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With its ability to restore the eye’s natural outflow pathway, ab-interno canaloplasty (ABiC) presents a viable option for the treatment of different stages and severities of glaucoma, according to Mark J. Gallardo, MD.
By Mark J. Gallardo, MD; Special to Ophthalmology Times
Dr. GallardoToday’s glaucoma specialists are more fortunate than ever-as managing their patients’ condition no longer requires a reliance on medication at one end of the treatment spectrum, and tube shunts and trabeculectomy at the other.
It is undeniable that trabeculectomy and tube shunts are effective at lowering IOP and slowing disease progression, and undoubtedly play a key role in the treatment of glaucoma. However, they may increase the risk of numerous peri- and postoperative complications.
Since these complications can be difficult and time-consuming to manage, surgeons are increasingly turning to less-invasive procedures that deliver reductions in IOP and medication use and may be associated with fewer complications.
Restoring outflow with MIGS
Another limitation of filtering surgery is that it works by circumventing-rather than restoring-the natural outflow pathway, which consists of the trabecular meshwork, Schlemm’s canal, and collector channels.
The past several years have seen the arrival of numerous devices and techniques for minimally invasive glaucoma surgeries (MIGS), which address specific, different aspects of the ocular outflow system.
One of the most interesting forms of MIGS, however, is ab-interno canaloplasty (ABiC).
An evolution of traditional canaloplasty, ABiC addresses all aspects of the outflow pathway. It is also the only non-ablative FDA-approved MIGS indicated for use outside of cataract surgery, and is the only MIGS to address the collector channels, which have been shown to play a key role in blocking aqueous outflow.1,2
Like its predecessor (canaloplasty), ABiC uses a patented microcatheter (iTrack, Ellex Medical Lasers Ltd.) to provide 360° viscodilation of Schlemm’s canal through a clear corneal incision. Unlike canaloplasty, the procedure does not require a tensioning suture. ABiC also preserves conjunctival tissue, allowing surgeons to perform future procedures if necessary.
In the past, if a patient was on maximum pharmacologic therapy, had an above-target IOP, and was at risk of progression, I would go straight to filtering surgery.
ABiC has become my first-line treatment for such patients, however, primarily because it is effective and involves minimal recovery. Also, it does not preclude me from performing other surgeries in the future-if I have a patient in which response to ABiC treatment failed, I can always do filtering surgery later.
Since rejuvenating patients’ natural ocular outflow system in this manner, the need for further surgery has dramatically reduced. I was averaging close to eight filtering surgeries per week, but now I only need to perform about one filtering surgery per month because ABiC and other MIGS procedures have proven to be so effective.
The second subset of glaucoma patients in whom I tend to use ABiC first-line are those undergoing cataract surgery while controlled on medication. I use cataract surgery as an opportunity to eliminate the medication burden by also performing ABiC.
When we are heading to the operating room, I mention to patients that we will “flush out” their ocular drainage system and rejuvenate their natural filter, which will reduce their need for medication. Most patients are completely unfazed by this.
For patients who are not controlled on medication and need incisional surgery, I let them know I am going to try to utilize their natural drainage system, which will require only a short recovery period.
I also tell them that if the procedure does not work because their natural filter is severely damaged, I may need to perform another surgery to bypass their drainage system at some time in the future. Patients are quite open to this.
A key advantage of ABiC is that it can be used in all stages of glaucoma, although findings from my own case series study indicate that is most efficacious in mild-to-moderate disease. I recently undertook a 12-month study in 64 patients with mild-to-moderate glaucoma who underwent ABiC either alone or combined with cataract surgery. Overall, the mean IOP fell from 18.4 ± 6.2 mm Hg preoperatively to 14.1 ± 2.6 mm Hg (p< 0.037) at 12 months postoperatively-a reduction of 30.64%.
Medication burden was also reduced, from 2.45 ± 0.89 at baseline to 0.79 ± 0.90 at 12 months postoperatively (p< 0.0001)-a reduction of 67.75%.
