Will bleb forming devices replace trabeculectomy in surgical treatment of primary open angle glaucoma?

Introduction Bleb forming devices (BFD) [Xen Gel Stent (Allergan INC, Dublin, Ireland) and the Preserflo MicroShunt (Santen, Osaka, Japan)] constitute an emerging subset in the concept of less invasive glaucoma surgeries. They are thin tube stents which drain into the subconjunctival space and rely on the formation of a filtering bleb to achieve their effect. They are supposed to be an alternative to trabeculectomy, and this review aims to examine the validity of this idea.Areas covered Both Xen and Preseflo are effective and safe in lowering intraocular pressure (IOP) and the number of IOP-lowering medications. This effect was sustained in the long-term (5-year) follow-up. In comparison to trabeculectomy, BFD are less effective in reducing IOP but are associated with less hypotony-related events and possibly less postoperative follow-up manipulations. BFD offer a faster visual rehabilitation compared to trabeculectomy. Current evidence does not suggest the superiority of one BFD over the other.Expert opinion Trabeculectomy continues to demonstrate higher IOP-lowering efficacy compared to BFD and remains the gold standard if lower target IOP is considered. In cases where a moderate decrease of IOP is acceptable, BFD offer significant advantages compared to trabeculectomy such as less hypotony and faster visual rehabilitation.