How Does the PreserFlo MicroShunt Stack Up Against Trabeculectomy and Other Drainage Devices?

Introduction

For people with open-angle glaucoma, surgical options aim to lower intraocular pressure (IOP) by creating a new drainage pathway for eye fluid (aqueous humor). The traditional gold-standard surgery is trabeculectomy, a technique that creates a small hole under a scleral flap, forming a filtering bleb under the conjunctiva. In recent years, newer implants have emerged. These include tube shunts (Ahmed, Baerveldt, Molteno implants) that channel fluid from the front of the eye to a plate under the conjunctiva, and minimally-invasive glaucoma surgeries (MIGS) such as the XEN Gel Stent and PreserFlo MicroShunt.

The PreserFlo MicroShunt (formerly InnFocus MicroShunt) is a small, ab-externally implanted glaucoma device made of a soft polymer (poly(styrene-block-isobutylene-block-styrene), or SIBS). It drains fluid from the anterior chamber into a posterior subconjunctival bleb. This device is meant to be less invasive than trabeculectomy yet more effective than purely bleb-less MIGS. In this review, we compare PreserFlo to trabeculectomy and other drainage devices (Ahmed valve, Baerveldt and Molteno implants, XEN stent) in terms of how they work, clinical effectiveness, safety, practical use, and current access/cost issues.

We use evidence from published trials and registries. When we report results, we note sample sizes and study years. If data are limited or mixed, we say so. Key findings are summarized in the concluding table.

Background and Mechanism

PreserFlo MicroShunt: The PreserFlo device is an 8.5 mm long tube with a 350 µm outer diameter and a very narrow 70 µm inner lumen (pmc.ncbi.nlm.nih.gov). It is made of SIBS, a biocompatible polymer that resists biodegradation (pmc.ncbi.nlm.nih.gov). The surgeon opens a small conjunctival/Tenon’s flap (much like for trabeculectomy) and uses mitomycin-C (an antifibrotic) under the flap. The MicroShunt is inserted ab externo: a tiny pocket is made in the sclera to accept the device fins, and a tunnel is made into the anterior chamber. The proximal tip sits inside the eye (just anterior to the iris) and the distal end drains fluid beneath the conjunctiva (see image below). Because the lumen is very small, it provides some flow resistance to help prevent severe postoperative hypotony (very low pressure).

(pmc.ncbi.nlm.nih.gov)
Figure: The PreserFlo MicroShunt (red arrow) shunts aqueous humor from the anterior chamber (right) to a bleb under the conjunctiva (left) (pmc.ncbi.nlm.nih.gov).

Trabeculectomy: In trabeculectomy, the surgeon creates a scleral flap and manually makes an opening under it (sometimes removing a small piece of iris) to connect the anterior chamber to the subconjunctival space. This creates a bleb. Mitomycin-C is often applied. Trabeculectomy is highly effective at lowering IOP, but it is invasive: it requires extensive dissection, sutures, and careful postoperative management.

Tube Shunts (Ahmed, Baerveldt, Molteno): These are aqueous drainage implants. A silicone tube is inserted through the sclera into the anterior chamber. The tube drains fluid to a plate placed under the conjunctiva. The Ahmed Glaucoma Valve (AGV) includes a one-way valve designed to prevent early hypotony. The Baerveldt implant (typically 350 mm² plate) and Molteno implant (typically 275–350 mm²) are non-valved; surgeons ligate or occlude the tube temporarily to prevent immediate overdrainage. In general, valved shunts (Ahmed) cause less early hypotony but may end up at slightly higher pressures, while large non-valved shunts (Baerveldt, Molteno) can achieve lower long-term IOP but risk early overdrainage if not carefully tied off.

XEN Gel Stent: The XEN 45 is a soft, gelatin-based 6 mm tube with a 45 µm lumen. It is implanted ab interno (from inside the eye) through a small corneal incision. It also drains to a subconjunctival bleb. No scleral dissection or removable flap is needed – only a gentle subconjunctival elevation of conjunctiva is done and mitomycin-C is often injected under the conjunctiva. Because the XEN lumen is slightly larger than the aqueous outflow resistance of normal trabecular pathways, it provides a controlled flow (and 45 µm lumen is internally limiting flow to avoid hypotony). However, like PreserFlo, it relies on bleb formation and often requires postoperative management (needling) of the bleb.

