Positioning the ExPRESS shunt in the glaucoma surgeon's practice
Among the growing plethora of glaucoma surgical procedures, trabeculectomy remains the most commonly performed procedure due to its track record of achieving low target pressures. Although trabeculectomy has been performed for decades the procedure has evolved over time including the introduction of releasable sutures/suture lysis, the use of anti-metabolites and conjunctival flap design making the modern trabeculectomy very effective at lowering IOP with reduced risks. Potential serious complications exist, however, such as early and late postoperative hypotony, reduced vision due to accelerated cataract growth and bleb-associated infections.
Originally the device was intended to be implanted directly under the conjunctiva, however, due to high rates of hypotony and device extrusion it is now implanted under a scleral flap. This is essentially a modification of a trabeculectomy, with the elimination of manually creating an osteium and a peripheral iridectomy.
Given the similarity to a trabeculectomy, the procedure has a short learning curve specifically for those familiar with trabeculectomy surgery. It was also anticipated that the uniform internal lumen diameter of the shunt would yield more consistent reduction in IOP and specifically reduce rates of early hypotony. Further proposed advantages over conventional trabeculectomy include decreased tissue manipulation by excluding the manual creation of an osteium and peripheral iridectomy, which could result in improved IOP lowering over a trabeculectomy.
The procedure of implanting an ExPRESS shunt under a scleral flap has been embraced by many glaucoma surgeons with thousands of devices implanted worldwide. Unfortunately, what is missing in the literature are well-designed prospective randomized controlled trials (RCTs) comparing the device implanted under a scleral flap to a trabeculectomy. Comparative data of this nature would provide conclusive evidence to secure the position of the ExPRESS shunt in the glaucoma surgical armamentarium.