InnFocus MicroShunt® Glaucoma Drainage Implant
Despite the litany of risks and bleb-related issues patients must contend with, there are many surgeons who do not share my disdain for trabeculectomy. To their way of thinking trabeculectomy is a well-established glaucoma procedure that just needs a little “fine tuning”. The InnFocus MicroShunt® may be just what they are looking for.
InnFocus MicroShunt®: What Is It?
The InnFocus MicroShunt® is an 8.5mm long flexible tube made of a biocompatible material called SIBS. It has a very small lumen (70 micrometers) that acts to restrict the flow from the anterior chamber into the subconjunctival space. The tube is inserted through a scleral flap into the anterior chamber. It has tiny fins on the outside of it that keep the tube from migrating further into the eye after it has been implanted.
IMAGE CREDIT: InnFocus Inc. InnFocus Microshunt™ [Internet]. 2015 [cited 2015 Jun 10]. Available from: http://innfocusinc.com/index.php/microshunt/
CAUTION: INVESTIGATIONAL DEVICE. LIMITED TO INVESTIGATIONAL USE IN THE UNITED STATES.
In general surgical implantation of the InnFocus MicroShunt® is faster and potentially easier than trabeculectomy. Because there is no need to create a peripheral iridectomy (removal of iris tissue) there should be less post-operative inflammation. Additionally, as the size of the lumen of the InnFocus MicroShunt® was chosen in order to achieve a steady rate of flow from the eye, both early IOP spikes and hypotony should be encountered less frequently than with trabeculectomy. The need for antimetabolites (Mytomicin-C or 5-FU), however, is still required in order to ensure long-term survival of the bleb.
How Well Does the InnFocus MicroShunt® Appear to Work?
Fortunately, there are a number of ongoing long-term studies evaluating the effect of the InnFocus MicroShunt® with use of Mitomycin-C (MMC). To date these have been small in size with only preliminary results presented at conferences rather than published in peer-reviewed journals. Nonetheless, the available results can at least give us a peek into how this device may perform.
2014 European Glaucoma Society Congress (EGSC)
Three year results of the InnFocus MicroShunt® implanted alone or with cataract surgery were presented at the 2014 European Glaucoma Society Congress (EGSC) in Nice, France. There were 43 eyes included in the study: 28 eyes underwent placement of the InnFocus MicroShunt® alone and 15 eyes underwent implant placement at the time of cataract surgery. Only 17 of these eyes had been followed for a full three years.
Mean (average) IOP was reduced by over 50% from just under 24mmHg to just under 11mmHg. Average glaucoma medication use decreased from 2.8 to 0.4 drops. An outstanding 94% of study patients were off all glaucoma drops at the end of the study period! Interestingly (and unlike what would be expected with trabeculectomy), cataract surgery did not seem to alter the IOP outcome. Importantly, none of the patients in this study required additional trabeculectomy or glaucoma drainage device surgery.
2015 meeting of the American Society of Cataract and Refractive Surgery (ASCRS)
Three-year data were also presented at the 2015 annual meeting of the American Society of Cataract and Refractive Surgery (ASCRS). This was a small study of “trabeculectomy-stage patients who failed maximum tolerated glaucoma medication” which I can only imagine means that their glaucoma was moderate to advanced with a likely IOP target in the low teens. The study was neither randomized nor controlled: 14 eyes underwent placement of the InnFocus MicroShunt® alone and 9 eyes underwent implant placement at the time of cataract surgery. It appears that these patients may have been a subset of the patients presented at the 2014 EGSC.
The three-year results presented at ASCRS were pooled so it is not possible to determine how much IOP lowering may have been due to the cataract surgery. Mean (average) IOP was reduced by over 50% from just under 24mmHg to just under 11mmHg. Average glaucoma medication use decreased from 2.4 to 0.5 drops. The percentage of patients who achieved an IOP lowering of at least 20% with a final IOP below 22mmHg was 95% including those who required drop use and 73% without use of drops.
