant in the room. Is XEN a MIGS procedure – and does its discussion belong in this MIGS blog? I’m not sure whether it 100% falls within the definition of a MIGS procedure, but it definitely subscribes to the idea of a “less-invasive glaucoma surgery” or a “MIGS-filter”.
The XEN45 gel implant was approved by the Food and Drug Administration (FDA) on November 22, 2016 and has continued to create a “buzz” in the glaucoma community. It is indicated for implantation in patients with refractory glaucoma where other surgical procedures have failed, or in patients with open angle glaucoma unresponsive to maximum tolerable medical therapy. Like MIGS devices, it is performed via an ab-interno approach. But, it is designed to create a conduit for aqueous to flow from the anterior chamber into the subconjunctival space, which ultimately creates a filtration bleb. The device itself is a soft, collagen-derived, gelatin implant that is 6 mm long and injected into the conjunctival space. Like other filtering procedures, an anti-fibrotic agent is needed to minimize subconjunctival fibrosis and maximize functional longevity.
The procedural aspects of XEN implantation are still evolving as we continue to learn more about the device and how eyes respond. While under investigation in clinical trials, a conjunctival dissection was required in-order-to treat the scleral bed and sub-Tenons space with mitomycin-C (MMC). We have since side-stepped this process and now inject the MMC directly into the subconjunctival space, either pre-operatively while the patient is in the holding bay or intra-operatively prior to creating incisions in the eye. Some surgeons use 0.2 mg/mL while other use up to 0.4 mg/mL. The concentration I choose depends on many factors, including a patient’s ethnicity, apparent Tenons thickness, and presence of previous conjunctival-based surgery. We have also considered varying methods and locations of implantation: sub-Tenons, intra-Tenons, supra-Tenons, superior nasal, and superior. Although some clinical investigators differ in their opinion on the best method for implantation, the universal opinion is that a supra-Tenons approach closest to the twelve o’clock position is best. There are many more factors that play a role, including patient ethnicity, number of pre-operative medications used, chronicity of medication use – and, of course, surgeon preference.
The XEN45 has certainly made filter creation easier when compared to a trabeculectomy and has eliminated the need to artfully place the perfect amount of tension on sutures over scleral flaps, which regulate fluid flow. However, it has not eliminated our need to fully understand how to manage a bleb. The shear reality is, despite XEN45 being a less-invasive glaucoma surgery, it is still a bleb-creating procedure. And, although there does appear to be a difference in bleb morphology, at least in the short-term, the bleb associated with the XEN45 gel implant is still a bleb. And a bleb is a bleb. In fact, I have found the need to manipulate my XEN blebs more frequently than with my trabeculectomy blebs (or Express mini-shunt, Alcon Laboratories Ft. Worth, TX) in the form of 5-fluorauracil injections or needling revisions. It is accepted that about 30% of blebs created by the XEN45 require needling revisions, which is consistent with what I’ve seen in my own practice. There have also been a few reports of implant extrusion with or without concomitant endophthalmitis, requiring device explanations (situations I have seen in my own practice).
BUT, I have found that recovery is incredibly quicker with the XEN45, which is a wonderful feature especially when treating monocular patients. I am able to perform all of my procedures under topical anesthesia augmented with preservative-free intracameral lidocaine. I do feel the blebs have a better morphology and appear to be more comfortable for the patient, but longer-term follow-up is necessary. To-date, I have not encountered hypotony (n ~ 125) but I know it is certainly a risk. It is relatively astigmatically neutral and the conjunctival alteration is minimal (depends on how diffuse the bleb is as well as degree of subconjunctival fibrosis), so I am comfortable using the Xen as a first-line filter because I know I can still perform a trabeculectomy of necessary. Because it is needled guided, I can precisely implant the device in-between or beyond areas of conjunctival scarring from previous surgery. In all, I have been very grateful that the XEN45 is now an option in the glaucoma treatment algorithm and am thankful for the fact that it has made the option of filtration much more palatable for my patients – and for my practice.View all blog posts
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