Glaucoma stent surgery carries a lower overall complication rate than traditional filtering surgery, but it is not risk-free. The most frequent side effect across stent types is a temporary drop in eye pressure below normal levels, a condition called hypotony, which affects anywhere from roughly 15 to 57 percent of patients depending on the device and how hypotony is defined. Beyond that headline number, the procedure brings a distinct set of risks that range from pressure spikes and stent blockage to scarring that can undo the surgery’s benefits over time. Understanding these complications helps you weigh the trade-offs before consenting and recognize warning signs during recovery.
Hypotony Is the Most Common Early Complication
When a stent creates a new drainage pathway for fluid inside the eye, the pressure can temporarily fall too low. This low-pressure state, called hypotony, is the single most reported complication of gel stent procedures. A systematic review and meta-analysis of the XEN45 gel stent found that about one in five patients experienced numerical hypotony after surgery, though individual studies report rates as high as two in three patients depending on the threshold used and the follow-up window.1PubMed Central. Complications and post-operative interventions in XEN45 gel stent implantation in the treatment of open angle glaucoma—a systematic review and meta-analysis Another analysis of the XEN63, a wider-bore version, placed the hypotony rate between 18 and 66 percent.2AJO International. State of the art, advantages and drawbacks of XEN 63 gel stent in glaucoma surgery
The good news is that most hypotony resolves without lasting harm. One study found that in eyes where pressure fell to 6 mmHg or below after XEN implantation, about 70 percent had no complications at all. Another 13 percent experienced transient issues that resolved on their own. Only about 17 percent needed treatment for hypotony-related problems such as fluid collecting behind the retina (choroidal detachment) or a shallow front chamber of the eye.3PubMed Central. Risk factors for ocular hypotony after XEN Gel Stent implantation That same study identified two factors that shifted the odds: eyes with longer axial length (often seen in people who are very nearsighted) had about three times the risk of hypotony, while having cataract surgery performed at the same time roughly halved the risk.3PubMed Central. Risk factors for ocular hypotony after XEN Gel Stent implantation
Bleeding Inside the Eye
Some blood in the front chamber of the eye, known as hyphema, is the second most common early complication after gel stent placement. The meta-analysis of XEN45 studies placed the rate of noticeable hyphema at about 14 percent.1PubMed Central. Complications and post-operative interventions in XEN45 gel stent implantation in the treatment of open angle glaucoma—a systematic review and meta-analysis In most cases the blood clears on its own within days. The concern is less about the bleeding itself and more about what it can cause downstream: a blood clot can block the stent’s tiny internal channel, which leads to a different complication discussed below.
Stent Blockage and Displacement
The internal channel of a gel stent is extremely narrow, which makes it vulnerable to obstruction. A systematic review found that stent blockage occurs in roughly 4 to 9 percent of cases. The culprit can be a blood clot, a strand of fibrous tissue, or even the iris drifting into the opening.4PubMed Central. Complications of XEN gel stent implantation for the treatment of glaucoma: a systematic review Clearing the blockage depends on what caused it. If the iris is the problem, a brief laser procedure can push it away. Clots or fibrin plugs can sometimes be dissolved with an injection of a clot-busting drug, or broken up with a laser. In stubborn cases, surgical instruments or even a fine nylon suture threaded through the lumen are used to reopen the channel.4PubMed Central. Complications of XEN gel stent implantation for the treatment of glaucoma: a systematic review
A rarer but more dramatic problem is stent migration, where the device shifts out of its intended position. Proper placement leaves about 1 mm of the stent visible inside the front chamber of the eye, roughly 2 mm tucked within the sclera, and about 3 mm exiting under the conjunctiva. If too much of the stent sits inside the eye with too little anchored externally, external forces like blinking can nudge it loose over time.4PubMed Central. Complications of XEN gel stent implantation for the treatment of glaucoma: a systematic review At least one published case documented a XEN implant that worked well for four months before migrating entirely into the front chamber, requiring the patient to restart eye-pressure drops.5PubMed Central. Dislocation of a previously successful XEN glaucoma implant into the anterior chamber: a case report
Pressure Spikes After Surgery
While hypotony gets the most attention, the opposite problem also occurs. After iStent inject placement combined with cataract surgery, one study found that more than 13 percent of patients had a pressure spike exceeding 30 percent above their baseline at the one-week mark. When the comparison point was the low pressure measured the day after surgery, nearly half the group showed a spike of that magnitude.6PubMed. Intraocular Pressure Spikes Following iStent Inject and the Relationship to Aqueous Outflow in Open Angle Glaucoma These spikes tend to settle within about a month, but they underscore why close monitoring in the first few weeks matters.