MIGS vs Traditional Spectrum: Surgical options range from classic filtration surgery (trabeculectomy/tubes) at one end to ab interno MIGS at the other. MIGS are generally defined as procedures with an ab interno approach, minimal tissue trauma, faster recovery, and a good safety profile (pmc.ncbi.nlm.nih.gov). Examples of ab interno MIGS that do not form a bleb include stents in Schlemm’s canal (iStent, Hydrus) or suprachoroidal devices. PreserFlo, XEN, and older shunts are unique because they do create a bleb. These “bleb-forming MIGS” are sometimes considered intermediate: they are less invasive than trabeculectomy (especially XEN, which is minimally dissected) but not as simple as trabecular bypass stents. In practice, PreserFlo and XEN are often lumped into the MIGS group (despite ab externo steps in PreserFlo’s case) because they aim to reduce invasiveness and management burden.

Efficacy Outcomes

IOP Reduction and Success Rates: Clinical studies show that PreserFlo consistently reduces IOP into the mid-teens. In Baker et al. (2021), a large randomized trial of 527 eyes (395 PreserFlo, 132 trab) reported one-year IOP falls from 21.1±4.9 to 14.3±4.3 mmHg (–29% from baseline) after MicroShunt, versus 21.1±5.0 to 11.1±4.3 mmHg (–45%) after trabeculectomy (www.sciencedirect.com). Corresponding mean glaucoma medications dropped from 3.1 to 0.6 in the PreserFlo group and 3.0 to 0.3 in the trab group (www.sciencedirect.com). By Baker’s success criteria (≥20% IOP reduction without more meds), 53.9% of PreserFlo eyes and 72.7% of trabeculectomy eyes “succeeded” at 1 year (P<0.01) (www.sciencedirect.com). This shows that trabeculectomy gave a somewhat larger pressure drop and higher success per this definition.

A single-center prospective study by Fili et al. (2022) also compared PreserFlo (150 eyes) vs trabeculectomy (150 eyes) in moderate-to-advanced glaucoma. At 12 months, 81.3% of MicroShunt eyes and 94.0% of trabeculectomy eyes achieved >20% IOP reduction without medications (pmc.ncbi.nlm.nih.gov). Mean IOP at 1 year was 12.9±3.4 mmHg (PreserFlo) and 11.4±4.5 mmHg (trab) (pmc.ncbi.nlm.nih.gov). Medications fell from ~2.5 to 0.4 in the PreserFlo group and to 0 in the trab group (pmc.ncbi.nlm.nih.gov). These results again favor trabeculectomy for lower final IOP, though both groups reached low teens pressures.

Other PreserFlo series report similar IOP control. For example, Beckers et al. (2022) studied 81 eyes with PreserFlo at 2 years. Mean IOP fell from 21.7±3.4 mmHg at baseline to 14.5±4.6 mmHg at 1 year and 14.1±3.2 mmHg at 2 years (P<0.0001) (pubmed.ncbi.nlm.nih.gov). Overall success (with or without meds) was 74.1% at 1 year (pubmed.ncbi.nlm.nih.gov). Medications dropped from 2.1 to 0.5 (mean) by 2 years, with 73.8% of patients medication-free (pubmed.ncbi.nlm.nih.gov). In their study, higher mitomycin-C (0.4 mg/ml) trended toward better pressure and med reduction than 0.2 mg/ml (pubmed.ncbi.nlm.nih.gov).

