What Is an Eye Stent and How Does It Work?

An eye stent is a tiny tube or scaffold surgically placed inside the eye to create or widen a drainage pathway for fluid, lowering the elevated eye pressure that drives glaucoma. Most eye stents belong to a category called micro-invasive glaucoma surgery, or MIGS, and they work by rerouting the eye’s internal fluid around the tissue that has become clogged. The devices are remarkably small, often just a few millimeters long, and the surgery to implant one can take only minutes, sometimes piggybacked onto routine cataract removal.

Why Eye Pressure Matters

Your eye constantly produces a clear fluid called aqueous humor. This fluid nourishes the lens and cornea, then drains out through a spongy tissue called the trabecular meshwork into a tiny channel called Schlemm’s canal, and from there into small veins. In a healthy eye, production and drainage stay balanced, keeping internal pressure stable. In glaucoma, the drainage side of that equation breaks down. About three-quarters of the resistance to fluid outflow sits within the trabecular meshwork itself, and in glaucoma that resistance climbs even higher.¹ The rising pressure gradually damages the optic nerve, stealing peripheral vision first and eventually central vision if left unchecked.

Eye drops are the first-line treatment, and they work well for many people. But drops come with daily hassles, side effects like red or irritated eyes, and a well-documented problem with adherence: people forget doses, find the bottles hard to use, or simply stop refilling prescriptions over time. Eye stents entered the picture as a way to physically bypass the blockage and reduce or eliminate the need for those daily drops.

How an Eye Stent Lowers Pressure

The basic principle is plumbing. If a pipe is clogged, you can either unclog it or route the water around the blockage. Eye stents do the latter. A trabecular stent, for example, is placed directly through the trabecular meshwork and into Schlemm’s canal, giving fluid a shortcut past the clogged tissue. Mathematical modeling shows that creating this kind of bypass raises the pressure inside Schlemm’s canal closer to the pressure inside the eye, which increases flow through the canal and its collector channels and ultimately lowers intraocular pressure.²

Other stent designs skip the natural drainage system entirely. A subconjunctival stent routes fluid from inside the eye to the space beneath the conjunctiva, the thin membrane covering the white of the eye, where it gets absorbed. A suprachoroidal stent sends fluid into the space between the wall layers of the eye. Each approach targets a different exit route, and the choice depends on how much pressure reduction a patient needs and the severity of their glaucoma.

Types of Eye Stents

The MIGS umbrella covers a range of devices, but they share a common philosophy: cause as little trauma as possible while safely and sustainably lowering eye pressure.³ Here are the main categories you will encounter.

Trabecular Bypass Stents

These are the most widely used. The iStent family (including the iStent inject W) and the Hydrus Microstent are implanted through the trabecular meshwork into Schlemm’s canal. The iStent inject W, for instance, consists of two tiny titanium stents each about 0.36 mm tall, inserted through a single corneal incision. The Hydrus is a crescent-shaped nitinol scaffold about 8 mm long that sits inside Schlemm’s canal, propping it open over a wider arc. A head-to-head comparison found that both devices significantly lowered pressure, though the Hydrus group achieved a somewhat greater relative reduction at twelve months.⁴ The iStent Infinite, a newer three-stent version designed for more severe glaucoma, has also entered clinical use.⁵

Subconjunctival Stents

The XEN 45 Gel Stent and the PRESERFLO MicroShunt take a different route, draining aqueous humor into the subconjunctival space, similar in concept to a traditional trabeculectomy but through a much smaller opening. The XEN is a 6-mm-long flexible tube made of cross-linked porcine gelatin with a 45-micrometer inner channel. The PRESERFLO MicroShunt is 8.5 mm long, made of a flexible polymer called SIBS (the same material used in some cardiac stents), and has a wider 70-micrometer channel.⁶ Both tubes are engineered so that the narrow lumen limits how fast fluid drains in the early days after surgery, reducing the risk of the eye pressure dropping too low too quickly.

Suprachoroidal Stents

These devices send fluid into the suprachoroidal space, a potential cavity between the sclera and choroid. The CyPass Micro-Stent was the most prominent device in this category, but it was voluntarily withdrawn from the market after a five-year study found increased corneal endothelial cell loss in patients who received it.⁷ A retrospective look at suprachoroidal stent outcomes found that over a third of eyes experienced sudden pressure spikes above 30 mmHg, about 39% needed additional glaucoma surgery, and the 12-month success rate was only 24%.⁸ Research into newer suprachoroidal approaches continues, including biodegradable implants designed to support the drainage pathway temporarily and then dissolve.⁹

What the Surgery Looks Like

If you are having a trabecular stent placed, the surgeon typically works through the same tiny corneal incision used for cataract surgery. You lie flat, and the surgeon uses a special lens called a gonioprism to see the drainage angle of your eye. The stent is delivered on a pre-loaded injector, clicked into place through the trabecular meshwork, and the procedure adds only a few minutes to the overall operating time. For the XEN Gel Stent, the ab interno (from inside the eye) technique is the most common approach, using a needle-tipped injector to thread the tube from the anterior chamber through the sclera and into the subconjunctival space.¹⁰ The PRESERFLO MicroShunt, by contrast, is placed from outside (ab externo), requiring a small conjunctival incision.

