Canaloplasty is a surgical procedure for glaucoma that lowers eye pressure by reopening the eye’s natural drainage channel, called Schlemm’s canal. Unlike more traditional glaucoma surgeries that create a new drainage pathway, canaloplasty restores the one your eye already has. It’s primarily used for open-angle glaucoma, the most common form of the disease, and typically reduces eye pressure by about 30% over the long term.
How the Eye’s Drainage System Works
Your eye constantly produces a clear fluid called aqueous humor that nourishes internal structures and maintains the eye’s shape. This fluid drains out through a mesh-like tissue (the trabecular meshwork) into a tiny circular channel called Schlemm’s canal, which wraps around the entire iris like a ring. From there, the fluid flows into small veins and leaves the eye.
In open-angle glaucoma, this drainage pathway becomes sluggish. Fluid builds up, pressure rises, and over time the optic nerve gets damaged. Canaloplasty targets this problem at its source by physically widening Schlemm’s canal and improving flow through the meshwork.
What Happens During the Procedure
The traditional version, called ab-externo canaloplasty, is performed from the outside of the eye under local anesthesia. The surgeon creates a small flap in the white outer wall of the eye (the sclera) to access Schlemm’s canal directly. A second, deeper flap is then carved to expose the canal’s opening.
Once the canal is reached, a tiny flexible catheter with a glowing tip is threaded all the way around it, completing a full 360-degree loop. As the catheter travels through, it delivers a gel-like substance that stretches the canal open. When the catheter is pulled back out, it leaves behind a fine suture thread looped through the entire channel. This suture is tied with just enough tension to keep the inner wall of the drainage meshwork pulled inward, permanently holding the canal in a widened position. The outer flap is then stitched closed tightly to prevent any fluid from pooling on the surface of the eye.
Ab-Interno Canaloplasty: A Less Invasive Option
A newer variation called ab-interno canaloplasty (ABiC) performs the same canal-widening step but from inside the eye. Instead of cutting through the outer wall, the surgeon enters through a tiny corneal incision and threads the catheter into Schlemm’s canal using a special lens to see the drainage angle. The catheter delivers the same stretching gel as it’s withdrawn.
The key difference is that ABiC skips the scleral flap entirely, leaves no tensioning suture in the canal, and doesn’t disturb the conjunctiva (the clear tissue covering the white of the eye). This matters because preserving the conjunctiva keeps future surgical options open if additional glaucoma procedures are ever needed. ABiC is also technically simpler for surgeons, since the traditional approach requires precise flap dissection and careful suture tensioning that can be challenging to master.
Both versions produce temporary microhyphema, a small amount of blood in the front of the eye, that typically clears within about a week.
How Well It Lowers Eye Pressure
At 12 months, canaloplasty reduces average eye pressure from about 24 mmHg to roughly 15 mmHg. Patients also go from using an average of 2.3 pressure-lowering eye drops daily down to 0.6. These results hold up over time. A ten-year study found sustained pressure reductions of approximately 30%, with readings staying around 15 to 16 mmHg at the one, five, and ten-year marks.
The procedure works best when starting pressure is moderate. Patients with preoperative pressures at or below about 27 mmHg are most likely to reach a target of 18 mmHg or lower without needing any eye drops afterward. Those with pressures up to around 37 mmHg can still benefit but may need to continue using drops.
About 11 to 19% of patients require a reoperation, mostly within the first five years. People with a specific subtype called pseudoexfoliation glaucoma face a significantly higher risk of needing additional surgery compared to those with primary open-angle glaucoma.
Common Risks and Complications
The most frequent complication is hyphema, blood collecting in the front chamber of the eye. In one large study, this occurred in 55% of cases, though it’s generally mild and resolves on its own. A small number of patients (about 2%) experience a detachment of a thin membrane inside the eye called Descemet’s membrane. Temporary pressure spikes can also occur in the early postoperative period, sometimes requiring a minor laser procedure called goniopuncture to relieve the pressure. In that same study, about 14% of patients needed this follow-up within the first three months.
How It Compares to Trabeculectomy
Trabeculectomy, the traditional gold-standard glaucoma surgery, creates an entirely new drainage pathway by cutting a small hole through the eye wall and forming a fluid-collecting blister (called a bleb) under the eyelid. It achieves slightly lower eye pressures than canaloplasty at 12 months, roughly 2 mmHg lower on average.
The tradeoff is a heavier complication profile. Trabeculectomy carries a meaningfully higher risk of dangerously low eye pressure (hypotony) and abnormal fluid collections behind the eye (choroidal detachments). Canaloplasty patients are about three times more likely to get hyphema, but this is a milder and self-resolving issue by comparison. Trabeculectomy also demands more intensive postoperative care, with frequent visits for bleb management and potential interventions to keep the drainage site functioning. Canaloplasty avoids bleb formation entirely, which simplifies recovery and eliminates the lifelong risk of bleb-related infections.
Who Is a Good Candidate
Canaloplasty is designed for open-angle glaucoma, where the drainage angle between the iris and cornea remains physically open but isn’t functioning well. It works for both primary open-angle glaucoma and pseudoexfoliation glaucoma, though the latter has higher reoperation rates. People whose pressure is in the moderate range and who want to reduce their dependence on daily eye drops tend to see the most benefit.
The procedure is not suitable for angle-closure glaucoma, where the iris physically blocks drainage. It also relies on the structural integrity of Schlemm’s canal, so eyes with significant scarring or previous surgeries that disrupted the canal may not be candidates. Because the ab-externo version requires precise dissection of the sclera, eyes with very thin or abnormal scleral tissue can pose challenges.
Recovery After Canaloplasty
Vision recovery is relatively quick, particularly with the ab-interno approach. Many patients notice their vision returning to baseline within days, and because the procedure uses small incisions and preserves the eye’s overall shape, discomfort is generally mild. Follow-up visits are typically scheduled the day after surgery, then every one to three weeks for the first two to three months as the eye heals.
Your eye drop regimen will change after surgery. Some or all of your glaucoma drops may be stopped, while short-term anti-inflammatory or antibiotic drops are usually prescribed to support healing. Your surgeon will adjust your medications based on how your pressure responds in the weeks following the procedure.
During recovery, you should avoid heavy lifting (generally nothing over 10 pounds), bending at the waist, vigorous exercise, and any straining that raises pressure in the head. Gentle walking is fine for most people. Once eye pressure stabilizes, light work duties can typically resume within one to two weeks. More strenuous activities are gradually reintroduced based on your surgeon’s assessment at follow-up visits.