Filling the void in glaucoma therapy

The iStent lowers IOP, reduces medication needs and possesses an excellent safety profile.

By Eric Donnenfeld, MD

As of 2010, open-angle glaucoma (OAG) affected an estimated 2.7 million people in the United States,¹ a number that will only continue to rise in the coming years. In managing this challenging disease, the eye-care community recognized a significant need for additional therapies to manage the challenges this disease presents. To address these issues, Glaukos developed the iStent, a trabecular micro-bypass device. In my estimation, this product represents one of the most successful technology launches that I have witnessed in my career in ophthalmology. Let me explain.

Previously, there was a significant void between topical medications and surgical interventions. Among clinicians, there was the growing awareness that a majority of patients struggled with compliance issues² due to ongoing expense or difficulty using topical medications, allowing damage to the optic nerve to progress. On the other hand, many ophthalmologists did not want to subject their patients to the risk of surgical procedures that may have significant short- and long-term complication rates.

The iStent has helped filled this void with a procedure that arguably does not add significant risk to the cataract procedure while reducing pressure in a significant manner for most patients. Made of surgical-grade titanium, this heparin-coated stent is less than 1-mm long and 0.3-mm high, making it the smallest implantable device for the human body. It bypasses the trabecular meshwork into Schlemm’s canal, restoring the physiologic outflow of aqueous and significantly reducing IOP. In conjunction with cataract surgery, implanting this device is proving exceptionally beneficial for patients with early to moderate OAG.

The iStent has completely changed my personal management, as well as my practice management of glaucoma. It has provided a safer and more effective treatment option than we have had in the past. As an investigator, my experience with the iStent goes back five years. During this time, none of my patients have had a complication that I can relate to the iStent.

Recent studies

Beginning with the stringently designed Pre-Market Approval, multiple clinical trials have demonstrated the safety and efficacy of the iStent in conjunction with cataract surgery in lowering IOP and reducing or eliminating the need for ocular medications.^3-7 Following FDA approval for use in combination with cataract surgery, multiple trials have also demonstrated the efficacy of the iStent as a stand-alone procedure and validated the benefits of placing multiple stents.^8-11

A recent study to evaluate the long-term safety and efficacy of the iStent was conducted in Munich, Germany.¹² This prospective, open-label, non-randomized study evaluated 62 eyes of 43 patients with primary open-angle, pseudo-exfoliation glaucoma, ocular hypertension, or secondary or post-traumatic glaucoma who had one stent implanted during cataract surgery. A total of 41 eyes have been followed for three years postoperatively while follow-up on the remaining 21 eyes is ongoing. Mean baseline IOP was 24.1±6.9 mmHg on a mean of 1.8 medications (±0.9). At 36 months, evaluation of eyes with no secondary surgical intervention demonstrated mean reduction in IOP to 14.9±2.3 mm Hg (n=39). Also at 36 months, medications were eliminated in 74% of eyes and corrected distance visual acuity was 20/40 or better in 93% of eyes.

While a single iStent can make a significant improvement for most OAG patients, sometimes greater lowering of IOP is needed. The placement of a second iStent enhances the benefit. My colleagues and I completed a prospective pilot study¹³ that evaluated the three-year safety profile and IOP reduction following placement of two trabecular microbypass stents in phakic and pseudophakic subjects with OAG not controlled on preoperative medication. Thirty-nine qualified subjects with preoperative unmedicated IOP between 22 mmHg and 38 mmHg received two stents. The mean IOP at 36 months was 15.2 mmHg. The subjects sustained a mean IOP decrease of 9.1±2.7 mmHg (95% CI 8.0 mmHg, 10.14 mmHg), or 37% IOP reduction, from the unmedicated baseline IOP.

When compared to the preoperative medicated IOP, the subjects’ mean reduction at month 36 was 5.5±2.7 mmHg (95% CI 4.5 mmHg, 6.6 mmHg), or a 26% reduction. Both results were highly significant (P<0.001). Regarding complications, one case of early postoperative hyphema resolved at 1 week. No other postoperative adverse events were attributed to stent implantation.

In my practice, the general guideline revolves around the concept that if the patient is on one medication I will implant one iStent and in most circumstances I can usually eliminate that medication. If the patient is on two medications, I generally try to use two iStents.

A familiar surgical technique

Surgical technique plays a significant role with the iStent but is one that most general ophthalmologists will be comfortable performing. The stent is preloaded in a single-use, sterile applicator and is implanted through the same small, temporal, clear corneal incision used for phacoemulsification. When performed as a stand-alone procedure the stent can be implanted through a 1.5-mm incision. (The iStent has FDA approval for implant during cataract surgery.)

Figure 1. iStent inserter placing the device in trabecular meshwork.

As with all procedures, there is a slight learning curve in finding the right angles and tilt positions, applying the correct amount of pressure, and using the equipment. It takes a moderate amount of manual dexterity and comfort. However, it is well within the purview of the great majority of cataract surgeons. It is a very safe procedure to perform. There is really no downside to performing this procedure. Eliminating the burden of topical medications and their effect on the ocular surface is greatly beneficial for patients.

Conclusion

In summary, the iStent, the first MIGS device routinely used in ophthalmology, allows general ophthalmologists as well as glaucoma specialists to treat patients with mild to moderate glaucoma safely and effectively. It has opened up a new era of cataract surgery that brings the general ophthalmologist into glaucoma surgery, a development that is good for patients and surgeons alike.

Figure 2. iStent in place in trabecular meshwork.

The iStent is an instrumental part of my surgical armamentarium for improving cataract surgery outcomes. Patients’ expectations are rising and our ability to meet these expectations is what makes us successful in practice. This refractive cataract surgical procedure gives patients that great quality vision that they need and expect in a painless and safe manner, while also reducing or eliminating the burden of glaucoma medications. Providing this is a significant advantage and patients greatly appreciate the effort and the expertise of the doctors who go that extra yard to make their quality of life better. OM

REFERENCES

About the Author
	Eric Donnenfeld, MD, FACS, is a board certified ophthalmologist and experienced corneal surgeon. He is a professor of ophthalmology at NYU and a trustee of Dartmouth Medical School. Dr. Donnenfeld is a consultant for Alcon, Allergan, AqueSys and Glaukos. He may be reached via e-mail at: ericdonnenfeld@gmail.com.