Suprachoroidal stents have shown even more concerning pressure behavior. In one study of the CyPass device (since withdrawn from the market for a different reason), sudden pressure elevation above 30 mmHg occurred in 37 percent of eyes, with the highest recorded spike reaching 68 mmHg. Nearly half of those spikes were asymptomatic, meaning the patient felt nothing unusual while pressure climbed to dangerous levels. About 39 percent of the patients in that study eventually needed additional glaucoma surgery.7Journal of Glaucoma. Intraocular Pressure Peaks After Suprachoroidal Stent Implantation This is a strong reminder that different stent designs carry different risk profiles, and that regular postoperative check-ups are not optional.
Scarring and Long-Term Failure
Gel stents like the XEN work by creating a drainage bleb, a small fluid-filled pocket under the thin tissue covering the white of the eye. That bleb is the stent’s exit point, and your body’s wound-healing response can scar it shut over months or years. Subconjunctival fibrosis is a common cause of long-term pressure creep after gel stent surgery.8PubMed Central. Predicting bleb revision after XEN gel stent surgery in a real-world open-angle glaucoma cohort Histological examination of failed blebs has confirmed the presence of activated fibroblasts and immune cells in the tissue, with organized scar patterns found in more than half of the specimens examined.9PubMed Central. Histopathological findings of failed blebs after microinvasive bleb surgery with the XEN Gel Stent and Preserflo MicroShunt
This scarring problem is not unique to stents; it plagues traditional trabeculectomy as well. But its importance for stent patients is that the surgery may stop working over time, requiring further intervention. In one teaching-hospital series, about 21 percent of XEN-implanted eyes met failure criteria, split evenly between patients who needed a second surgery and patients whose pressure simply never dropped enough.10PubMed Central. Safety and efficacy outcomes of the Xen45 Gel Stent use for refractory glaucoma: a surgery series from surgeon trainees at a tertiary teaching hospital A broader look at reoperation across MIGS procedures found that gel microstents had the highest 90-day reoperation rate at about 10.5 percent, compared with 2 percent for iStent-type devices and 3.3 percent for goniotomy. The most common reason for reopening was rising eye pressure, followed by stent exposure through the conjunctiva.11Journal of Cataract & Refractive Surgery. Reoperation for complications within 90 days of minimally invasive glaucoma surgery
What Happens When Scarring Starts
The standard rescue for a scarring bleb is a procedure called needling, where a fine needle is used to break up the fibrotic tissue around the stent’s exit point, combined with an injection of an anti-scarring agent such as 5-fluorouracil. Surgeons typically watch for a flattening or encapsulated bleb and rising pressure despite eye drops before deciding to needle. The postoperative regimen after needling involves anti-inflammatory drops tapered over several weeks, with careful observation of how the bleb responds.12Journal of Glaucoma. Needling With 5-Fluorouracil (5-FU) After XEN Gel Stent Implantation: 6-Month Outcomes Some patients need more than one needling session, and for some, a second surgical procedure becomes necessary when needling fails to restore adequate drainage.
