Making the case for canaloplasty

Why this procedure could be a valuable adjunct to glaucoma management

By Susan H. Senft, MD, FRCOphth

Minimally invasive glaucoma surgery (MIGS), including stenting internally from the trabecular meshwork, recently came to the forefront of glaucoma treatment.

Though canaloplasty is an older treatment, it is included in this group of technologies due to recent modifications, such as the introduction and placement of a stent, rather than viscocanalostomy alone in a limited area.

OVERVIEW

How to perform the procedure

Canaloplasty appears to improve the outflow and drainage into the collector channels once the aqueous fluid percolates outward through the internal trabecular meshwork. In this procedure, a scleral dissection extends to the Canal of Schlemm. The surgeon passes a 250-μm catheter with a lumen and fiberoptic light circumferentially 360 degrees around the canal. The catheter introduces a prolene suture tied to the tip that withdraws back through the canal. Then, the surgeon cuts the suture from the catheter and tightens it over a window of Descemet’s membrane approximately 500-μm in width. Finally, the surgeon amputates the deep scleral flap and sutures down the superficial flap.

The surgeon passes a 250-μm catheter with a lumen and fiberoptic light (top right) circumferentially 360 degrees around the Canal of Schlemm.
COURTESY ELLEX MEDICAL

The procedure is contraindicated in patients with narrow, occludable angles without a peripheral iridotomy and neovascular glaucoma because vessels can obstruct the lumen of the Canal of Schlemm and block passage of the catheter.

Also, existing medical evidence augers against a second canaloplasty in the same eye, because it is felt that a second passage through the Canal of Schlemm would not add anything after previously done.

Canaloplasty vs. other treatments

Glaucoma treatment has evolved to embrace safer, less invasive treatments. Filtering operations may have lifetime risks for an infectious endophthalmitis and a high incidence of failures and complications attributed to anti-metabolites.¹ Lasers, although safer, may not reduce IOP adequately enough to control the ravages of glaucoma over time.^2,3 Some of the newer MIGS procedures, albeit less risky, lack the ability to dramatically reduce IOP beyond the earliest stages of the disease. Thus, we’ve searched for safe, non-invasive yet effective treatments to change how we treat glaucoma.

How it works

Canaloplasty success seems to result from a multivariate approach, with each aspect of the procedure requiring attention to detail. Creating the Descemet’s window and its subsequent “lake” is perhaps as key as the placement of a stent, because cases with a 500-μm Descemet’s window appear to work well without the stent.

We occasionally encounter obstructions during catheter passage. Passing it completely around the eye, much less leaving a stent behind, is not always possible in some eyes. Again, data have shown the stent is not the entire rate-limiting factor; retrospective data where one eye received a stent and the fellow eye did not have shown the postoperative parameters appeared to demonstrate no statistical difference. Rather, it appears that cannulating the Canal of Schlemm to permit the collector channels to function again appears integral to a successful canaloplasty.

In addition, viscodilation seems to awaken the collapsed collector channels. Rather than dilate just a few clock hours upon catheter removal, this aspect of the procedure involves injecting some viscoelastic roughly every two clock hours and utilizing a viscoelastic bolus to ease through resistance or blockage of the canal when passing the catheter.⁷

Studying outcomes

Canaloplasty is a relatively safe, unique niche that does not rely on a filtering bleb and its associated problems, such as a failed, scarred bleb or, rarely, an endophthalmitis.^4,5

A retrospective study of canaloplasty involved patients not only in early phases of glaucoma, but throughout the spectrum of the disease, including a series of patients who had other failed glaucoma procedures, such as ALT, SLT, filtering blebs with mitomycin-C, aqueous shunts and various combinations of the preceding.

The study aimed to evaluate whether scarring after previous glaucoma surgeries precluded canaloplasty. Parameters involved monitoring visual acuity, visual fields, IOP and medication use.⁶ One challenge was to evaluate whether stent placement was even possible in this group and determine whether successful outcomes were dependent upon stent placement.

Results on this small series of 25 eyes followed over 2.5 years indicated approximately 60% of eyes had stents placed with no affect on outcomes. Medications use was reduced in 57% and eliminated entirely in 33%, and 10% were taking the same number of medications after surgery as before.

