iStent for Glaucoma: How It Lowers Eye Pressure

The iStent is a tiny implantable device used to lower eye pressure in people with open-angle glaucoma, and it holds the distinction of being the first minimally invasive glaucoma surgery (MIGS) device approved by the FDA. It works by creating a permanent shortcut for fluid to drain out of the eye, bypassing the clogged drainage tissue that causes pressure to build up. Over multiple generations of design refinements and more than a decade of clinical data, the iStent has become one of the most widely studied MIGS options, though where it fits in the broader landscape of glaucoma treatment depends on factors like disease severity, whether cataract surgery is already planned, and how many eye drops a patient is willing to keep using.

How the iStent Lowers Eye Pressure

In a healthy eye, a clear fluid called aqueous humor flows through a spongy drainage tissue called the trabecular meshwork and into a circular channel called Schlemm’s canal, which feeds into veins that carry the fluid away. In open-angle glaucoma, resistance builds up in that trabecular meshwork, so fluid backs up and pressure rises. The iStent is a microscopic tube that gets implanted directly through the trabecular meshwork, creating a direct channel between the front chamber of the eye and Schlemm’s canal.¹ Think of it like punching a hole through a clogged filter so fluid can pass freely to the other side.

Because the device restores drainage through the eye’s natural outflow pathway rather than creating an entirely new one (the way traditional glaucoma surgeries like trabeculectomy do), the procedure carries a fundamentally different risk profile. There is no bleb, no external wound to manage, and the surgery itself is performed from inside the eye through the same incision used for cataract removal. That internal approach is why you will often see the iStent described as an “ab interno” procedure.

Three Generations of the Device

The original iStent was a single L-shaped titanium stent about 1 mm long. It was typically implanted one at a time, though surgeons sometimes placed two or three to access more of Schlemm’s canal. The second-generation device, the iStent inject, changed the concept: it came preloaded with two tiny stents in a single injector, each just 360 micrometers tall with a 230-micrometer base. The idea was to open two separate segments of Schlemm’s canal in one pass.

The third generation, the iStent inject W, kept the same height but widened the base to 360 micrometers. That might sound like a trivial dimensional change, but a head-to-head comparison found it made a meaningful difference in positioning. At six months after surgery, the iStent inject W group saw a larger pressure drop than the earlier iStent inject group, and the researchers attributed this to better stent placement enabled by the wider base.² Most recently, the iStent infinite was introduced for more advanced glaucoma, featuring three stents preloaded in a single injector and approved as a standalone procedure without requiring concurrent cataract surgery.

How Well It Works for Pressure Reduction

The clearest picture of iStent efficacy comes from studies that look at the device used on its own, without the confounding pressure-lowering effect of cataract removal. A systematic review and meta-analysis of standalone iStent studies found a weighted average pressure reduction of about 31% at six to twelve months after implantation, translating to roughly 7 mmHg off the baseline. That benefit held up remarkably well over time: at three to five years, the weighted average reduction was still around 30 to 33%.³

A seven-year prospective study of the iStent inject confirmed that durability. Across the full cohort, pressure dropped by 36 to 40% over the follow-up period, with roughly 84% of eyes maintaining at least a 20% pressure reduction at their last visit.⁴ Eyes that received the iStent inject as a standalone procedure actually did slightly better than those that had it combined with cataract surgery, which may reflect case selection differences more than a true advantage.

When you look at the iStent combined with cataract surgery and compare it to cataract surgery alone, real-world registry data from more than a thousand eyes showed that about 41% of iStent eyes achieved a greater than 20% pressure reduction at twelve months, compared with 30% in the cataract-only group. The iStent group also needed fewer secondary pressure-lowering procedures afterward.⁵ A randomized controlled trial, however, tells a more nuanced story: while the iStent group used significantly fewer medications at two years, the difference in actual pressure readings between the two groups was not significant beyond the first month.⁶ The take-home is that when combined with cataract surgery, the iStent’s biggest consistent benefit may be freeing patients from eye drops rather than dramatically lowering pressure beyond what cataract surgery itself achieves.

The Eye Drop Question

For many glaucoma patients, the daily burden of eye drops is the most frustrating part of the disease. Drops sting, cause red eyes, can discolor the skin around the lids, and are easy to forget. A major part of the iStent’s appeal is reducing or eliminating that medication load.

The seven-year iStent inject data showed medication use dropped by 59 to 71% across the full cohort, with standalone eyes seeing reductions of 62 to 76%.⁷ A five-year prospective study of two first-generation iStents placed as a standalone procedure found that roughly 90% of eyes remained completely medication-free through the entire follow-up period.⁸ That is a striking number, though it came from a carefully selected group of patients with mild to moderate disease.

When the iStent is paired with cataract surgery, a real-world community-practice study of the iStent inject W found that the percentage of patients needing no pressure-lowering drops rose from 16% before surgery to 24% at twelve months, while patients who had been on three medications preoperatively were cut in half.⁹ Those real-world numbers are more modest than the prospective trial results, which makes sense: community-based patients tend to have more variable disease severity and follow-up compliance.