PreserFlo vs XEN: Available data suggest similar efficacy between these two bleb-based MIGS. In a 2-year comparative series, Scheres et al. (2022) found that mean IOP dropped from 20.1 to 12.1 mmHg (PreserFlo) and from 19.2 to 13.8 mmHg (XEN) at 2 years (p=0.19) (research.tue.nl). The probability of “qualified success” (achieving target IOP with or without meds) was 79% for PreserFlo vs 73% for XEN at 24 months (research.tue.nl). Both groups had substantial medication reduction. Thus, in this series the two devices gave nearly equivalent pressure outcomes.

PreserFlo vs Tube Shunts (Ahmed/Baerveldt): There are no head-to-head trials of PreserFlo versus tube implants. For context, device trials provide a ballpark: The Ahmed vs Baerveldt ABC Study showed at 1 year mean IOP ~15.4 mmHg with Ahmed vs 13.2 mmHg with Baerveldt when starting from 31 mmHg (www.aaojournal.org). Both used adjunctive medications. These results imply that large plate tube shunts can achieve very low pressures (down to ~13 mmHg) often slightly lower than PreserFlo’s typical outcome (low teens). On the other hand, tubes carry more serious surgery for difficult cases. In practice, PreserFlo tends to be used in mild-to-moderate glaucoma; Ahmed/Baerveldt in refractory or severe cases.

Longer-Term Durability: Prestigious controlled data (like Baker et al.) reported only 1-year results so far. Longer follow-up is still needed. In the Beckers 2-year series, PreserFlo pressure control was sustained at ~14 mmHg through 2 years (pubmed.ncbi.nlm.nih.gov). Fili’s study was only 1 year. The Scheres XEN vs PreserFlo study also had 2-year data (research.tue.nl). Notably, Baker’s trial is designed for 2 years (NCT01881425), and longer-term data should clarify durability of the MicroShunt vs trabecular outcomes.

Safety and Complications

Hypotony (Low IOP): Shunt surgeries often have early postoperative hypotony. In Baker et al., transient IOP ≤5 mmHg occurred in 28.9% of PreserFlo eyes versus 49.6% of trabeculectomy eyes (P<0.01) (pmc.ncbi.nlm.nih.gov). Thus, while PreserFlo had less frequent shallow pressure than trab, more than a quarter of eyes did have an IOP hump to ≤5 mmHg after MicroShunt. Serious hypotony-related complications (maculopathy or required reformation) were uncommon in both arms (www.sciencedirect.com). In other series, rates of transient hypotony after PreserFlo range up to ~30–40% (usually mild and resolving) (pmc.ncbi.nlm.nih.gov). In contrast, classic trabeculectomy studies report chronic hypotony (IOP <5 mmHg) in a significant minority at 3–5 years (23–31% in Tube vs Trabeculectomy study) (pmc.ncbi.nlm.nih.gov). Ahmed valves (valved shunts) generally have lower hypotony rates than non-valved tubes, but can still have periods of low IOP in the early hypertensive phase.

Choroidal Effusion/Detachment: Fluid can collect under the retina when pressures are low. PreserFlo series report choroidal detachment in a few percent to over 10% of eyes (pmc.ncbi.nlm.nih.gov). Baker’s trial showed choroidal detachments occurred more with trab (data not explicitly given but implied by higher hypotony), and PreserFlo had 6.1% vs 13.7% hypotony (not choroid) (pmc.ncbi.nlm.nih.gov). By contrast, Ahmed and Baerveldt implants often have low IOP but choroid changes are usually less dramatic (the encapsulated bleb tends to stabilize pressure before major effusion).

Bleb-Related Issues (Leak, Infection): Any surgery that makes a conjunctival bleb risks leaks or infection. In Baker et al., no Seidel-positive bleb leaks were seen in the PreserFlo group, whereas 6 cases occurred after trabeculectomy (p=0.024) (pmc.ncbi.nlm.nih.gov). In general, PreserFlo’s more posterior bleb and small tube may reduce leak risk. Late bleb infections (blebitis or endophthalmitis) are rare but serious. In the published literature, endophthalmitis has been reported after XEN in up to ~3% of eyes; by contrast, only a few cases of PreserFlo exposure (and no confirmed infections) have been reported (pmc.ncbi.nlm.nih.gov). Ahmed/Baerveldt shunts also have risk of conjunctival erosion over the plate or tube (reports range ~2–7% exposure) (www.dovepress.com), which can lead to endophthalmitis if not managed. Trabeculectomy blebs can likewise become infected (up to ~5–7% blebitis in long term). Overall, PF and XEN share the same spectrum of bleb-related risks as trabeculectomy, while tubes carry plate erosion risk specific to their design.

