In June 2012, after more than a decade of development and clinical evaluation, the iStent (Glaukos Corp.) received US Food and Drug Administration (FDA) clearance for the management of mild to moderate openangle glaucoma at the time of cataract surgery. This widely anticipated event has the potential to transform how clinicians approach glaucoma management.
Previously, surgical intervention for the treatment of glaucoma was largely reserved for patients in whom medical and laser therapy had failed. With the availability of the iStent, many surgeons now believe earlier surgical intervention is indicated to provide adequate glaucoma treatment in light of patients’ generally poor compliance with prescribed topical therapy, the side effects of glaucoma medications, and the need for 24-hour intraocular pressure (IOP) control.
It appears that the iStent may be a breakthrough among a new class of procedures known as microinvasive glaucoma surgery (MIGS) to arrive in the clinic. This article provides an overview of MIGS procedures that are currently in use or under investigation.
WHAT IS MIGS?
Ike K. Ahmed, MD, of Toronto, Canada, coined the term MIGS several years ago as an acronym for minimally invasive glaucoma surgery, a new class of ab interno microstent procedures. Use of the term exploded, as seen in marketing campaigns for an array of glaucoma procedures, not all of which were considered minimally invasive by glaucoma subspecialists. In fact, MIGS was used to describe almost all glaucoma surgeries other than trabeculectomy or tube shunt procedures, and the terminology became quite confusing.
Consequently, Dr. Ahmed and his colleague Hady Saheb, MD, published a review of MIGS to clarify their thoughts on this surgical space,1 redefining it as microinvasive glaucoma surgery and assigning the following criteria to this classification of procedures:
- Uses an ab interno surgical approach;
- Causes minimal trauma to tissue;
- Provides superior safety and low complication profile compared with traditional filtration surgery;
- Conveys at least modest IOP-lowering efficacy; and
- Enables rapid recovery of patients.
Under this new classification system, MIGS includes trabecular microbypass microstents, suprachoroidal microstents, and ab interno procedures using a subconjunctival surgical approach. Technologies in each category are described below; description of a new goniolens for use with ab interno glaucoma surgery is described in the sidebar on this page.
TRABECULAR MICROBYPASS MICROSTENTS
iStent Inject. In an effort to further automate the implementation of multiple iStents in a single surgical maneuver, Glaukos began developing an injector system that uses a rivet-shaped iStent (Figure 1). This approach is being evaluated in FDA clinical trials and international studies. One-year results demonstrate the ability of two iStents to lower IOP into the midteens and maintain an impressive safety profile.2,3
Hydrus. The Hydrus (Ivantis, Inc.; Figure 2), a 6-mm, flexible scaffold for Schlemm canal, is designed to reestablish aqueous flow to the collector channels. This microstent is injected into Schlemm canal through a clear corneal wound with an ab interno surgical approach. The Hydrus dilates and supports Schlemm canal, targeting approximately 3 clock hours of the collector system. Its design may permit later enhancements to aqueous outflow through the application of Nd:YAG laser energy to three trabecular meshwork windows in the microstent. Early European data (on file with Ivantis, Inc.) demonstrate IOPs in the midteens at 12 months. This device is currently available in Europe and is in an FDA investigational device exemption (IDE) clinical trial in the United States.
Ab interno and efficient canaloplasty. In an effort to increase intraoperative efficiency, iScience Interventional is making an effort to allow surgeons to place a 360º trabecularsuture microstent from an ab interno approach. The overall impact of this surgical approach on IOP lowering and surgical technique has yet to be fully determined.
Efficient canaloplasty seeks to maintain the key elements of canaloplasty but eliminate nonessential steps. The goal of efficient canaloplasty is to offer a procedure that is faster, easier, and more reproducible without compromising efficacy and patient safety. It can be combined with cataract surgery and performed in approximately the same amount of time as standalone cataract surgery. A video of efficient canaloplasty can be viewed at eyetube.net/portals/iscience/index. asp?f=efficient-canaloplasty-by-dr-steven-vold-.
