Newly Approved Trabecular Microbypass Stent

Cataract Surgery With Trabecular Micro-bypass Stent Implantation in Patients With Mild-to-Moderate Open-Angle Glaucoma and Cataract: Two-Year Follow-up

Craven ER, Katz LJ, Wells JM, Giamporcaro JE; iStent Study Group
J Cataract Refract Surg. 2012;38:1339-1345

The iStent® Is Approved

A new minimally invasive glaucoma surgical device was recently approved by the US Food and Drug Administration (FDA). There is much interest, therefore, in assessing its safety and efficacy.

Dr. Craven, who was an investigator in the clinical trial of the Glaukos iStent® (Glaukos Corporation, Laguna Hills, California); Dr. Katz, who is a consultant to Glaukos and the medical monitor for the clinical trial of the iStent as well as a stockholder; and 2 other employees of Glaukos recently published the results of a prospective, randomized, controlled, multicenter clinical trial involving 29 investigational sites in the United States.

Study Summary

Eyes with mild-to-moderate glaucoma and unmedicated intraocular pressure (IOP) of 22-36 mm Hg were randomly assigned to cataract surgery with the iStent trabecular microbypass stent implantation (stent group) or cataract surgery alone (control group). Patients were followed for 24 months after surgery.

In patients assigned to the stent group, the stent was implanted through the same temporal clear corneal incision used for phacoemulsification and intraocular lens placement. The stent was implanted in the nasal position (3-4 o'clock in the right eye; 8-9 o'clock in the left eye) with the tip of the stent pointing inferiorly.

Study investigators were instructed to add ocular hypotensive medications in a consistent manner in both groups on the basis of IOP, optic nerve, and visual field status, and only if required to control IOP. Specifically, the study protocol stated that medications should be "considered when unmedicated IOP reaches 21 mm Hg or higher." After surgery, patients were examined at 3-7 hours; 1 day; 1-2 weeks; and 3, 6, 12, 18, and 24 months.

The primary efficacy endpoint was an IOP of 21 mm Hg or lower without ocular hypotensive medications at 1 year. The secondary efficacy endpoint was an IOP reduction of 20% or more from baseline at 1 year without ocular hypotensive medications. These outcomes, in addition to the safety profile through 1 year, have now been reported.

The incidence of adverse events was low in both groups through 24 months of follow-up. At 24 months, the proportion of patients with an IOP of 21 mm Hg or lower without ocular hypotensive medications was significantly higher in the stent group than in the control group. Overall, mean IOP was stable between 12 months and 24 months in the stent group (17.0 mm Hg ± 2.8 mm Hg and 17.1 ± 2.9 mm Hg, respectively) but increased in the control group (17.0 ± 3.1 mm Hg to 17.8 ± 3.3 mm Hg, respectively). Ocular hypotensive medication was statistically significantly lower in the stent group at 12 months; it was also lower at 24 months, although the difference was no longer statistically significant.

Viewpoint

In June 2012, the FDA approved the trabecular microbypass stent, known as the iStent. This procedure falls into the category of minimally invasive glaucoma surgery (MIGS).^[1] There is much enthusiasm to find successful MIGS procedures because they do not cause a bleb, an occurrence associated with many potential complications. The iStent is the newest in this group of procedures, and that it can be combined with a cataract-extraction procedure without additional incisions is very appealing. The iStent can also be used for patients with only mild to moderate glaucoma, making it a procedure that not only glaucoma specialists but also comprehensive ophthalmologists can add to their armamentariums.

For this reason, it is imperative to establish the safety and efficacy of the procedure. The study by Craven and colleagues is the largest study conducted to date in the United States with long-term follow-up, and the results were similar to those of previously published studies from Europe and elsewhere.^[2,3,4] Important endpoints of safety as well as efficacy were addressed in this study.

First and foremost, the safety of the procedure must be evaluated. With the advances that have been made in cataract surgery, it has become a relatively safe procedure with good outcomes. By adding another procedure, as simple as it may seem, to cataract extraction, it is necessary to reevaluate the safety and vision endpoints. In this study, there was no difference between the groups in postoperative vision and complications, such as corneal edema (measured by pachymetry) or inflammation. The investigators also analyzed intraoperative complications of the stent implantation, including intraoperative stent removal and replacement, stent malposition, iris touch, and endothelial touch. None of these events were associated with morbidity in patients. Secondary interventions, such as stent repositioning, stent removal and replacement, or Nd:YAG laser for stent obstruction, were needed infrequently.

Overall, despite the statistically significant difference in IOP between the control and iStent groups at 12 months, by 24 months the difference was no longer significant. Even at 12 months, when statistically lower IOP was found, the difference was 0.1 mm Hg, which is unlikely to be clinically significant. Yet, the benefit of this procedure cannot be negated, because this study analyzed only the outcomes of placement of a single stent. Animal model studies have shown an additive effect with placement of multiple stents.^[5]Therefore, given the overall good safety profile, implantation of multiple stents may lead to a more clinically significant decrease in IOP. If further clinical studies confirm this result, we may have a promising procedure to add to our fight against increased IOP.

Abstract