Hyphema (Bleeding in Eye): Mild blood reflux often occurs after any glaucoma surgery. In Baker’s RCT, frank hyphema was noted in 6.1% of PreserFlo eyes vs 2.3% of trab (difference not statistically significant) (pmc.ncbi.nlm.nih.gov). Most small hyphemas self-resolve without issue. Tube shunts can also cause hyphema, especially if placed in an anterior chamber with rubbing iris or neovascular membranes. XEN and other MIGS typically have low rates of significant hyphema.

Need for Re-Operations or Interventions: Postoperative interventions (suture lysis, bleb needling, etc.) were common. Baker found 40.8% of MicroShunt eyes required laser suture lysis or similar procedures, vs 67.4% of trabeculectomy eyes (www.sciencedirect.com). Similarly, Fili et al. observed fewer re-operations in the PreserFlo group. Needling of the bleb (to revive scarring) occurred in roughly 5–19% of PreserFlo cases in published series (pmc.ncbi.nlm.nih.gov), compared to much higher rates with XEN (22–43%) . Ahmed/Baerveldt implants sometimes require bleb revision or valve adjustment, especially if the encapsulated plate under-drains; roughly 15–50% of tube eyes may need eye drops or surgical revision over time. Overall, PreserFlo tends to need fewer needle bleb revisions than ab interno stents, and modestly lower rates of suture/loss procedures than trabeculectomy.

Corneal Endothelial Cell Loss: Devices placed in the anterior chamber can rub on or injure the cornea over time. The PreserFlo’s tube lies parallel to the iris, usually away from cornea. No large studies have reported marked endothelial cell loss (ECD) with PF to date. By contrast, Ahmed and Baerveldt tubes in the AC can cause progressive ECD loss. For example, one study found a 9.4% drop in central ECD at one year after Ahmed valves, versus only ~3% loss after trabeculectomy (pmc.ncbi.nlm.nih.gov). Another report showed no significant difference in 2-year ECD loss between Ahmed and Molteno implants (both ~12%) (pmc.ncbi.nlm.nih.gov). In short, bleb-forming MIGS like PreserFlo/XEN likely have minimal direct endothelial impact, while tube shunts in the AC can accelerate corneal cell loss (particularly if the tube is too close to the endothelium).

Surgical and Practical Considerations

Technique and Operative Time: Traditional trabeculectomy requires conjunctival peritomy, large scleral flap dissection, iridectomy, suturing, and MMC exposure. It is technically demanding with a steep learning curve. PreserFlo implantation is ab externo but involves a smaller dissection: the surgeon only needs ~90–120° of conjunctival/Tenon’s flap, a deep scleral pocket (1 mm × 3 mm) to hold the device fins, and a needle track into the anterior chamber (pmc.ncbi.nlm.nih.gov) (pmc.ncbi.nlm.nih.gov). No iridectomy is needed. After placing the MicroShunt in the pocket, the flap is closed watertight. The procedure is generally faster and simpler than trabeculectomy, though it still requires careful MMC use (typically 0.2–0.4 mg/mL for 2–3 minutes) (pmc.ncbi.nlm.nih.gov). Surgeons report a moderate learning curve: easier than mastering trabeculectomy, but needing precision.

In comparison, the XEN stent is even less invasive: it is inserted via a small corneal incision (ab interno) with minimal conjunctival handling, making it very quick and preserving tissue. Tube shunts (Ahmed, Baerveldt, Molteno) require more extensive dissection similar to a trabeculectomy, plus placement of the large plate under Tenon’s, so operative time is usually longer than for PreserFlo. In short, PreserFlo lies between very-minimal MIGS (like XEN) and full trabeculectomy or tube surgery.