CyPass Micro-Stent. The CyPass Micro-Stent (Transcend Medical; Figure 3) is a supraciliary device composed of a polyimide material. It has a 300-μm lumen and is 6 mm long. The device is implanted with an ab interno approach into the supraciliary space; for a video demonstration, visit eyetube.net/?v=fasmq.
Preliminary results of an ongoing FDA IDE trial have shown a decrease in IOP of approximately 35% and a significantly reduced need for topical glaucoma medications among patients with mild to moderate open-angle glaucoma in the setting of cataract surgery. The procedure is straightforward and has demonstrated an impressive safety profile thus far.4,5 Completion of enrollment in the US IDE trial is targeted for the end of 2012.
iStent Supra. The design of the iStent Supra (Figure 4) is similar to that of the CyPass Micro-Stent. Both use a uveoscleral outflow mechanism to lower IOP. A US IDE trial of the iStent Supra recently began.
Solx Gold Shunt. This device (Solx, Inc.) has thus far been implanted from an ab externo approach; ab interno placement is currently being evaluated.
Aquecentesis (AqueSys, Inc.; Figure 5) is an ab interno subconjunctival-space technology that has the potential to replace trabeculectomy as the filtration surgery of choice for glaucoma surgeons. This procedure uses a porcine–collagenderived, gelatin implant that is soft and flexible when hydrated. It is noninflammatory and may mitigate the problem of implant migration. During the procedure, the tube is injected into the subconjunctival space from an ab interno approach, and its lumen rests 1 to 2 mm into the anterior chamber.
The company continues to assess and refine the dimensions of this product and the surgical technique; however, early postoperative data are encouraging. One year after surgery, IOPs have averaged in the midteens, and patients undergoing incisional glaucoma surgery for the first time have experienced dramatic reductions in their need for glaucoma medications.5 The device is currently undergoing evaluation in an FDA 510(k) protocol to assess its efficacy and safety in refractory glaucoma patients.
The advent of MIGS and the recent approval of the iStent represent potential breakthroughs in the management of glaucoma. Although the surgical procedures comprising the category of MIGS are in their infancy, they offer the hope of improved surgical outcomes, faster visual recovery, and greater safety than traditional filtering surgery. Further study and development of these procedures will almost certainly advance the field.
In addition to further advancement of MIGS, the development of new classes of glaucoma medications and novel drug delivery systems offer promise in improving patient glaucoma care in the years ahead. Furthermore, the utilization of femtosecond laser technologies in glaucoma surgery is also being evaluated. The future of glaucoma management appears bright. I can’t wait to see what is in store for us in 2013.
Steven D. Vold, MD, is a cataract and glaucoma surgery consultant at Vold Vision, PLLC, in Fayetteville, Arkansas. Dr. Vold states that he is a consultant to and investigator for Alcon Laboratories, Inc.; AqueSys, Inc.; Glaukos Corp.; iScience Interventional; Ivantis, Inc.; NeoMedix Corporation; Solx, Inc.; and Transcend Medical. He may be reached at e-mail: email@example.com.
- Saheb H, Ahmed II. Micro-invasive glaucoma surgery: current perspectives and future directions. Curr Opin Ophthalmol. 2012;23(2):96-104.
- Belovay GW, Nagi A, Chan B, et al. Using multiple trabecular micro-bypass stents in cataract patients to treat primary open-angle glaucoma. J Cataract Refract Surg. In press.
- Bacharach J. Results through two years postoperative from prospective, randomized studies of second generation stents and cataract surgery in mild-moderate open-angle glaucoma. Poster presented at: the American Glaucoma Society 22nd Annual Meeting; March 1, 2012; New York, New York.
- Vold SD, Ahmed IK, Craven ER, Ianchulev S. Surgical outcomes and safety of novel supraciliary microstent. Poster presented at: the ASCRS/ASOA Symposium and Congress; April 20-24, 2012; Chicago.
- Vold S. Future devices. Paper presented at: the ACOS Summer Symposium; July 27, 2012; Deer Valley, Utah.