Within the growing microinvasive glaucoma surgery (MIGS) category, a new option is now available. Glaukos, the first company to bring a MIGS device to market with the iStent Trabecular Micro-Bypass, recently received FDA approval for the iStent inject. The iStent inject has a redesigned stent and a straightforward implantation approach. It includes 2 stents in a single injector. Recent data shared at the American Society of Cataract and Refractive Surgeons annual meeting indicate that the iStent inject is likely to further grow the surgical treatment of mild to moderate glaucoma.

Designed for Success

The iStent inject is the smallest medical device believed to be implanted in humans. At just 0.3 mm in diameter and 0.4 mm long, the heparin-coated titanium stent is one-third of the size of the first iStent. In contrast to the first generation iStent, which is inserted circumferentially, the iStent inject is inserted directly through the trabecular meshwork, perpendicular to the canal (Figure 1). It has multiple outlet lateral lumens to provide an exit route for aqueous humor from the anterior chamber into Schlemm’s canal.

Long-term safety and efficacy studies of the iStent demonstrated that it effected significant and sustained reduction of both IOP and medication use with an excellent safety profile.¹ Further exploratory studies confirmed that placement of additional stents served to titrate therapy, providing greater IOP reduction while maintaining the same superior safety profile.^2,3 With this in mind, the iStent inject includes 2 stents preloaded in an elegant injector.

The injector is placed perpendicularly to the trabecular meshwork in the nasal quadrant and the first stent is deployed. The injector is moved approximately 2 to 3 clock hours away and the second stent is deployed. Theoretically, the 2 stents combine to provide access to nearly 6 clock hours of the trabecular meshwork, significantly increasing the probability that the stents are close enough to a collector channel for aqueous to efficiently drain from the anterior chamber.

Pivotal Trial Design

The FDA pivotal trial for the iStent inject included 505 patients randomized to receive phacoemulsification alone (n=118) or phacoemulsification plus iStent inject (n=387). Conducted at 41 investigational sites across the United States, all patients underwent medication wash-out at baseline, at year 1, and at year 2. The demographics and disease characteristics were balanced between the groups, with mean medicated and unmedicated baseline IOPs of 17.±3.0 mmHg and 24.8±3.3 mmHg respectively in the iStent inject + phacoemulsification group and 17.5±2.8 mmHg and 24.5±3.1 mmHg in the phaco-only group.

At 24 months, the iStent inject + phaco group had a mean reduction in IOP of 7.0 mmHg, while the phacoemulsification-only group saw a mean 5.4 mmHg reduction in IOP. The iStent inject provided significantly greater IOP reduction than the phacoemulsification-only control group, with 75.8% of eyes meeting the desired endpoint of ≥20% reduction in unmedicated IOP. The impact of the device on quality of life can be seen with the reduction in medications. 84% of patients that received iStent inject were medication free at the 23-month time point, prior to wash-out. The safety profile of the iStent inject is favorable and comparable to cataract surgery alone.

Managing Glaucoma

It is an accepted fact that as the population ages, the incidence of glaucoma in increasing. Thankfully, we have improved diagnostic capabilities to detect the disease earlier, before irreparable damage is done to the optic nerve. While this is good news, it also means that patients have many years of management of a chronic disease ahead of them. It is important that we have very safe options, so that we can continue to control IOP and mitigate the disease process without subjecting patients to severe adverse events or burdensome drop schedules. I believe that iStent inject is an ideal early step in glaucoma management. It provides a significant reduction in IOP without unacceptable risks to visual acuity. The FDA trial suggests that patients receiving iStent will have lower IOP and fewer medications. If they eventually need additional treatment, no options have been removed from consideration due to the stent. As physicians, we are well aware that glaucoma is a disease that is managed, not cured. iStent inject is an excellent tool for doing just that. GP

References

1. Neuhann TH. Trabecular micro-bypass stent implantation during small-incision cataract surgery for open-angle glaucoma or ocular hypertension: long-term results. J Cataract Refract Surg. 2015;41(12):2664-2671.
2. Belovay GW, Naqi A, Chan BJ, Rateb M, Ahmed II. Using multiple trabecular micro-bypass stents in cataract patients to treat open-angle glaucoma. J Cataract Refract Surg. 2012;38(11):1911-1917.
3. Katz LJ, Erb C, Carceller Guillamet AC, et al. Prospective, randomized study of one, two, or three trabecular bypass stents in open-angle glaucoma subjects on topical hypotensive medication. Clin Ophthalmol. 2015;9:2313-2320.

Thomas W. Samuelson, MD, is an adjunct associate professor at the University of Minnesota, Minneapolis and attending surgeon at Minnesota Eye Consultants/Phillips Eye Institute/Hennepin County Medical Center, in Minneapolis, Minnesota. Dr. Samuelson reports consultancy to Alcon, Aerie, AqueSys, Glaukos, Inotek, Ivantis, Johnson & Johnson Vision, and Transcend Medical. Reach him at twsamuelson@mneye.com.