Use of Antifibrotics: All bleb-forming surgeries use antiscarring drugs. Trabeculectomy often uses MMC (e.g. 0.1–0.5 mg/mL). In PreserFlo implantation, MMC is routinely applied (often 0.2 or 0.4 mg/mL for 2–3 min) to boost success (pmc.ncbi.nlm.nih.gov). The faucet is fully open – without it, failure rates are high. XEN and tubes also use antimetabolites (MMC or 5-FU). One practical note: higher MMC (0.4 vs 0.2 mg/mL) in PreserFlo has been linked to more medication-free eyes (pubmed.ncbi.nlm.nih.gov), but also potentially more initial IOP dips. Surgeons balance potency and safety case-by-case.

Postoperative Management: After trabeculectomy, frequent clinic visits and suture adjustments are typical. PreserFlo patients also need close follow-up in the early months, but perhaps slightly fewer interventions. Needling of the bleb is done in a minority (5–15%) of PreserFlo cases if the pressure creeps up (pmc.ncbi.nlm.nih.gov). Overall, studies show that PreserFlo patients undergo significantly fewer postoperative manipulations than trabeculectomy patients (www.sciencedirect.com). Nonetheless, the postoperative course is not trivial: a counting plate needs monitoring for flat chambers or leaks, and steroid taper can take a while (often longer than non-bleb MIGS).

Patient Selection: Ideal candidates for PreserFlo are patients with primary open-angle glaucoma who require more IOP lowering than medication can provide, but who still have some healthy conjunctiva. It has been used in primary open-angle and pseudoexfoliation glaucoma. It tends to be offered for moderate glaucoma (for which MIGS like iStent might not suffice, but full trabeculectomy might be deferred) (pmc.ncbi.nlm.nih.gov) (pubmed.ncbi.nlm.nih.gov). Eyes with previous conjunctival scarring (failed trab, chronic inflammation, symblepharon) are less ideal for any bleb surgery. Also, very advanced or low-target glaucoma may still favor traditional trab or tube because PreserFlo often does not reach the single-digit IOP that such eyes sometimes need (www.sciencedirect.com) (pmc.ncbi.nlm.nih.gov).

By contrast, trabeculectomy is classically reserved for those needing the absolute lowest IOP or who have failed other measures. Tube shunts (Ahmed/Baerveldt) are often chosen when trabeculectomy is likely to fail (previous surgery, uveitic/neovascular glaucoma) or in younger patients at high risk of trab failure. XEN stent is typically a choice for mild-to-moderate glaucoma, especially when combining with cataract surgery, or when less-invasive surgery is desired. In summary, PreserFlo fills a middle niche: more aggressive than Schlemm’s-canal MIGS, but somewhat gentler than trabeculectomy.

Cost, Access, and Regulatory Status

Approval Status: The PreserFlo MicroShunt has CE mark approval in Europe and is licensed in Canada and other regions, but as of late 2023 it is not yet FDA-approved in the United States (pmc.ncbi.nlm.nih.gov). It is available in the US only through clinical trials. By contrast, Ahmed valves and Baerveldt/Molteno tubes have long been FDA-approved for refractory glaucoma in the US. The XEN 45 Stent was FDA-approved in 2016 for use in open-angle glaucoma (with or without cataract) in the US.

Reimbursement and Cost: Costs vary widely by healthcare system. An analysis from the UK (where healthcare is publicly funded) found that PreserFlo surgery saved around £245–£566 per eye compared to trabeculectomy, mainly because of fewer follow-up visits and interventions (www.sciencedirect.com). In that study, PreserFlo had a slightly higher device cost but overall lower post-op care costs. By contrast, an older U.S. Medicare-based analysis (of early trial data) estimated the PreserFlo procedure would cost about $2,058 more per patient than trabeculectomy, largely due to the expensive implant and currently low reimbursement (www.sciencedirect.com). XEN stents and tube implants also involve significant device costs, but long-term cost-effectiveness depends on surgical success and need for additional interventions. As of now, formal cost-effectiveness studies are limited, but one can say that if PreserFlo largely replaces trabeculectomy, payers will want evidence of overall savings or at least similar outcomes for the higher price of the device.