Recovery is generally quicker than after traditional glaucoma surgery. Most patients use anti-inflammatory drops for a few weeks and return for several follow-up visits in the first month or two. Restrictions on bending and heavy lifting are usually short-lived.

Combining Eye Stents with Cataract Surgery

This is where MIGS has found its most popular niche. Cataract surgery alone can lower eye pressure modestly by removing the thickened lens and deepening the anterior chamber, but adding a trabecular stent during the same operation can push the benefit further. In one study of patients who received a trabecular micro-bypass stent during cataract surgery, the mean pressure dropped by about 21%, and three-quarters of those who had been on one or two medications beforehand were medication-free a year later with pressures under 21 mmHg.¹¹

Combining cataract surgery with an ab interno canaloplasty and micro-trabecular bypass stent showed durable pressure reductions through three years of follow-up: pressure dropped from a baseline of about 19 mmHg to roughly 14 mmHg at both one and two years, alongside a meaningful reduction in the number of daily medications.¹² The combination is appealing because you are already undergoing one procedure, and the stent adds only minimal extra time, risk, and recovery.

For angle-closure glaucoma, the picture is a bit different. A multi-center study comparing cataract surgery with and without an iStent in patients with primary angle-closure glaucoma found that while both groups had similar pressure reductions, the stent group used fewer medications afterward. The tradeoff was a small risk of postoperative swelling of the macula or inflammation inside the eye that wasn’t seen in the cataract-surgery-only group.¹³

How Much Do Eye Drops Decrease After a Stent

Reducing the daily eye-drop burden is one of the main selling points of MIGS, and the data here are fairly consistent. A large US claims-database study found that patients who had bilateral iStent implantation during cataract surgery reduced their drop use by about one medication on average, compared with about half a medication reduction for cataract surgery alone. By roughly two years after the procedure, about 74% of the stent group was using no drops at all, compared with 55% in the cataract-only group.¹⁴ For patients on heavier medication regimens, the iStent inject combined with cataract surgery has also shown significant reductions, with the average number of medications falling substantially in the months after surgery.¹⁵

Fewer drops is not just a matter of convenience. Glaucoma eye drops contain preservatives, most commonly benzalkonium chloride, that can irritate the ocular surface over years of use. Chronic dry eye, redness, and allergic reactions are common complaints. Reducing or eliminating that chemical exposure is a real quality-of-life gain, separate from whatever pressure reduction the stent achieves.

Risks and Complications

MIGS devices are generally safer than traditional glaucoma surgeries like trabeculectomy, but they are not risk-free. Complication profiles depend heavily on the type of stent.

For trabecular stents like the iStent and Hydrus, the safety record is strong. The most commonly reported issues are minor blood reflux (hyphema) in the anterior chamber and transient pressure spikes, both of which usually resolve within days. Corneal endothelial cell health is a concern worth tracking over time, especially after the CyPass withdrawal showed that a device sitting too close to the cornea can accelerate cell loss over years.⁷

For the XEN Gel Stent, a systematic review and meta-analysis found that the most common complication was low pressure (hypotony), occurring in about one in five patients. Blood in the anterior chamber occurred in roughly 14%, and temporary pressure spikes above 30 mmHg in about 13%. Stent exposure or migration were rare, each occurring in about 1% of cases.¹⁶ Occasionally, cell debris can block the XEN lumen weeks or months after surgery, a failure mode that wasn’t widely recognized until case reports drew attention to it.¹⁷

Who Is a Good Candidate

The ideal candidates for trabecular bypass stents are people with mild-to-moderate open-angle glaucoma whose target pressure is somewhere in the mid-teens, roughly 13 to 17 mmHg. The anatomy matters too: the surgeon needs to be able to see the drainage angle clearly during the operation, so a clear cornea and an open angle with good visibility are important prerequisites.¹⁸

For more advanced or rapidly worsening glaucoma that demands very low target pressures, trabecular stents alone are usually not enough. In those situations, subconjunctival filtration devices like the XEN or PRESERFLO, or traditional procedures like trabeculectomy and tube shunt surgery, remain the go-to options.¹⁹ A XEN stent can even be implanted in an eye that has already had tube shunt surgery and still needs further pressure reduction.²⁰

People with normal-tension glaucoma, where the optic nerve is damaged even at statistically normal pressures, can also benefit from MIGS. A study of MIGS combined with cataract surgery in normal-tension glaucoma patients found a modest but statistically significant pressure reduction of about 2 mmHg at two and a half years, which in these patients can be clinically meaningful.²¹

