Microinvasive glaucoma surgery has taken off since the iStent Trabecular Micro-Bypass (Glaukos) received FDA approval in 2012. Many companies and physicians are dedicated to increasing aqueous outflow to lower IOP via a small implant. Glaukos’ iStent and iStent Inject (the latter in US clinical trials) circumvent the trabecular meshwork and inner wall of Schlemm canal to reestablish outflow. The advantages of the iStent are its smallness and its ease of insertion once the device is positioned and the surgeon has a good view. It is unknown at this time if two stents will provide a lower IOP than one, but preliminary evidence suggests that two devices and one eye drop can achieve an IOP of less than 15 mm Hg.1
The canal might benefit from dilation, however, and the Hydrus (Ivantis) exploits that option by dilating several clock hours of the canal after entering the eye through the trabecular meshwork. This technology is the subject of an FDA clinical trial, and several trials across the globe are evaluating the efficacy of the device. There are few published reports on the Hydrus’ efficacy, but the preliminary data are promising.
The suprachoroidal and supraciliary space (the uveoscleral outflow system) is also being investigated for microinvasive glaucoma surgery. IOP values of 12 or 14 mm Hg might be achievable because of the lack of outflow resistance from the collector channels and the episcleral venous pressure. European registry data for the CyPass Micro-Stent (Transcend Medical) showed that patients with uncontrolled IOP achieved over a 35% reduction in IOP after the device’s implantation.2 The uveoscleral outflow system might also work better than the canal system in patients with obstructions to the trabecular meshwork or those who have poor vascularity and a lack of aqueous veins.
The Xen (AqueSys) implant uses a porous gel to slow the flow of aqueous in the hole the device creates. As aqueous moves into the subconjunctival space, it creates a bleb. The gel allows for a more controlled outflow. Data are not yet available, but the concept is appealing.
For now, it appears that these implants, once approved, will fit nicely into daily practice.
This piece is adapted with permission from the March/April 2014 issue of Glaucoma Today.
E. Randy Craven, MD, is the chief of glaucoma at King Khaled Eye Specialist Hospital in Riyadh, Saudi Arabia, and is an associate professor at Johns Hopkins University in Baltimore. He is a consultant to Ivantis and Transcend Medical. Dr. Craven may be reached at (303) 748-5102; erandycraven@gmail.com.
- Solomon KD. Randomized trial of 1, 2, or 3 trabecular microbypass stents and travoprost in open-angle glaucoma controlled on two medications. Paper presented at: The ASCRS Annual Meeting; April 20-24, 2012; Chicago, IL.
- Hoeh H, Ahmed II, Grisanti S, et al. Early postoperative safety and surgical outcomes after implantation of a suprachoroidal micro-stent for the treatment of open-angle glaucoma concomitant with cataract surgery. J Cataract Refract Surg. 2013;39(3):431-437.