A subset analysis showed the procedure was effective when performed alone and when combined with cataract surgery. With ABiC alone, there was a 26.34% reduction in IOP and 59.43% in medication at 12 months postoperatively. When combined with cataract surgery, IOP fell by 28.57% and medication use by 74.1%.
I have also evaluated ABiC in patients with severe glaucoma. These patients do not do quite as well as those with mild-to-moderate glaucoma, most likely because the distal drainage system in severe patients is usually in an advanced state of disease. Nonetheless, I still tend to use ABiC as a first-line treatment for patients with severe glaucoma to try and avoid invasive filtering surgery. I’m comfortable doing this knowing that I still have around an 80% chance of filtering surgery-for 2 years at least.
Though ABiC is suitable for the majority of patients with glaucoma, it is not a panacea. Some patients will gain less from the procedure. For the most part, it requires a relatively well-functioning trabecular meshwork. Consequently, ABiC is of little benefit for patients with a diseased trabecular meshwork, because aqueous still has to traverse this structure to enter Schlemm’s canal.
I am often asked about the treatments I choose for a given patient and how I choose them. The simplest answer is that I try to tailor treatment according to my patients’ needs. However, for cataract patients with glaucoma, I always add a MIGS to reduce IOP or medication use.
Gonioscopy is an important tool in my preoperative evaluation. If I see a patient with a relatively diseased trabecular meshwork and a variegated pattern of pigmentation, I like to perform some form of trabecular microbypass or trabecular ablation. In all other patients, if I see a relatively normal-looking drainage angle, I use ABiC.
ABiC is not the only MIGS I use in my practice. I implant quite a few stents (iStents, Glaukos) and perform other ablative procedures as well. I tend to use the stent instead of ABiC if the trabecular meshwork appears diseased. In patients with pseudoexfoliative, pigmentary, or uveitic glaucoma, I prefer trabecular ablative procedures, such as gonioscopy-assisted transluminal trabeculotomy (GATT) or focal goniotomy with a dual blade (Kahook Dual Blade, New World Medical).
Mix and match
At times, I mix and match procedures depending on the patients’ disease stage, IOP, and appearance of the drainage angle. Furthermore, I use endocyclophotocoagulation as an adjunct to the aforementioned procedures. All of these techniques work very well.
Many glaucoma specialists experience an additive effect by mixing and matching different MIGS procedures. I have recently starting using the dual blade with ABiC in my patients with more severe glaucoma, as this ensures that aqueous fluid has a direct route into Schlemm’s canal.
In primary open-angle glaucoma, there is a fusion of trabecular lamallae, increased extracellular matrix proteins, juxtacanalicular tissue, and loss of intra- and intercellular micropores-all of which increase resistance to outflow and potentially reduce the effective filtration area. Adding a focal goniotomy produces an additive effect and makes me feel more confident that aqueous will reach the newly dilated canal and distal system.
All existing glaucoma treatments have a place in the management of the disease, but MIGS have undoubtedly increased the options. Its ability to remove all potential ocular outflow pathway blockages-with or without cataract surgery-ensures that ABiC has the potential to become the go-to treatment option for most types of glaucoma.
1. Battista SA, Lu Z, Hofmann S, Freddo TF, Overby DR, Gong H. Reduction of the available area for Aqueous humor outflow and increase in meshwork herniations into collector channels following acute IOP elevation in bovine eyes. Invest Ophthalmol Vis Sci. 2008;49:5346-5352.
2. Cha ED, Xu J, Gong H. Variations in active areas of aqueous humor outflow through the trabecular outflow pathway. Presented at ARVO 2015.
Mark J. Gallardo, MD
Dr. Gallardo practices at El Paso Eye Surgeons, El Paso, TX, and is adjunct clinical professor, University of Texas Health Sciences Center, San Antonio, TX. He has no financial interest in Ellex Medical Lasers Ltd.