An earlier meta-analysis focused specifically on the solo iStent procedure found that two stents implanted together produced the largest pressure drop, though even a single stent reduced medication use by about 1.2 bottles per patient at eighteen months.¹⁰ Going from three daily drops to one or two may not sound dramatic in the abstract, but for someone who has been battling adherence for years, it can meaningfully change daily quality of life.

Long-Term Durability

One of the persistent questions with any implanted device is whether the benefit holds or slowly fades. The longest published data for the iStent now extends to eight years. In a study following patients who received two first-generation iStents combined with cataract surgery, pressure was reduced by 26% at eight years, with over 90% of eyes maintaining pressure at or below 18 mmHg. Medication use decreased modestly, by about 18% from preoperative levels, and the surgical success rate (meaning no additional glaucoma surgery was needed) was 90%.¹¹

A separate five-year trial compared two iStents used as a standalone procedure against the prostaglandin eye drop travoprost. Both groups achieved similar pressure reductions of about 35%, but the stent group had a clear advantage in independence from medication: only 17% of stent eyes needed add-on drops at five years, compared with 44% of the travoprost eyes. Treatment success, defined as pressure between 6 and 18 mmHg without additional medication or surgery, was significantly higher in the stent group at 77% versus 53%.¹² The Manchester iStent study, following patients out to seven years (84 months), reported a mean absolute reduction of about 4.9 mmHg and a drop of about 0.6 medications from preoperative levels at that final time point.¹³

Safety and Complications

The iStent is broadly considered one of the safest glaucoma procedures available, but “safe” does not mean “zero risk.” A meta-analysis pooling data from 27 studies found that about 22.5% of iStent-implanted eyes experienced some type of adverse event.¹⁴ That number sounds high, but the most common events were transient and self-resolving:

Pressure spikes: A temporary rise in eye pressure in the early postoperative period, reported in nearly half the studies. These typically resolve within days.
Stent obstruction: Blockage of the stent lumen, reported in about 30% of studies. This can sometimes be addressed with a follow-up laser procedure.
Malposition: The stent not sitting where the surgeon intended, reported in about a quarter of studies. A mispositioned stent may still function partially or can sometimes be repositioned.
Hyphema: A small collection of blood in the front of the eye, reported in about 22% of studies. This is usually a sign that the stent has successfully opened Schlemm’s canal (blood refluxes back from the canal) and clears on its own.

Serious complications like persistent low pressure (hypotony) or significant vision loss were rare. No cases required device removal in most series. For context, traditional glaucoma surgery (trabeculectomy) carries much higher rates of serious complications including infection of the filtering bleb, dangerously low pressure, and vision-threatening scarring.

Does the iStent Damage the Cornea?

Because the iStent sits inside the eye near the cornea, there has been understandable concern about whether it slowly damages the corneal endothelium, the delicate single-cell layer on the inner surface of the cornea that keeps it clear. Losing too many of these cells leads to permanent corneal swelling and cloudy vision, and the cells do not regenerate.

The reassuring answer from multiple studies is that the iStent does not appear to accelerate corneal cell loss beyond what cataract surgery alone causes. A controlled study found no significant difference in endothelial cell loss between iStent-plus-cataract-surgery eyes and cataract-surgery-alone eyes at 18 to 24 months.¹⁵ Longer-term data from a five-year study of the iStent inject confirmed this: the average annual rate of endothelial cell loss was about 19 cells per square millimeter in the iStent group versus about 22 cells per square millimeter in the control group, a difference that was neither clinically nor statistically meaningful.¹⁶ Earlier studies had reported cell loss rates ranging from about 2.5% to 13% after iStent implantation combined with cataract surgery, but the absence of proper control groups in some of those studies made it hard to separate the iStent’s effect from the effect of the cataract surgery itself.¹⁷

How the iStent Compares With Other MIGS Devices

The iStent is not the only MIGS game in town. Two of its most common comparators are the Hydrus Microstent (a scaffold that opens a longer stretch of Schlemm’s canal) and the Kahook Dual Blade (KDB), a disposable instrument that excises a strip of trabecular meshwork rather than implanting anything at all.

Head-to-head data between the Hydrus and iStent inject are remarkably similar. A propensity-matched study at twelve months found no significant difference in pressure lowering between the two devices.¹⁸ Long-term data extending to four years echoed that finding: surgical success rates were essentially identical at 43% for iStent versus 41% for Hydrus, with similar pressure reductions, medication reductions, and adverse event rates.¹⁹

The comparison with Kahook Dual Blade is more interesting. A twelve-month retrospective study found that KDB combined with cataract surgery produced significantly greater pressure reductions than the iStent at every time point, with 64% of KDB eyes achieving a 20% or greater pressure reduction versus 42% for iStent eyes.²⁰ A longer follow-up study through five years, however, found no significant difference in pressure reduction between the two approaches over time. KDB did maintain an advantage in medication reduction at all time points and had a lower rate of secondary procedures, though neither difference reached statistical significance at the five-year mark.²¹ A two-year comparison similarly showed equivalent pressure lowering but a greater reduction in medication count with KDB.²²

The practical takeaway is that among canal-based MIGS procedures, the differences in pressure-lowering ability are relatively small. The choice often comes down to surgeon familiarity, whether you want a permanent implant left in the eye (iStent) or not (KDB), and the patient’s specific anatomy.

