The Xen-45 gelatin microstent (Allergan, Dublin, Ireland) is a novel, bleb-forming microinvasive glaucoma surgery (MIGS). Creation of a filtering bleb through the gel stent and under the conjunctiva lowers intraocular pressure (IOP) by bypassing the natural outflow pathway of aqueous. A recent retrospective cohort study showed comparable safety and risk of failure to trabeculectomy. Amongst the main advantages of this device is the ability to create a bleb without dissecting and disrupting tissue, thus decreasing the amount of wound healing and potentially limiting bleb failure. However, despite demonstrating similar efficacy and safety to trabeculectomy,2 the Xen-45 gelatin microstent continues to suffer from occasional surgical failure due to fibrosis of the filtering bleb, and obstruction of the stent. Although antimetabolites, such as mitomycin C, have decreased reactionary wound healing that can result following surgery, fibrosis may still occur, especially when the components of the Xen-45 gelatin microstent are in close proximity to the fibroblastic structures of tenon's fascia.Tenon's capsule resembles a sponge-like layer with multiple adhesions to the overlying conjunctiva and underlying episclera. Implantation of the XEN within this space creates a higher risk of obstruction and subsequent failure. To ensure the lowest potential for occlusion, bleb scarring, and failure, one must ensure careful placement of the device in the subconjunctival space, avoiding intra-tenon's placement. Placement in the supra-tenon's space is believed to maximize aqueous outflow, while preventing obstruction, limiting fibrosis of the bleb, and promoting long-term patency. Despite the theoretical merits, long-term data of outcomes after targeted supra-tenon's placement is needed to fully assess its potential in improving Xen-45 microstent outcomes.