How Eye Stents Compare to Trabeculectomy

Trabeculectomy has been the gold standard surgical treatment for glaucoma for decades, and it still achieves lower absolute pressures than any current MIGS device. A three-year comparison between the XEN Gel Stent and trabeculectomy found that trabeculectomy reduced pressure by about 50% from baseline while the XEN achieved about 35%. Complete surgical success, defined as adequate pressure control without any medications, was reached in roughly 57% of trabeculectomy patients versus 27% of XEN patients at three years.²²

So why would anyone choose a stent over trabeculectomy? The trade is between raw pressure-lowering power and everything else. MIGS procedures are faster, have a gentler recovery, preserve more of the eye’s natural anatomy, and carry a lower risk of serious complications like sustained very low pressure or infection of a filtering bleb. For patients with mild-to-moderate disease who do not need pressures driven down to single digits, a stent can hit a reasonable target with far less disruption to daily life. For those who need the deepest possible pressure reduction, trabeculectomy and tube shunts remain more effective tools.

Subconjunctival stents like the PRESERFLO MicroShunt also appear to cause less surgically induced astigmatism than trabeculectomy and may preserve visual acuity better in the short term.²³ For patients who value stable vision and quick recovery, that can tip the scale.

Long-Term Durability and the Needling Question

One of the biggest open questions with eye stents is how well they hold up over years. Trabecular stents made of titanium or nitinol are physically durable and don’t degrade, but the biological environment around them can change. Scar tissue or deposits can form around any implant, and the downstream collector channels that the stent relies on may have their own limitations.

For subconjunctival stents, the main long-term challenge is scarring of the filtering bleb, the little blister of fluid that forms under the conjunctiva. When that bleb scars down, the drainage pathway narrows and pressure creeps back up. A procedure called needling, in which a surgeon passes a needle into the bleb to break up scar tissue, is frequently needed. In a study of XEN stent outcomes in normal-tension glaucoma patients, 57% of eyes required at least one needling procedure, and one eye required additional glaucoma surgery.²⁴ Needling is a quick, office-based procedure, but the frequency with which it is needed means that a XEN implant is not strictly “one and done.” The same is true of the XEN when compared to trabeculectomy: the XEN group required needling in about 48% of eyes over three years, compared to 24% in the trabeculectomy group.²²

Researchers are actively working on materials designed to reduce this scarring problem. Biodegradable implants are one avenue: the idea is that a temporary scaffold supports the drainage pathway long enough for it to mature, then the device dissolves, leaving behind a natural channel and no foreign body to provoke chronic inflammation.⁹ Another experimental approach uses a slow-degrading polymer called polycarbonate bisamide, which could take several years to fully break down while maintaining the outflow pathway.²⁵ These are still early-stage, but they signal where the field is heading.

What Eye Stents Are Made Of

The range of materials used in glaucoma implants is surprisingly wide. Titanium and nitinol (a nickel-titanium alloy with shape-memory properties) dominate the trabecular stent market. The XEN Gel Stent is made of cross-linked porcine gelatin, chosen for its flexibility and biocompatibility. The PRESERFLO MicroShunt uses SIBS, a polymer already proven in long-term cardiovascular implants. Over the years, glaucoma device engineers have also experimented with silicone, porous polyethylene, stainless steel, and even 24-carat gold.²⁶ Each material brings different trade-offs in rigidity, biocompatibility, and the body’s scarring response.

Size and geometry also matter enormously. The inner diameter of the stent tube is carefully calculated to control flow rate. Too wide, and fluid drains too fast in the early postoperative period, causing dangerously low pressure. Too narrow, and the pressure-lowering benefit may be insufficient. The XEN’s 45-micrometer lumen and the PRESERFLO’s 70-micrometer lumen represent two different design philosophies along this spectrum, each calibrated to balance efficacy against hypotony risk.

The Cost and Quality-of-Life Equation

Glaucoma is a lifelong condition, and the costs of daily medication add up over decades: not just the price of the drops but also the follow-up visits, side-effect management, and eventual need for surgery when drops stop working. A Canadian cost-effectiveness analysis found that standalone trabecular micro-bypass stents actually saved money over time compared to medication alone, with lower total healthcare costs per patient and a small but meaningful improvement in quality-adjusted life years. The stent strategy broke even and began saving money after about 3.7 years.²⁷

In an Italian analysis, combining an iStent inject with cataract surgery was cost-effective compared to cataract surgery alone, at roughly €13,000 per quality-adjusted life year gained, a figure well within thresholds most healthcare systems consider worthwhile.²⁸ These numbers will vary by country and healthcare system, but the broad pattern is consistent: for the right patient, a stent during cataract surgery is a financially reasonable investment, not a luxury add-on. The daily grind of eye drops is itself a cost, both financial and in the wear on your ocular surface, that these devices can meaningfully reduce.