What About Normal-Tension and Secondary Glaucoma?

Most iStent research focuses on primary open-angle glaucoma where baseline pressures are elevated, but the device has also been studied in situations where pressure is technically “normal” yet still damaging the optic nerve. A meta-analysis of angle-based MIGS in normal-tension glaucoma found that the iStent inject combined with cataract surgery produced a pressure reduction of about 2.3 mmHg and a drop of about one medication at twelve months.²³ A couple of mmHg may sound negligible, but in normal-tension glaucoma every small reduction matters, and the real value may again lie in shedding medications that cause ocular surface irritation.

For secondary forms of open-angle glaucoma, including glaucoma caused by eye trauma, steroid use, or pseudoexfoliation, a small prospective case series found that a single iStent reduced pressure by about 6.6 mmHg and cut medication use by about one drop at twelve months, with no serious safety concerns.²⁴ The evidence base here is thin, though, and clinicians tend to be more cautious about MIGS in secondary glaucomas where the drainage anatomy may be structurally abnormal.

Cost-Effectiveness

Adding any device to a surgery raises costs, so the question of whether the iStent is worth the extra expense is a fair one. Health-economic modeling from France calculated that adding the iStent inject to cataract surgery cost only about €75 more per patient over a lifetime horizon, because nearly all of the device’s upfront cost was offset by savings from fewer medications, fewer follow-up visits, and fewer secondary surgeries. The cost per quality-adjusted life year gained was about €1,154, well below common willingness-to-pay thresholds.²⁵

A Japanese cost-utility analysis reached a similar conclusion, finding the combination cost-effective at roughly ¥1.4 million per QALY gained. When the model incorporated the burden placed on caregivers of patients who progress to blindness, the iStent-plus-cataract combination actually dominated cataract surgery alone, meaning it was both more effective and cheaper from a societal perspective.²⁶ These analyses depend heavily on modeling assumptions, but the consistent finding across different healthcare systems is that the device pays for itself in reduced downstream costs.

Patient Satisfaction and Recovery

Because the iStent is inserted through the same incision used for cataract surgery, recovery is essentially the same as cataract surgery alone. A study that used a glaucoma-specific patient-reported outcome measure found that about 74% of patients were “quite satisfied” or “very satisfied” with their surgical outcome after iStent inject combined with cataract surgery. Adverse events perceived by patients were minimal: 97% reported no complications and no pain or discomfort at all. Satisfaction did not differ between patients with mild versus moderate glaucoma, and 97% rated their post-surgical quality of life as “good” or “very good.”²⁷

The surgical learning curve is also worth noting if you are considering having the procedure done at a teaching hospital. A study tracking trainee surgeons found that the first cases took an average of about 35 minutes, but operative time dropped by roughly 8.5 minutes as surgeons gained experience. The most common intraoperative event was minor bleeding from the trabecular meshwork, which is expected and not harmful, and no complications required a return to the operating room.²⁸

Combining the iStent With Sustained-Release Drug Implants

One of the newer frontiers in glaucoma management is pairing a MIGS device like the iStent with a sustained-release drug implant that slowly delivers medication inside the eye, potentially eliminating the need for drops altogether. Early real-world data on combining the three-stent iStent infinite with the iDose TR travoprost implant (an intracameral slow-release device) looked promising: at three months, pressure dropped by about 4.7 mmHg and the topical medication burden fell from about two drops to fewer than one, with no serious complications reported in any of the 33 eyes studied.²⁹

A broader look at combining the travoprost implant with various MIGS procedures, including the iStent infinite and canaloplasty, confirmed significant reductions in both pressure and medication use across most subgroups.³⁰ This multimodal approach, attacking both the drainage pathway and the fluid-production side in a single sitting, represents a shift toward treating glaucoma more like an interventional problem and less like a chronic medication-management exercise. The data are still early, and long-term follow-up will determine whether combining devices holds its benefit or introduces unforeseen interactions, but it is a space worth watching.

Imaging and Stent Positioning

One challenge with any trabecular micro-bypass is confirming that the stent ended up in the right spot and is actually functioning. Standard clinical exams using gonioscopy can verify that the stent is visible in the angle, but they cannot reveal subtle details about orientation or whether the stent is truly engaging Schlemm’s canal effectively. Researchers have developed specialized optical coherence tomography (OCT) techniques that can resolve the three-dimensional position of the iStent inside the eye and even measure how much the surrounding trabecular meshwork is moving in response to the implant. One such study found that tissue displacement was significantly greater in regions between two iStents compared with areas farther away, providing direct physical evidence that the stents alter local fluid dynamics.³¹ These imaging tools are still research instruments rather than clinical standards, but they point toward a future where surgeons can verify and potentially optimize stent function after placement, rather than relying solely on pressure readings to judge success.