The overall picture for glaucoma surgery complications has changed with the introduction of new approaches and minimally invasive surgical interventions. Glaucoma Physician spoke with Brian Flowers, MD, a glaucoma specialist with Ophthalmology Associates in Fort Worth, Texas, for a closer look at the complications that glaucoma surgeons face today.
Q: How do you see the current landscape of complications in glaucoma surgery?
A: Looking back just a few years, our main surgical options were trabeculectomy, the Ahmed Glaucoma Valve (New World Medical), and the Baerveldt Glaucoma Implant (Johnson & Johnson Vision). In those days, there was a lot more postoperative maintenance, specifically with regard to trabeculectomy surgeries. It stands to reason that, if the surgeon is targeting an IOP in a specific range, at times you may miss high, and at times, you may miss low. This leads to the need to manage the complications that follow with interventions, such as bleb needlings, draining choroidal detachments, bleb revisions, and so on. Now, we have many more surgical options. This leads to a spreading out of the types of surgeries that we are doing. On a given surgery day years ago, I'd have multiple trabs and tubes, and now I'll have a variety. Currently, a typical day will include a trab, a tube, and multiple iStents (Glaukos), Hydrus (Ivantis) implants, and Xen (Allergan) surgeries. So there is much greater variety, and because there are fewer trabeculectomies, then almost by definition there are fewer complications. That's probably the biggest difference that I notice in my own individual experience, compared to several years ago.
With regard to complications, I feel the need to make a comment about the Xen procedure. In my mind, if you have to needle it, that means it's failed. The failure rate for Xen surgery has gone down as we transition away from an ab-interno approach to an ab-externo approach. I found Xen awkward to insert in an ab-interno fashion, and it can be less clear as to what plane the tube was going to end up in, so it can often be sub-Tenon or intra-Tenon and thereby scar down and affect flow. It's uncomfortable taking the patient to the OR and just hoping that the surgery would work.
Doing the surgery with an ab-externo approach means that not only is the surgery technically much easier, but also it's much easier to place the Xen implant in between the conjunctiva and Tenon’s, where it is less likely to scar. Results have been more predictable than with the ab-interno approach. I think it remains to be seen whether the long-term outcomes are similar to trabeculectomy. Certainly, the patient experience with the Xen is far superior to that with trabeculectomy. I'm optimistic.
Q: What about other MIGS devices; any specific complications to look for postoperatively?
A: With the Glaukos devices, there are virtually no complications. They’re very safe. The Hydrus came out in the past year and is also very safe. I believe any complications would be related to learning curve. I have returned to making a separate incision to allow the Hydrus to approach Schlemm’s canal at the ideal angle, facilitating easy placement. We were in the clinical trial, so I have many years of experience with the Hydrus, and I think it has done well in terms of pressure lowering and safety. In addition, any issues with nickel allergies are completely unfounded.
Q: So because surgeons are using more MIGS, the overall complication profile for glaucoma surgery is reduced?
A: I would certainly agree with that. Looking for options other than trabeculectomy and tube surgery has certainly decreased complications. Another “complication” that is not often discussed is induced refractive error. I had a patient recently who had previous cataract surgery. She was fairly young, and her vision was 20/20 uncorrected. Over time, her IOP got out of control, so we looked at her options. Trabeculectomy, which was one of the options we were considering, was definitely going to put her in glasses. It can be very difficult to do trabeculectomy without inducing astigmatism. Being able to do a Xen procedure or any of the nonpenetrating MIGS surgeries can allow that person to remain spectacle free. Ultimately, that is the option we chose. It's something we think about probably subconsciously but maybe don't articulate it often enough. In the age of refractive cataract surgery and higher patient demands for uncorrected visual acuity, many MIGS procedures allow patients to maintain spectacle independence that they otherwise would not have.
Also, I think being aware of implanting all suprachoroidal devices at the appropriate depth will be important for future devices. There are new devices by Glaukos and iStar that are in trials currently, so we may see some new ones in the future.
Q: And affecting the cornea is something that should be watched for any implant?
A: Any implant in the anterior chamber that protrudes at all has the potential to affect the cornea. We know that all the tubes we use do that, and Ahmed, Baerveldt, and Xen probably will if they’re in the eye long enough. I'm sure that what we learned from the Cypass will lead others to examine this issue much more carefully.
Q: Over time, what should surgeons be looking for after a patient has had a device for 5, 10, or even 20 years?
A: Each device probably has its own set of issues. I think with an implant, one of the things you're always concerned about is erosion or displacement of some sort. With iStents and with the Hydrus, we've been following these patients for a long time. For Hydrus, we have 5-year follow-up data, and I have several patients who've had them for a very long time. There's no evidence of any erosion or moving of the device in the eye. That's something that's watched for very carefully in clinical trials on any implants. We've been following the Cypass longer than that. I have patients who've had Cypass for 9 years with no issues. We will see about Xen, which is a subconjunctival device. We'll have to see in the long run how they compare to Ahmeds and Baerveldts when it comes to erosion.