For those of you who don’t know, an undertow (or rip current) is when a narrow current that strongly flows away from shore cuts through the normal wave pattern. It can force even the best swimmer miles away from shore. The end result? Panic, exhaustion and possible demise. Before entering any body of water it is imperative to know all of the associated risks and how to deal with each adverse event.
Sounds familiar to what we do in surgery, right? Surgery can be complex, especially glaucoma procedures. Traditional filtration procedures are fraught with complications, but in experienced hands these complications can be minimized and, most times, the procedures performed to great success.
The advent of micro-invasive glaucoma surgery (MIGS) has propelled us into calmer waters, minimizing the incidence of post-operative complications – especially those that are vision threatening. Because of their safety profile, many surgeons, including our non-glaucoma trained skippers, have adopted and regularly perform MIGS. We started by wadded our way through the trabecular outflow system, bypassing the trabecular meshwork with the trabecular micro-bypass iStent (Glaukos Corporation, Laguna Hills, CA), but required inquisitive minds to understand the nature of fluid flow through the distal system and thereby how to best target stent placement to maximize outflow and efficacy.
Since then, we have had a plethora of devices and procedures that have hit the market, most that work by augmenting the conventional outflow system, such as ab-interno canaloplasty (ABiC) using the iTrack microcatheter (Ellex) and goniotomy using the Kahook Blade (New World Medical). Of course, we do have another physiologic system of outflow – one that is not well understood and somewhat unchartered, but that which can account for up to 60% of drainage – the suprachoroidal space. Because of the elastic properties of the uveal tissue, a negative pressure gradient exists between the suprachoroidal space and the anterior chamber, which can provide for a pressure driven pathway by detaching the ciliary muscle from the scleral spur. Fuch et al was the first to report the effects of cyclodialysis cleft creation during cataract surgery and its effects on IOP. Since then, our mentors had toyed with cleft formation in managing glaucoma patients, but encountered variable success and inadvertently entered the dangerous waters of dealing with hypotony. Most have since stopped using this as a procedure for glaucoma management. My mentors certainly were not creating cyclodialysis clefts to manage their glaucoma patients – not even in the most severe cases. My exposure to cyclodialysis clefts was therefore limited to those that were developed from trauma only. Despite its promise and its broad oceanic surface area for aqueous attraction, this method for pressure reduction has virtually died. In fact, if one were to search PubMed for cyclodialysis clefts, almost all results dating back to the 1970s will lead to manuscripts on cleft management and repair as opposed to cleft creation or glaucoma management.
But we (meaning guys/gals wiser and more innovative minded than myself), saw the utility offered by the suprachoroidal space and continued to develop procedures and devices to use this fluid siphon. We have since seen a number of devices designed to ferry fluid from the anterior chamber into the suprachoroidal space, some introduced via an ab-externo approach (Gold Micro Shunt (SOLX Inc.; Waltham, MA), Aquashunt (OPKO health Inc.), STARflo (iSTAR Medical), and Esnoper-Clip implant (AJL Ophthalmics,A´lava) all in clinical trials/development, while others are delivered in a more 'MIGS-y' way; the CyPass supraciliary micro-shunt (Alcon Laboratories,), which is already FDA approved and the iStent Supra (Glaukos Corporation), also currently in clinical trial.
Despite its approval in the spring of 2017, I think it is fair to say that the CyPass supraciliary micro-shunt has not been globally adopted by all that perform MIGS. One can speculate as why, but I presume it so because surgeons are simply comfortable with the MIGS procedures they already performing or because of the historical fear of dealing with or encountering complications of the suprachoroidal space. Just the word 'choroid' can be anxiety provoking when one couples it with the word 'surgery', like hearing the word 'shark' while on the beach. I did cataract 'surgery' yesterday and my patient coughed last night and now has a supra-'choroidal' hemorrhage. I did a filtration 'surgery', and despite having pressures in the low teens, the patient has kissing 'chroidals'. So I totally understand the fear of dealing with the space and/or device, especially because in the U.S., we have to implant the device in conjunction with cataract surgery. Though the risk for encountering adverse events (AE) is only slightly higher than stand-alone cataract surgery, the risk profile for supraciliary shunt implantation is a bit different and RARELY, can lead to prolonged recovery. The difficulty at hand is our society has become accustomed to the ideal of immediate perfection and any minutia of prolonging recovery, even in the most well informed patient, is quite unacceptable to the impatient patient. BUT, in experienced hands, the incidence of AEs with CyPass implantation are relatively rare, and, just like riptides off the shore, when encountered, can be overcome.
I am not trying to downplay or minimize the potential complications that can occur by manipulating the suprachoroidal space. Adverse events can and do occur. We’ve seen myopic shifts, clinical and numeric hypotony, pressure spikes upon cleft closure, anterior and posterior migration of the device and chronic iritis. But understanding the potential risk and properly educating patients in the pre-operative period can make the management of these adverse events much easier. To understand the relative risk of these adverse events one can simply read the Compass Trial. Hypotony, as defined as IOP less than 6 mmHg, occurred in only 2.9% of patients, while hyphema development occurred in 2.7% of patients, both of which were transient in nature. Aside from AEs reported in the Compass Trail, we have also discussed the occurrence of myopic shifts, but to date, only 50 cases out of close to 14,000 have been reported. In my own experience, those patients that develop myopic shifts and hypotony resolve within 6 months with conservative care.
So yes, issues can arise and you must prepare yourself and the patient. Myopic shifts can lead to a delay in surgery of the fellow eye and anisometropia – not to mention impatience and frustration for the patient. We have yet to determine the exact etiology or the type of patient that is a definitive risk for developing this phenomenon. Despite these differences in risk profile, many surgeons have adopted the technology because it is very effective at reducing IOP and medication burden. So how do we determine for whom we choose – and don’t choose – CyPass implantation? Some say to use the Compass Trial as a guide or “compass” in selecting those patients that qualify for CyPass implantation. It is recommended to choose those patients with open angles (Shaffer grade 3 or 4) and a medicated IOP of 25 mmHg or an unmedicated IOP between 21 and 33 mmHg. Some also argue to avoid high myopes or hyperopes because of heightened risk for choroidal effusion. The CyPass supraciliary shunts does work well and has worked well in my own patients with mild to moderate primary open angle glaucoma undergoing cataract surgery. I’ve even seen, on occasion, pressure reduction from the high 20ss/low30s to the low teens.
I’ve said before that the conventional outflow system is my primary target for facilitating outflow because of the safety provided by the back wall of the episceleral venous system — a safety net for hypotony development. But, at times, the conventional outflow system may not be amendable to successful modification. Though there may be some age related changes to the flow conductivity of the sclera, there have not been any reports suggesting the suprachoroidal space is diseased in glaucoma patients like the conventional outflow system. Because of this I tend to use a CyPass in those eyes with more severe disease and in a perfect world, would be able to choose it for some of my severe glaucoma patients. But we have what we have.
I say to you who are still on the edge of the pier, don’t be afraid of innovation. The literature supports the safety and efficacy of our suprachoroidal/supraciliary micro-shunts. Understand the pros and cons of each MIGS device and all potential adverse events that can occur. If you are comfortable dealing with the waters of the outflow system, go ahead and take a dive into the suprachoroidal space — it is summer after all.View all blog posts