A second group of procedures places a device into the meshwork to attempt to improve outflow (iStent, Hydrus). These stents made of metal inserted into the trabecular meshwork with the concept that the opening in the stent will provide an outflow channel to lower eye pressure better. The FDA has only approved these surgeries for patients who are also undergoing cataract surgery at the same time, and in each case the initial results suggested that the stent gave significantly lower eye pressure than cataract surgery alone, though more of the effect was due to the cataract surgery. The pressure lowering effect of Hydrus has been shown to last for 5 years and its effect was better than versions of the iStent in a randomized trial comparing the two. Inserting stents adds a few minutes to cataract surgery. All materials in eye surgery devices are safe for an MRI scanner and you would not set off the TSA metal detector. There have been no reported problems with this group of devices eroding out of the eye, falling out of place, or causing damage to the eye otherwise, so their safety level is very good. Such was not the case for a device called CyPass, which was also an artificial tube-like device placed at cataract surgery, but into the space between the two layers called choroid and sclera with its open end in the front chamber of the eye. Like the other stents, it was intended to lower eye pressure, but by letting aqueous out through the uveoscleral pathway. Approved in 2016 by the FDA, it was removed from use by the company in 2018 when the data began to suggest that damage to the cornea was occurring in eyes with CyPass, potentially leading to a need for corneal replacement in the future. This stresses the need to monitor the safety and effectiveness of new (and old) procedures for glaucoma.

A final type of newer surgery involves placement of a tube-like device into the front chamber of the eye and leading aqueous humor to exit under the conjunctiva (XEN and PreserFlo MicroShunt). They differ from the tube-shunt because they don’t have a reservoir to accept the aqueous, so they often have a bleb, like trabeculectomy. Both devices require opening the conjunctiva and making an opening into the eye, though typically no iris hole is made. In a direct, randomized comparison trial of MicroShunt to trabeculectomy, the success rate of trabeculectomy was better. The XEN device is made of porcine gelatin, so if you have religious beliefs that restrict you from having medical devices that are derived from pigs implanted in your body, you should have a conversation with your religious leader. Unlike trabeculectomy, the pressure with XEN or MicroShunt cannot be adjusted in the early postoperative period, as there are no adjustable sutures. When the pressure is not controlled adequately, reoperations called needling are done, sometimes more than once to improve the chance of success with the two procedures.