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Ab-interno canaloplasty (ABiC) is a minimally invasive glaucoma surgery that accesses, catheterizes, and viscodilates all sites controlling aqueous outflow. When performed alone for uncontrolled glaucoma or with cataract surgery, it can result in reduced IOP and daily medication at follow-up through 12 months.
Reviewed by Mark Gallardo, MD
El Paso, TX-Growing experience with ab-interno canaloplasty (ABiC) shows the minimally invasive glaucoma surgery (MIGS) is very safe and provides significant and sustained reduction of IOP and medication use, according to Mark Gallardo, MD.
Performed through a 1.8-mm, temporal clear-corneal incision and using an illuminated microcatheter (iTrack 250A, Ellex) that provides continual transscleral visualization, ABiC lowers IOP by restoring the natural pathway of aqueous outflow.
Based on its outcomes and benefits, Dr. Gallardo said he now considers ABiC as a first-line option for patients with mild-to-moderate glaucoma whose IOP is uncontrolled on maximum tolerated medical therapy.
Because of its potential to reduce or eliminate medication burden, he also sees ABiC as a useful adjunct when performing cataract surgery in patients with mild-to-moderate glaucoma controlled on medications.
Dr. Gallardo is in private practice, El Paso Eye Surgeons, El Paso, TX, and an adjunct clinical faculty member in the department of ophthalmology at University of Texas Health Science Center, San Antonio, and Texas Tech Health Sciences Center, Lubbock.
With passage of the microcatheter through the ostomy in the trabecular meshwork, ABiC uniquely accesses, catheterizes, and viscodilates all sites controlling aqueous outflow. It has been associated with an average IOP reduction of about 35%, and with follow-up available to 18 months in some patients, its benefit is largely maintained, he noted.
“What I love most about ABiC, however, is that it is truly an atraumatic procedure,” Dr. Gallardo said.
“With the exception of the small otomy created in the trabecular meshwork, there is no disruption of tissue throughout the aqueous drainage system,” he said. “Therefore, ABiC has an excellent safety profile-no sight-threatening complications have been associated with its use, and other surgical options remain available if ABiC is not successful or fails over time.”
The idea for ABiC stems from evidence that good IOP lowering was still achieved in eyes that underwent traditional canaloplasty without placement of the tensioning suture.
“To date, I have a number of patients who had traditional canaloplasty in one eye and then ABiC in the other whose IOP and need for medication is similar in their fellow eyes,” Dr. Gallardo said.
ABiC can achieve the same outcome as traditional canaloplasty, but it is a much simpler and faster surgery because it eliminates the major incisional steps of the ab externo approach and placement of a tensioning suture, he noted.
Dr. Gallardo has analyzed results for his patients who have up to 12 months of follow-up. Mean IOP in this cohort was reduced from 18.6 ± 6.4 mm Hg preoperatively (n = 122) to 14.1 ± 3.7 mm Hg at 6 months (n = 65) and to 12.9 ±2.0 mm Hg at 12 months (n = 28). Mean number of medications used daily was reduced by half from 2.0 to 1.0.
Courtesy of Mark Gallardo, MDAbout 50%of the patients in his series underwent ABiC alone. In that subgroup, mean IOP was reduced from 21.3 ± 7.4 mm Hg at baseline to 13.3 ±2.3 mm Hg at 12 months with a 66% reduction in mean daily medication use.
“ABiC is also distinguished from other MIGS procedures by the fact that it is the only one approved to be performed as a standalone operation,” Dr. Gallardo said. “Whether it is performed as a single procedure or in combination with cataract surgery, the results are excellent.”
A pooled analysis of data including 106 eyes operated on by Mahmoud A. Khaimi, MD, clinical associate professor of ophthalmology, Dean McGee Eye Institute, University of Oklahoma College of Medicine, Oklahoma City, shows that among patients who had combination cataract and ABiC surgery, IOP was reduced from a baseline mean of 17.1 ± 5.0 mm Hg to 13.1 ± 2.1 mm Hg at 12 months with a 50% decrease in daily medication requirement.
Other subgroup analyses in the combined cohort included 161 patients classified has having uncontrolled glaucoma (IOP ≥16 mm Hg), 73 patients with uncontrolled glaucoma on maximum medical therapy, and a small number with a history of selective laser trabecuoplasty.
Across all of those subgroups, mean IOP was reduced by about 40% and patients were able to reduce their medication use by at least half. Among 67 patients with controlled glaucoma (baseline IOP ≤15 mm Hg, mean 12.9 mm Hg), average daily medication use was reduced from 2.0 ± 1.0 to 0.0 ± 1.0 at 6 (n = 44) and 12 months (n = 17).
Dr. Gallardo acknowledged that ABiC, like all MIGS procedures, is not a replacement for trabeculectomy, but he pointed out that not all patients need a filtering procedure for reaching their target IOP.
Approaches to the management of coronary artery disease (CAD) offers a good analogy, he said.
“When possible, patients needing surgical intervention for CAD will be treated with a minimally invasive approach using cardiac catheterization with a stent or balloon angioplasty rather than undergoing a coronary artery bypass procedure,” he said.
The same premise applies to glaucoma surgery, he noted.
“Trying ABiC first to rejuvenate the natural drainage system in appropriately selected patients is a minimally invasive procedure that can be very successful but leaves the opportunity to perform a procedure that bypasses the natural drainage system if it is unsuccessful,” Dr. Gallardo said.
Although the population of patients eligible for ABiC is broad, there are certain exclusions. As with traditional canaloplasty, patients with neovascular, chronic angle closure, steroid-induced or narrow-angle glaucoma, as well as those with angle recession or peripheral anterior synechiae are not considered candidates for ABiC, he added.
Surgeons who have not yet adopted any form of surgery targeting Schlemm’s canal should expect to face a learning curve in order to become accustomed to working in the angle, obtaining proper visualization with a gonioprism, and manipulating the microinvasive instruments in that tight surgical space.
However, Dr. Gallardo suggested that it behooves surgeons who are not performing canal-based procedures to move into that realm as it likely represents the future of glaucoma surgery.
“Most of the MIGS procedures in development involve working with the anatomy of the outflow system and involve use of a gonioprism,” he said. “I anticipate that they will eventually become standard of care as first-line intervention before more invasive filtering procedures.”
Mark Gallardo, MD
Dr. Gallardo is a paid consultant, speaker, and principal investigator of ABiC for Ellex.