One thing about both of these studies, however, really irks me: the definition of success as ”IOP<=21mmHg”. Actually, many studies commonly use this definition of success so why does this bother me? Because there simply is no glaucoma surgeon who would consider an IOP of 21mmHg a “success” after trabeculectomy. All this definition of success does is make it impossible to know how well the surgery will actually perform out in the “real world”. Recall that the most recent study only included “trabeculectomy-stage patients” who likely required an IOP in the low teens to adequately control their glaucoma. Isn’t control of glaucoma what the reasonable person would consider success? According to data presented by InnFocus, 82-85% of patients achieve an IOP below 15mmHg with or without the use of drops. That is data I would like to see confirmed in a peer-reviewed publication.
InnFocus MicroShunt® versus Trabeculectomy
A separate three-year head-to-head comparison with trabeculectomy is currently under way. Shortly after the results have been made public I will review them here: InnFocus Microshunt versus Trabeculectomy, 3-Year Results
NOTE: The results have not yet been reviewed. If you’d like to be informed of these results as well as other advances in glaucoma treatments sign up for email announcements HERE:
Risks of Implanting the InnFocus MicroShunt®
Implantation of the InnFocus MicroShunt® is essentially a modified trabeculectomy that results in a bleb. As such, it at least in theory shares the risks of trabeculectomy. In the studies mentioned above common early post-operative complications included transient hypotony (12-13%) and choroidal effusion (4-9%), the latter likely related to hypotony. Additional early complications reported at the EGSC included elevated IOP requiring treatment (12%), hyphema (12%), corneal swelling (9%), and blockage of the stent (2%). Long-term these patients appeared to do well with “no sight-threatening long-term adverse events”. Also of note is that at least according to data presented by InnFocus, no patients developed a cataract after this procedure. Development of a cataract is a very common and expected complication of trabeculectomy.
The InnFocus MicroShunt® may very well be what we were hoping the EX-PRESS® Glaucoma Filtration Device would be: a faster, safer alternative to trabeculectomy. Early results are promising. As with the EX-PRESS® Glaucoma Filtration Device, however, early results cannot provide us with the long-term experience needed to determine what unanticipated issue might arise. I am cautiously optimistic that this device will meet expectations and, if so, that it will be approved by the FDA.
- Riss I, et al. Evaluation of the Safety and Efficacy of the InnFocus MicroShunt Implanted Alone or Combined with Cataract Surgery: Three year Follow-Up. Poster presented at: EGS 2014. European Glaucoma Society Congress; 2014 Jun 7-11; Nice, France.
- Batlle JF, et al. Novel Aqueous Humor Microshunt Implanted Alone or Combined With Phacoemulsification: 3-Year Follow-up. Paper presented at: ASCRS 2015. ASCRS-ASOA Symposium & Congress; 2015 Apr 17-21; San Diego, CA.
- Trenary R. InnFocus. Presented at: OIS@AAO 2014. Ophthalmology Innovation Summit; 2014 Oct 16; Chicago, IL.
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About the Author: David Richardson, MD
Medical Director, San Marino Eye
David Richardson, M.D. is widely recognized as one of the top cataract and glaucoma surgeons in the US and is among an elite group of glaucoma surgeons in the country performing the highly specialized canaloplasty procedure. Morever, Dr. Richardson is one of only a few surgeons in the greater Los Angeles area that performs Micropulse® "Cyclophotocoagulation" (MP3) glaucoma laser surgery. Dr. Richardson graduated Magna Cum Laude from University of Southern California and earned his Medical Degree from Harvard Medical School. He completed his ophthalmology residency at the LAC+USC Medical Center/ Doheny Institute. Dr. David Richardson is also an Adjunct Assistant Professor of Clinical Ophthalmology at Keck School of Medicine of USC. Twice weekly, he treats veterans at the VA Greater Los Angeles Veterans Healthcare System.