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

This audio article is from VisualFieldTest.com.Read the full article here: https://visualfieldtest.com/en/how-does-the-preserflo-microshunt-stack-up-against-trabeculectomy-and-other-drainage-devicesTest your visual field online: https://visualfieldtest.comSupport the show so new episodes keep coming: https://www.buzzsprout.com/2563091/supportExcerpt: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 (). It is made of SIBS, a biocompatible polymer that resists biodegradation (). 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). () Figure: The PreserFlo MicroShunt (red arrow) shunts aqueous humor from the anterior chamber (right) to a bleb under the conjunctiva (left) (). 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 (). 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 (). 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 (). 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) (). 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 (). Mean IOP at 1 year was 12.9±3.4 mmHg (PreserFlo) and 11.4±4.5 mmHg (trab) (). Medications fell from ~2.5 to 0.4 in the PreserFlo group and to 0 in the trab group (). 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) (). Overall success (with or without meds) was 74.1% at 1 year (). Medications dropped from 2.1 to 0.5 (mean) by 2 years, with 73.8% of patients medication-free (). In their study, higher mitomycin-C (0.4 mg/ml) trended toward better pressure and med reduction than 0.2 mg/ml (). 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) (). The probability of “qualified success” (achieving target IOP with or without meds) was 79% for PreserFlo vs 73% for XEN at 24 months (). 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 (). 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 (). Fili’s study was only 1 year. The Scheres XEN vs PreserFlo study also had 2-year data (). 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) (). 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) weSupport the show