Expert Perspectives and Controversies

PreserFlo has sparked debate in the glaucoma community. Proponents argue that it offers a predictable and easier alternative to trabeculectomy for many patients: it avoids some of trabeculectomy’s nuances (iridectomy, multiple scleral sutures) and seems to have a good intermediate safety profile. Critics note that the IOP reduction achieved is generally less than trabeculectomy, and some caution that the term “minimally invasive” may overstate the ease of the surgery. In other words, PreserFlo still requires a filtering bleb and postoperative care, so it is not “just another MIGS stent.” There are concerns that cobbling onto the MIGS trend might mislead both doctors and patients about the surgery.

Some surgeons hoped PreserFlo would rival trabeculectomy’s effectiveness more closely. For example, Baker et al. showed a notable gap in mean IOP and success rate between the MicroShunt and trabeye (www.sciencedirect.com). This has led to debate: should PreserFlo be used in advanced glaucoma when such gaps matter, or is it better reserved for moderate cases? Also, because early data are mostly one-year and from industry-supported studies, experts call for caution and independent long-term data. As Rowson et al. (2022) noted for MIGS broadly, much of the current evidence is of lower quality (retrospective or observational) and often industry-funded (pmc.ncbi.nlm.nih.gov). They emphasize the need for more randomized trials and long-term follow-up.

In summary, the role of PreserFlo is still being defined. It clearly has a place between traditional trabeculectomy and the gentler MIGS. Surgeons may disagree on the exact indications. Some predict it will become a first-line surgical option for early progressive glaucoma, avoiding trab in many cases; others worry it may compromise outcomes in those who really need the pressure drop that only a trab can give. Usage patterns will likely evolve as more data emerge and as US approval status is resolved.

Comparative Summary

Conclusion

The PreserFlo MicroShunt is an intermediate glaucoma surgery: more effective at lowering IOP than many non-bleb MIGS but less invasive (and somewhat safer) than traditional trabeculectomy. In trials and series, it reliably lowers IOP into the low teens and dramatically cuts medication use (www.sciencedirect.com) (pubmed.ncbi.nlm.nih.gov). Compared to trabeculectomy, it generally causes less early hypotony and requires fewer postoperative interventions (www.sciencedirect.com) (pmc.ncbi.nlm.nih.gov), but trab often achieves a slightly lower final pressure. Compared to tube shunts, PreserFlo is simpler to implant and avoids an anterior chamber tube, though large tubes may achieve even lower pressures in refractory cases (www.aaojournal.org). Compared to the XEN stent, PreserFlo appears similarly effective in IOP control, though perhaps slightly less needling is needed with the MicroShunt (research.tue.nl) .

Safety-wise, PreserFlo shares the bleb-related risks of trab and XEN (bleb leak, infection, detachment), but in practice these complications have been infrequent to date. Notably, no significant transplanted vision-threatening events have emerged in studies, and chronic hypotony is uncommon (pmc.ncbi.nlm.nih.gov) (pmc.ncbi.nlm.nih.gov). Importantly, because it avoids an AC tube, PreserFlo likely spares the corneal endothelium that can be damaged by Ahmed/Baerveldt tubes (pmc.ncbi.nlm.nih.gov).

Surgeons consider PreserFlo for eyes needing more pressure lowering than simple MIGS can give, but who might not yet need full trabeculectomy. It requires good conjunctiva and patient willingness for bleb follow-up. Costs and approval are still hurdles in some regions (e.g. awaiting FDA approval in the US). In conclusion, based on current evidence PreserFlo lives up to its billing as a “minimally invasive” bleb surgery: it offers an attractive balance of efficacy and safety, but it is not a drop-in replacement for trabeculectomy, nor a mere variant of tube shunts. Its precise place will continue to be refined by ongoing studies and surgeon experience.

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