Subconjunctival Microinvasive Glaucoma Surgeries

An Update on the Xen Gel Stent and the PreserFlo Microshunt

Anna T. Do; Hardik Parikh; Joseph F. Panarelli

Disclosures

Curr Opin Ophthalmol. 2020;31(2):132-138. 

In This Article

PreserFlo MicroShunt: Technique, Outcomes, and Complications

The PreserFlo MicroShunt is an 8.5-mm tube with a 70-μm lumen that shunts fluid from the anterior chamber to the subconjunctival/sub-Tenon's space. The tube is composed of poly(styrene-block-isobutylene-block-styrene) or SIBS, an inert thermoplastic polymer. It was initially used in drug-eluting stents in coronary arteries and has been found to induce minimal tissue inflammation/encapsulation.[25] There are two fins on the tube that are 4.5 mm from the anterior tip to prevent anterior migration, peritubular leakage and maintain orientation of the bevel of the tube toward the cornea.[26]

The procedure involves dissection of a scleral pocket, application of MMC, and tube insertion through a 3-mm-long 25-G needle tract. The proximal end of the shunt extends approximately 2–3 mm into the anterior chamber. Flow is confirmed by observing drop formation at the distal end of the tube prior to closing the peritomy.

The shunt has been approved in Europe since 2012 and has not yet received FDA approval in the USA. The longest retrospective observational study to date reports three-year outcomes on 23 mixed-race patients in the Dominican Republic with primary open-angle glaucoma that received the PreserFlo MicroShunt (14 eyes with the shunt alone, 9 eyes with combined cataract surgery).[27] Follow-up results were reported at one and three years.[27–29] Glaucoma medications were discontinued immediately after surgery and were reintroduced at the surgeons' discretion if IOP was not adequately controlled. IOP reductions at one, two, and three years were 55, 50, and 55%, respectively. Baseline mean preoperative IOP of 23.8 ± 5.3 mmHg on 2.4 ± 0.9 medications decreased to a mean of 10.7 ± 3.5 mmHg on 0.7 ± 1.1 medications at three years. Sixty-four percent of patients were off all glaucoma drops at three years. Most of the complications were transient or resolved with office-based interventions. One patient failed because of bleb encapsulation and had an uncontrolled IOP at 27 months, necessitating placement of a second MicroShunt. Choroidal detachments occurred in two patients; both resolved with conservative management. Other complications included: one eye with elevated IOP requiring fibrin removal from the lumen of the tube, one eye with elevated IOP that required late-stage needling, and one eye with an early bleb leak that spontaneously resolved by two weeks.

In a multicenter study by Beckers et al.[30] in France, Dominican Republic, and the Netherlands, 91 consecutive eyes had PreserFlo MicroShunts inserted. Average IOP was lowered by 45.3% (24.3 ± 5.9 to 13.3 ± 4.0 mmHg) after one year. Ninety percent of patients had an IOP less than 18 mmHg and 83% of patients were off all glaucoma medications. Adverse events included transient hypotony [11% (IOP < 6 mmHg)], and hyphema, all of which resolved within three months without further surgical intervention. There were no vision-threatening adverse events.

A prospective randomized FDA clinical trial comparing the safety and efficacy of the PreserFlo MicroShunt to trabeculectomy in POAG is underway (NCT0188425). Another clinical trial in the Netherlands (NCT03931564) aims to compare the cost-effectiveness of the PreserFlo MicroShunt to trabeculectomy and is expected to complete by July 2022.

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