With the release of the iStent Trabecular Micro- Bypass Stent (Glaukos Corporation) for clinical use in the United States after a decade of basic science research and clinical trials, it remains to be seen how quickly ophthalmologists will adopt this surgical option. Clinicians will weigh a number of factors during their assessment of a new operation for their glaucoma patients. Already, practitioners have adopted other relatively recent glaucoma procedures such as deep sclerectomy, viscocanalostomy, canaloplasty, the Ex-Press Glaucoma Filtration Device (Alcon Laboratories, Inc.), Trabectome surgery (NeoMedix Corporation), and endoscopic cyclophotocoagulation (E2 Microprobe Laser and Endoscopy System; Endo Optiks) to varying degrees. Can one predict how the iStent will be used in the coming years?

ADVANTAGES

The most common glaucoma operations, trabeculectomy and tube shunts, require the creation of a subconjunctival filtering bleb with well-known accompanying risks. Hypotony can lead to suprachoroidal hemorrhage, choroidal effusions with flat anterior chambers, and maculopathy. Bleb infections can result in endophthalmitis. Persistent diplopia and corneal edema with tube shunts may require further surgery.

Among the compelling attributes of the iStent are that it lowers IOP without a filtering bleb, restores the physiological outflow pathway, requires a short operative time, is easily combined with cataract surgery, is associated with a minimal complication rate, has a limited need for additional instrumentation, and has the support of a series of published trials.

The fundamental pathology of open-angle glaucoma is an abnormally high resistance to aqueous outflow. The iStent was designed to circumvent the resistance of the trabecular meshwork and juxtacanalicular tissue and to connect the anterior chamber with Schlemm canal. The safety profile through 2 years of the device combined with cataract surgery appears to be similar to that encountered with cataract surgery alone.1,2 The stent is inserted through a clear corneal incision, making its implantation an easy companion procedure to phacoemulsification. The pivotal US trial for FDA approval compared iStent plus cataract surgery with cataract surgery alone in cases of early to moderate glaucoma. Samuelson and coworkers noted that, with the first treatment option, IOP was more easily controlled with fewer medications to reach the targeted levels of IOP reduction.1 Craven and colleagues noted a treatment effect through 2 years.2 Other articles have suggested that the device alone may lower IOP and that multiple stents have an even more profound IOP-lowering effect.3

BARRIERS

Despite the iStent's virtues, there will be roadblocks to its adoption. By their training and experience, physicians are wary of “advances” in their field. They have a sense of comfort with existing therapies, the advantages and disadvantages of which they have gleaned from personal experience. Similarly, many patients prefer procedures familiar to their surgeon. Understandably, a lot of them may cringe upon hearing that they will be among the first to undergo an operation that is new to their surgeon.

The FDA approved the iStent for use in patients with mild to moderate glaucoma who need cataract surgery. Obviously, this eliminates all those patients who require glaucoma surgery but do not require cataract surgery and those who have advanced glaucoma. Although surgeons often feel most comfortable performing a newly introduced operation on patients with far advanced disease, the iStent will be used at an earlier stage.

The technique for placing the stent in the eye is a novel approach that demands additional training, even for experienced ophthalmic surgeons. Successful implantation entails a series of educational steps. First, surgeons must clearly understand the angle's anatomy, because accurate cannulation of Schlemm canal through the trabecular meshwork requires identification of the trabeculum, the pigmentation of which varies among patients. Second, they must master intraoperative gonioscopy with a goniolens (eg, Swan-Jacob [Ocular Instruments, Inc.]) in order to view the angle during the device's insertion. Third, the surgical team has to properly position the patient's head and body at an angle and tilt the operating microscope for a clear view. Fourth, surgeons must become acquainted with the insertion device that comes preloaded with the iStent. Finally, they must learn new hand positioning and instrument handling.

Glaukos has recognized the importance of thoroughly training surgeons before allowing them to use the iStent. The release of the device will be regulated, with multiple waves of surgeons being trained at different times via online courses and wet lab instruction.

The cost of the device and reimbursement policy will also influence the ophthalmic community's adoption of the iStent.

CONCLUSION

Slow initial use of the iStent is to be expected. If surgeons are adequately trained and prepared to implant the device, and if their results with the procedure match or exceed those in the clinical trials, then a rapid acceleration in the stent's use will almost certainly follow. A cautious approach is reasonable, although it is deeply to be hoped that this device and other microinvasive glaucoma surgeries will provide ophthalmologists with another viable option for treating patients with this disease.

L. Jay Katz, MD, is director of the Glaucoma Service at the Wills Eye Institute and professor of ophthalmology at Thomas Jefferson University in Philadelphia. He is a medical monitor for and consultant to Glaukos Corporation. Dr. Katz may be reached at (215) 928-3197; ljkatz@willseye.org.

  1. Samuelson TW, Katz LJ, Wells JM, et al; US iStent Study Group. Randomized evaluation of the trabecular microbypass stent with phacoemulsification in patients with glaucoma and cataract. Ophthalmology. 2011;118(3):459-467.
  2. Craven ER, Katz LJ, Wells JM, Giamporcaro JE. Cataract surgery with trabecular micro-bypass stent implantation in patinets with mild-to-moderate open-angle glaucoma and cataract. Two-year follow-up. J Cataract Refract Surg. 2012;38:1339-1345.
  3. Belovay GW, Naqi A, Ahmed IIK. Using multiple iStents in cataract patients to treat primary open angle glaucoma. Poster presented at: The 20th Annual AGS Meeting; March 4-6, 2010; Naples, FL.