FUTURE APPLICATIONS

Potential option in children

Because of its safety profile, canaloplasty appears to present an option in juvenile glaucoma group in lieu of aqueous shunting and failed filtering blebs. For example, several children ages 10 to 12 had impressive outcomes over 1.5 years after the procedure, according to personal data. In one such case, an IOP of 50 mm Hg on no medications was controlled to the mid-20s on medications not tolerated due to side effects and progressed to a sustainable IOP of 10 mm Hg without any medications. In addition, large groups of children are undergoing the procedure with one highly effective modification: the Canal of Schlemm sustains a 360-degree trabeculotomy instead of leaving a prolene stent behind.

Future modifications of the techniques in ways not realized at present may enable more widespread adoption.

BARRIERS TO WIDESPREAD ADOPTION

Difficult to learn

Canaloplasty can be safe and effective with minimal risk in patients from childhood through late adulthood. So, the question remains: Why is it not more commonly adopted in the glaucoma patient population?

Several reasons are readily apparent. Previously, the learning curve was thought to be onerous for some who used trabeculectomy knives and instrumentation. This made the deep flap creation challenging since they were too large and did not allow a meticulous and delicate dissection of the surgical plane. However, the learning curve has shortened thanks to the development of specialized knives for dissection along with patience and persistence for mastering the techniques of dissection and understanding the landmarks for finding the Canal of Schlemm.

Misconceptions

Accepting that failure to cannulate the canal 360 degrees does not constitute overall failure nor require conversion to a filtering operation seems to be of great benefit, because one would not have to convert the operation to a trabeculectomy. This procedure could be combined with cataract extraction at the same setting or as a stand-alone procedure. Often, combining the two procedures results in lowered IOP, because any effect of narrowing of the anterior chamber due to the crystalline lens would be remedied by lens removal and replacement with an intraocular lens.

Exposure of the Descemet’s window. Creation of the window and its subsequent “lake” is a key step in the canaloplasty procedure.
COURTESY ELLEX MEDICAL

Time was felt to be another barrier to wide acceptance. In the past, the procedure’s time length approached nearly an hour or more and was not felt to be cost-effective in a surgery-center setting with reimbursement levels. Currently, surgeons familiar with the procedure can perform all steps in 20 to 30 minutes and have a successful, long-lasting outcome with IOP ranging from single digits to averaging between 12-13 mm Hg on no medications.

PATIENT BENEFITS

Reducing financial and personal repercussions

Controlling, if not outright curing, a chronic disease like glaucoma is priceless. Also, in some regions of the world, it has been estimated that 10 family members and friends are needed to assist each blind individual through life, showing the repercussions to society associated with needless blindness.

Meanwhile, medication costs add up over time, and related problems, such as intolerance and allergies, can lead to compliance issues and the inability to afford new advances in medications. It all adds up.

Removing the variable of chronic medication use cannot help but improve outcomes. As the population ages and dementia becomes more prevalent, this aspect also becomes significant. For instance, if an Alzheimer’s patient successfully controls her or his drop regimen but sporadically or never remembers to administer these medications, that is tantamount to not using any medications.

Minimally invasive and maximally effective

Canaloplasty, either alone or in conjunction with cataract extraction, has a definite role in glaucoma management. It could be considered an aspect of MIGS, although, unlike some of those procedures, canaloplasty appears to be minimally invasive and maximally effective across the entire spectrum of the disease — from early manifestation to advanced vision loss.

Canaloplasty appears effective in patients who have had previous failed glaucoma procedures, and it presents a viable alternative to traditional aqueous shunts and filtering operations in juvenile glaucoma. As more ophthalmologists and their patients embrace the technology, we can gather more data and find more indications for this novel technique.

With our armamentarium at hand and new developments ahead, the challenges of glaucoma may be controllable and even curable. OM

REFERENCES

About the Author

Susan H. Senft, MD, FRCOphth, is a comprehensive ophthalmologist and founder of Island Eye Care, Inc. in Kailua-Kona, Hawaii. She is fellowship trained in anterior segment, pediatric ophthalmology and strabismus and oculoplastics and has performed canaloplasty since 2012. Her e-mail is senft808@gmail.com. Disclosure: Dr. Senft is an advisor of Ellex International, manufacturer of iScience catheter products.