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Growing number of minimally invasive techniques expands options for glaucoma patients
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 Richard L. Lindstrom |
Glaucoma surgery can be classified in many ways.
One classification system that is useful to me describes the procedure as minimally invasive glaucoma surgery (MIGS) vs. a more invasive alternative. While the invasiveness of a procedure is a subjective determination, most of us can differentiate between the two alternatives, and some may actually be moderately invasive. The second classification system considers the mechanism of action of the pressure lowering. In this system, we have procedures that move aqueous fluid through the sclera (transscleral) from the anterior chamber into the subconjunctival space, from the anterior chamber into the suprachoroidal space, and from the anterior chamber into Schlemm’s canal. In each of these categories, there are procedures that can be classified as MIGS vs. their more invasive alternatives. In addition, we have a procedure, cyclophotocoagulation, that reduces aqueous production and comes to the surgeon in a MIGS option as well.
A few personal thoughts on each. The classical ab externo trabeculectomy and tube shunt are, in my opinion, definitely not minimally invasive. They both represent 30 to 60 minutes of incisional surgery associated with significant tissue manipulation and bleeding and require a high level of surgeon skill, both during surgery and in the postoperative period. Antimetabolites are frequently required, as are postoperative manipulations such as massage or needling. Initial success rates are high, but according to the Tube Versus Trabeculectomy Study, 15.1% of tubes and 30.7% of trabeculectomies fail by 3 years postoperative. In addition, this same study reports that postoperative complications number 39% in the tube surgery patients, with 22% classified as serious, and 60% in the trabeculectomy patients, with 27% considered serious. Clearly, this is not minimally invasive surgery, and the decision to perform this procedure requires careful thought and informed consent, because some of the complications, such as an increased risk of bleb infection, last a lifetime. On the positive side, large reductions in IOP were achieved with both tube shunt and trabeculectomy, measuring approximately 13 mm Hg in each group with the use of an average 1.2 topical medications as an adjunct. No doubt, when low pressures are targeted, these two procedures are preferred. Of interest is the fact that tube shunts generated equivalent pressure drops to trabeculectomy with a lower complication rate and less failure at 3 years. These findings have resulted in an increased utilization of tube shunts by many glaucoma specialists.
The Ex-PRESS shunt from Alcon has been developed with the promise of making trabeculectomy less invasive and more reproducible in outcome. In addition, AqueSys, a startup company in California, is attempting to take transscleral filtration into the MIGS category. In regard to movement of aqueous into the suprachoroidal space, cyclodialysis has been abandoned by most because of a high incidence of complications, including bleeding and hypotony.
Two companies in California, Transcend and Glaukos, are developing new minimally invasive approaches to move fluid into the suprachoroidal space safely and effectively. Pressure drops can be significant with this approach, and early results are promising. Glaukos has developed the iStent, which when placed into the trabecular meshwork appears capable of reducing IOP and medication burden in a physiologic and minimally invasive fashion. Canaloplasty (iScience Interventional), perhaps an example of moderately invasive glaucoma surgery, is showing promise as well. Endocyclophotocoagulation, perhaps also moderately invasive, offers us a safer way to reduce aqueous production in select cases.
For the patient with cataract, phacoemulsification alone may represent a highly effective member of the MIGS grouping, with a pressure drop of 8.4 mm Hg when starting with a patient with a preoperative pressure off medications near 25 mm Hg in a recent prospective clinical trial (Glaukos U.S. Food and Drug Administration trial). The other members of the MIGS class show promise of being synergistic and additive in the patient with combined cataract and glaucoma.
Considering the daunting regulatory barriers facing any company attempting to develop a new device in America, we are fortunate indeed to have this many companies pursuing a better, less invasive way for us to treat our patients with glaucoma who require surgery. Many of the MIGS procedures under study in the U.S. are currently being commercialized in Europe, Asia and Latin America. I predict that MIGS will join MICS (minimally invasive or microincision cataract surgery) as a regular in our therapeutic armamentarium in the next decade.
If the risks of MIGS are low enough and the benefits great enough, it is possible to imagine a time when MIGS might represent an elective option for the individual motivated to a lifestyle independent of the daily nuisance of glaucoma drop application. MIGS might then join oculoplastic surgery and cornea- and lens-based refractive surgery as a patient-pay quality-of-life option for the motivated and fully informed patient. I believe such an option would be welcomed by many of the 78 million baby boomers now dealing with the handicap of glaucoma and the difficult challenge of complying with the daily medication regimens required for proper therapy.