FDA approves Hydrus microstent

Thomas W. Samuelson, MD

The recent FDA approval of Hydrus has been long anticipated. My first experience with the device, well before it was called “Hydrus,” was in the basement labs of the Phillips Eye Institute in 2007. Indeed, the innovative process from concept to commercialization is arduous and lengthy. Yet, thanks to two recent FDA approvals, glaucoma-anterior segment surgeons now have a third device option for indwelling canal trabecular micro-bypass as the Hydrus joins the first and second generation iStents (Glaukos) in this rapidly growing segment. The Hydrus is novel in several ways. First, it is comprised of nitinol, which has a long track record in human use. It has an 8-mm length, which when deployed extends nearly 3 full clock hours of the angle. This essentially eliminates the need for “intelligent placement,” in that the Hydrus spans the entire inferonasal quadrant and the rich supply of collector channels typically found in this region. Moreover, the Hydrus not only “stents” the canal providing a direct inlet from the anterior chamber to the canal, but also “tensions” the trabecular meshwork and inner wall. Outflow studies have confirmed that this tensioning further enhances outflow. The efficacy results in the U.S. premarket approval trial were as good as any MIGS procedure thus far, while the safety data, as with iStent, were also very favorable, not statistically different from the cataract surgery alone control arm. For example, 77.2% of patients in the Hydrus group achieved a 20% reduction in diurnal washed out IOP compared with 57.8% in the control group (P < .001). The mean change in diurnal IOP at 2 years was 7.6 mm Hg in the phaco-Hydrus group compared with 5.3 mm Hg in the phaco alone group (P < .001). It is noteworthy that the treatment effect of Hydrus relative to control was greater at 2 years than at 1 year.

Some surgeons may be intimidated by the 8-mm design, compared to the 1 mm length of the first generation iStent and the even smaller second generation iStent. However, they may be comforted by the fact that in the U.S. PMA trial, 97% of patients randomized to Hydrus had successful implantation, 86% on the first attempt. Time will tell whether it is better to involve a larger portion of the canal as with Hydrus, or if the very focal and stealth iStent approach is better. The Hydrus, with its more expansive coverage can boast terrific efficacy data at 2 years. Meanwhile, those favoring the more stealth approach might argue that less manipulation may lead to less scarring long term. For now, based on the data from the FDA trials, both approaches are meaningful and welcomed additions to the MIGS portfolio.