Infection Risks
Endophthalmitis, a severe infection inside the eye, is rare after any glaucoma procedure but carries devastating consequences when it does occur. In one series of 293 eyes that received XEN stents, five patients (about 1.7 percent) developed endophthalmitis, appearing between 3 and 14 months after surgery.13PubMed Central. Late-onset Endophthalmitis after XEN45® Implantation: A Retrospective Case Series and Literature Review All reported cases occurred more than 30 days after the procedure. A study examining eight cases found that external exposure of the stent through the conjunctiva was present in half the patients at the time the infection was diagnosed, suggesting that an eroding or exposed stent creates a portal for bacteria. The organisms identified were staphylococcus and streptococcus species, common skin and eye-surface bacteria. Visual outcomes after endophthalmitis in these cases were described as poor.14American Journal of Ophthalmology. Endophthalmitis Associated with XEN Stent Implants
The late onset of these infections is worth emphasizing. Unlike most surgical infections that appear within the first week or two, stent-related endophthalmitis can emerge months later, triggered by gradual conjunctival thinning or erosion that exposes the device. This means you need to remain vigilant about symptoms like sudden pain, redness, or vision loss even well after you’ve recovered from the surgery itself. Reporting any visible stent tip poking through the eye’s surface to your ophthalmologist promptly is critical.
Effects on Vision and the Cornea
Any surgery on the eye raises the question of whether your vision will change beyond what the glaucoma itself would cause. One study comparing XEN gel stent implantation with trabeculectomy found that visual acuity did not change significantly over two years after the stent procedure, while trabeculectomy patients experienced a small but measurable decline.15PubMed Central. Refractive Changes after Glaucoma Surgery-A Comparison between Trabeculectomy and XEN Microstent Implantation Both procedures caused a similar degree of surgically induced astigmatism at two years, roughly three-quarters of a diopter, which is a mild amount that many people would not notice.15PubMed Central. Refractive Changes after Glaucoma Surgery-A Comparison between Trabeculectomy and XEN Microstent Implantation A separate study found that any astigmatism introduced by the XEN stent was transient, appearing at one week and resolving by two weeks with no lasting change in best-corrected vision.16PLOS ONE. Effect of Ab interno XEN gel stent implantation on corneal astigmatism
Compared with trabeculectomy, gel stents appeared to produce less corneal surface distortion at one year. Traditional trabeculectomy showed a trend toward a higher proportion of eyes developing more than one diopter of astigmatism (about 73 percent) compared with the XEN group (about 27 percent), though this particular comparison did not reach statistical significance.17PubMed Central. Comparison of Keratometric Changes After Ab Interno Gel Stent Implantation, Glaucoma Drainage Devices and Trabeculectomy
A longer-term concern is the health of the cornea’s innermost cell layer, the endothelium. These cells do not regenerate, so any loss accumulates over a lifetime. A five-year follow-up found that eyes receiving a XEN stent alone showed no significant endothelial cell loss at any point during the observation period. Eyes that had the stent combined with cataract surgery did show some loss at years two and four, though the magnitude was modest.18PubMed Central. Five-year follow-up of corneal endothelial cell density after transscleral ab interno glaucoma gel stent implantation The researchers attributed the combined-surgery loss primarily to the cataract procedure itself rather than to the stent.
How Stents Compare with Traditional Surgery
The Gold-Standard Pathway Study directly compared XEN45 gel stent outcomes with trabeculectomy in open-angle glaucoma. Postoperative complication rates were lower in the stent group: about 75 percent experienced at least one complication after the gel stent, versus about 93 percent after trabeculectomy. Hypotony rates were also roughly halved, at about 15 percent for the stent group versus 29 percent for trabeculectomy. Postoperative interventions were needed in about 40 percent of stent patients compared with 76 percent after trabeculectomy.19PubMed Central. Effectiveness and safety of the XEN45 gel stent compared to trabeculectomy in primary open-angle glaucoma: the Gold-Standard Pathway Study These numbers make clear that while the stent approach is gentler, three-quarters of patients still had some complication, usually mild. “Minimally invasive” describes the surgical technique, not the absence of side effects.
A comparative study of iStent combined with cataract surgery and endocyclophotocoagulation versus the PreserFlo MicroShunt versus XEN45 found that postoperative complications across all three groups were transient and manageable with office-based treatment.20PubMed Central. A comparison of iStent combined with phacoemulsification and endocyclophotocoagulation (ICE2) with the PreserFlo MicroShunt and XEN-45 implants That finding is reassuring, but “transient” still means days or weeks of blurred vision, discomfort, or extra clinic visits that patients should plan for.
