Subconjunctival Microinvasive Glaucoma Surgeries

An Update on the Xen Gel Stent and the PreserFlo Microshunt

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


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

In This Article

Abstract and Introduction


Purpose of review: This review will provide an update on surgical techniques, outcomes, and complications for two new translimbal bleb-forming surgical glaucoma devices.

Recent findings: The XEN Gel Microstent and PreserFlo MicroShunt comprise a category of subconjunctival microinvasive glaucoma surgery developed with the aim of improving the predictability and safety profile of bleb-forming procedures. Both devices are made of noninflammatory material which limits postsurgical inflammation and scarring and have a valve-less intrinsic flow-limiting design, which decreases the risk of hypotony. There are various techniques of implantation for the XEN Gel Microstent each with their own advantages and disadvantages.

Summary: These devices have demonstrated promising outcomes in early experimental literature with similar intraocular pressure-lowering effects to traditional incisional surgery such as trabeculectomy or tube shunt surgery, but with fewer risks. Future randomized, prospective studies should be done to compare these gel stents and microshunts both to each other and to other traditional glaucoma surgeries.


Glaucoma is the leading cause of irreversible blindness worldwide.[1,2] Intraocular pressure is currently the only modifiable risk factor, and lowering intraocular pressure (IOP) through medications, laser treatment, or incisional surgery are the only means by which progression of visual field loss can be prevented.[3] Although many patients can achieve adequate IOP control with topical medications and/or laser trabeculoplasty, others continue to progress despite conservative treatment and ultimately require surgical intervention. Glaucoma surgery aims to achieve one of the following: decrease aqueous humor production from the ciliary body, increase flow through the conventional outflow network by bypassing the juxtacanalicular tissue of the trabecular meshwork, increase uveoscleral outflow, or shunt aqueous humor from the anterior chamber to the subconjunctival space.[4]

The trabeculectomy was first introduced in 1968 as a filtering surgery that produced a subconjunctival bleb.[5] The subconjunctival space has a high capacity for outflow, which is why bleb-forming procedures are able to achieve lower IOPs compared with other bleb-less drainage spaces (i.e., Schlemm's canal, suprachoroidal space). Since that time, much effort has been made to improve the performance of trabeculectomy and other filtering procedures. Although the trabeculectomy is extremely effective at reducing IOP in the short term, surgical failure rates still range between 37 and 60% at five years even with the adjunctive use of mitomycin C (MMC) or 5-fluorouracil.[6] Most early complications following a trabeculectomy are transient and self-limited, but a host of serious long-term complications, including blebitis and bleb-related endophthalmitis, can occur years after the initial procedure.[7–9]

There continues to be a need for safer and equally effective alternatives for patients with moderate/advanced disease in need of a low IOP. With the advent of microinvasive glaucoma surgeries (MIGS), there has been a renaissance in the surgical management of glaucoma. MIGS procedures are minimally traumatic to the targeted tissue, offer improved safety profiles, shorter operating times, and a rapid recovery of visual acuity.[10] The MIGS devices which target the trabecular meshwork or Schlemm's canal are great options for patients with mild-to-moderate glaucoma in need of a modest IOP reduction. For patients with more advanced disease, subconjunctival filtration devices may be a more suitable surgical option as they have demonstrated better efficacy while still offering a favorable safety profile.

In this review, we discuss the surgical techniques, outcomes, and complications of two subconjunctival bleb-forming MIGS procedures, the XEN Gel Microstent (XEN-GGM, Allergan Plc, Parsippany, NJ, USA) and the PreserFlo MicroShunt (Santen, Japan).