The PreserFlo MicroShunt (Santen Pharmaceutical) is a glaucoma filtration device implanted via an ab externo approach1). It drains aqueous humor from the anterior chamber to the subconjunctival and sub-Tenon space, forming a filtering bleb to lower intraocular pressure.
It is classified as a bleb-forming device without a plate, and in the same category are the XEN 45/XEN 63 (AbbVie)1). It is distinguished from conventional plate-based tube shunts (Baerveldt, Ahmed) and MIGS (trabecular bypass devices)1).
| Item | PreserFlo | XEN 45 |
|---|---|---|
| Material | SIBS (silicone-based) | Porcine gelatin |
| Approach | Ab externo | Ab interno |
| Inner diameter | 70 μm | 45 μm |
Theoretically, the standardized outflow resistance based on Poiseuille’s law makes postoperative intraocular pressure more predictable compared to trabeculectomy1). Postoperative follow-up may also be simpler than conventional filtration surgery1).
Indications include primary open-angle glaucoma (POAG), pseudoexfoliation glaucoma, pigmentary glaucoma, and other glaucomas with open angles. It is considered for moderate to advanced glaucoma where MIGS is expected to provide insufficient intraocular pressure reduction1).
Contraindications are similar to other bleb-forming surgeries; poor conjunctival condition, history of conjunctival surgery, high myopia, congenital glaucoma, and secondary glaucoma are relative contraindications1).
The material and approach differ. PreserFlo is made of SIBS (synthetic polymer) and implanted ab externo (from outside the eye)1). XEN 45 is made of porcine gelatin and implanted ab interno (from inside the eye), although an ab externo approach has also been reported1). PreserFlo has an inner diameter of 70 μm, while XEN 45 has 45 μm. Both are plate-free bleb-forming devices that lower intraocular pressure by forming a filtering bleb.
Material and Dimensions
Material: SIBS (polystyrene-block-isobutylene-block-styrene). It is bioinert and also used in coronary stents. It is expected to reduce the risk of postoperative episcleral scarring and fibrosis.
Total length: 8.5 mm1)
Outer diameter: 350 μm, Inner diameter: 70 μm1)
Fin: A 1 mm fin (wing-like projection) divides the device into a distal part (3 mm) and a proximal part (4.5 mm). The fin serves to anchor the device within the scleral tunnel.
Design Principle
Hagen-Poiseuille equation: The outflow resistance of the tube is determined by its inner diameter and length. The device is designed to maintain postoperative intraocular pressure at 5 mmHg or higher as long as aqueous humor production exceeds 2 μL/min.
Bleb formation: The distal end is located approximately 6 mm posterior to the corneal limbus, allowing posterior aqueous outflow and bleb formation in the subconjunctival and sub-Tenon spaces.
Predictability: Standardized outflow resistance is thought to make postoperative intraocular pressure more predictable compared to trabeculectomy1).
The surgery is performed using an ab externo approach1). The main steps are as follows.
Mitomycin C concentration significantly affects surgical outcomes. It has been reported that 0.4 mg/mL achieves a higher medication-free survival rate than 0.2 mg/mL. However, higher concentrations of mitomycin C carry risks of bleb leakage and hypotony1).
In cases where hypotony is clinically concerning, such as in highly myopic eyes, temporary intraluminal stent placement may be considered1).
| Study | Number of Eyes | Duration | IOP Reduction |
|---|---|---|---|
| Batlle | 23 eyes | 3 years | 23.8→10.7 mmHg |
| Schlenker | 164 eyes | 1 year | Complete success 76.9% |
| Beckers | 81 eyes | 2 years | 21.7→14.1 mmHg |
In Batlle et al.’s 3-year results, intraocular pressure decreased by 55%, and the number of eye drops decreased from 2.4 to 0.7. The conditional success rate was 95%.
In a study of 164 eyes by Schlenker et al., the complete success rate at 1 year was 76.9%, and the conditional success rate was 92.5%. Low concentration of mitomycin C (0.2 mg/mL) and secondary open-angle glaucoma were independent risk factors for surgical failure.
In a prospective multicenter study by Beckers et al., the overall success rate at 2 years was 74.1%. The group using mitomycin C 0.4 mg/mL had a higher medication-free maintenance rate than the 0.2 mg/mL group (90.3% vs 51.9%).
In a randomized multicenter trial by Baker et al. (395 eyes vs 132 eyes), the surgical success rate at 1 year was higher in the trabeculectomy group (72.7% vs 53.9%). On the other hand, the incidence of transient hypotony was higher in the trabeculectomy group (49.6% vs 28.9%). Intraocular pressure was slightly lower in the trabeculectomy group (11.1 vs 14.3 mmHg).
Main Complications
Transient hypotony: The most common complication. Reported in 28.9% (Baker RCT). Most cases resolve spontaneously.
Shallow anterior chamber: Occurs with hypotony. Contact between the iris and the tube can cause tube obstruction 3)
Choroidal detachment: Reported as a complication associated with hypotony.
Tube obstruction: Occurs due to iris incarceration or IOL capture 3). Resolved with YAG laser or surgical intervention.
Case Reports from Japan
Iwasaki et al. (PMC10772340): After PMS implantation for CACG secondary to plateau iris syndrome, tube obstruction due to IOL capture occurred on postoperative day 8 3)
Course: Transient hypotony (6 mmHg) and shallow anterior chamber appeared on postoperative day 2. On postoperative day 8, intraocular pressure rose to 42 mmHg, and obstruction of the tube tip by the iris and IOL was confirmed 3)
Treatment: Using an anterior chamber maintainer, the IOL was repositioned with a Sinskey hook and the iris was removed. Postoperative intraocular pressure improved to 14 mmHg 3)
In the RCT by Baker et al., the surgical success rate at 1 year was higher in the trabeculectomy group (72.7% vs 53.9%). However, the incidence of transient hypotony was lower in the PreserFlo group (28.9% vs 49.6%), suggesting that postoperative management may be simpler 1). Recent studies have shown that PreserFlo is equivalent to trabeculectomy in medium-term intraocular pressure reduction. Device selection requires individualized judgment based on each case.
Tube obstruction occurs due to iris incarceration, blood clot, vitreous, etc. 3). YAG laser for obstruction release is often the first choice. In cases with IOL capture, surgical intervention using a Sinskey hook to reposition the IOL and open the tube lumen is performed 3). Using atropine eye drops during early postoperative hypotony may prevent tube obstruction due to iris-tube contact 3).
PreserFlo microshunt was approved in Japan in February 2022 and clinical use has begun 3). Accumulation of experience in Japan is expected in the future.
Efficacy in refractory pediatric glaucoma has also been reported; Brandt reported a 75% success rate in 12 eyes with more than 1 year of follow-up. There is potential for expanded indications in children.
A device insertion method via the ciliary sulcus has also been reported, attracting attention as an alternative approach for cases at high risk of corneal endothelial damage.
Future challenges include the following:
Postoperative management of filtration surgery is an important factor affecting surgical outcomes, and establishing a standardized postoperative management protocol is also a challenge 2).
- European Glaucoma Society. Terminology and Guidelines for Glaucoma, 6th Edition. Br J Ophthalmol. 2025.
- 日本緑内障学会. 緑内障診療ガイドライン（第5版）. 日眼会誌. 2022;126:85-177.
- Iwasaki K, Arimura S, Inatani M. Tube obstruction caused by intraocular lens capture following PreserFlo MicroShunt implantation. Am J Ophthalmol Case Reports. 2024;33:101951.