Quality of Life After the Procedure
Despite the list of possible complications, patients who get through the early recovery period tend to report improved day-to-day functioning. A study using a validated glaucoma quality-of-life questionnaire found overall improvement in scores at six weeks after XEN45 implantation, with no individual item showing a decline.21PubMed Central. Xen45 Gel Stent implant: patient reported outcomes Part of this improvement likely reflects a reduced burden of daily eye drops, which carry their own side effects and quality-of-life costs. That said, six weeks is early, and the long-term quality-of-life picture depends on whether the stent keeps working or whether scarring forces a return to drops or additional procedures.
Special Concerns in Children
Glaucoma stent data overwhelmingly come from adults, and the pediatric picture looks different in important ways. Children have more elastic scleral tissue, which changes how the stent interacts with the eye in the first days after surgery. Surgeons have described an early pattern where pressure drops very low with a large bleb forming immediately, followed by a pressure rebound in the first week as the tissue adjusts and the drainage pathway matures. This sequence may require temporary medication and careful monitoring, which can be challenging when examining young children in a clinic setting.22Journal of Glaucoma. XEN Gel Stent in Pediatric Glaucoma
The healing response in children can also be more aggressive. A case report documented conjunctival dehiscence and tissue contraction within a month of XEN placement in a child with congenital glaucoma, a wound-healing complication that highlighted how the pediatric tissue environment differs from an adult’s.23PubMed. Multiple XEN Gel Stents for Refractory Pediatric Glaucoma Pediatric use of these devices remains off-label and based on limited case experience rather than large trials.
How Different Stent Types Distribute Risk
Not all glaucoma stents are created equal, and the specific risks shift depending on the device’s design and where in the eye it drains fluid. The broadest distinction is between trabecular bypass stents (like the iStent family), which reroute fluid through the eye’s natural drainage tissue, and subconjunctival stents (like the XEN gel stent and PreserFlo MicroShunt), which create an entirely new drainage pathway to a bleb under the conjunctiva. Trabecular bypass devices tend to produce smaller pressure reductions but avoid bleb-related complications like scarring, needling, and late infection. Subconjunctival devices achieve larger pressure drops but inherit the full suite of bleb complications familiar from traditional trabeculectomy.
Modeling studies have shown that trabecular bypass stents increase fluid flow not just at the stent location but also to nearby collector channels, extending about 1.5 clock hours past each end of the device.24PubMed Central. Modeling the Effects of Glaucoma Surgery on Intraocular Pressure This localized effect explains why these devices tend to offer more modest pressure lowering than subconjunctival stents, which bypass the natural drainage system entirely. It also explains why trabecular stents are most commonly paired with cataract surgery in milder glaucoma, while gel stents and microshunts are offered for more advanced disease where bigger drops in pressure are needed.
The 90-day reoperation data reflect this divide: gel microstents had a reoperation rate of about 10.5 percent, compared to 2 percent for trabecular bypass devices.11Journal of Cataract & Refractive Surgery. Reoperation for complications within 90 days of minimally invasive glaucoma surgery More aggressive drainage comes with a proportionally busier postoperative course. Your surgeon’s recommendation between these approaches should balance how much pressure lowering you actually need against the complication profile you’re willing to accept.
The Cost Side of Complications
Complications are not just medical events; they add cost. Every needling session, every extra office visit for a pressure spike, every additional surgery eats into whatever economic advantage a stent had over long-term medication or traditional surgery. A cost-effectiveness analysis comparing trabecular bypass stents combined with cataract surgery against medication alone found that stent-plus-cataract strategies cost less and produced slightly more quality-adjusted life-years over 35 years than either cataract surgery alone or initial nonsurgical management.25Ophthalmology Glaucoma. Cost-Effectiveness Analysis of Minimally Invasive Trabecular Meshwork Stents with Phacoemulsification But those models rely on average complication rates. If you end up in the tail of the complication distribution, needing reoperations or extended courses of anti-inflammatory treatment, the personal financial and time costs climb steeply. Insurance coverage for needling and bleb revisions varies, and the indirect cost of missed work and extra travel to the ophthalmologist’s office is rarely captured in published analyses.