FDA Panel Recommends Premarket Approval for Ocular Stent

Emma Hitt, PhD

August 02, 2010

August 2, 2010 — The Glaukos iStent Trabecular Micro-Bypass Stent was determined to have benefits outweighing its risks by a US Food and Drug Administration (FDA) ophthalmic devices advisory panel on July 30.

The panel was convened to discuss the premarket approval application of the stent for its use in conjunction with cataract surgery to reduce intraocular pressure (IOP) in mild to moderate open-angle glaucoma treated with ocular hypotensive medication.

According to background information from the FDA, the stent is designed to "increase aqueous outflow by shunting aqueous humor from the anterior chamber to Schlemm's canal, bypassing the trabecular meshwork; thus, no filtering bleb is formed."

The prospective, randomized study used by the FDA as the primary basis for the evaluation of safety and effectiveness included 240 eyes (117 treatment eyes and 123 control eyes). In addition, 50 participants were included for the evaluation of safety.

Study duration was 2 years, with primary effectiveness endpoints evaluated at 12 months postoperatively. Subjects were diagnosed in the study eye with mild to moderate open-angle glaucoma or with pseudoexfoliative and pigmentary glaucoma.

The primary endpoint was the proportion of subjects with IOP of 21 mm Hg or less without use of antiglaucoma medication at 12 months. Of the patients in the treatment group, 68.1% met the primary endpoint compared with 49.6% in the control group (P = .003). The mean IOP in the treatment group at 12 months was 19.2 mm Hg compared with 21.1 mm Hg in the control group.

No statistically significant difference between groups 24 months postoperatively was observed.

Stent-related adverse events were infrequent. Stent obstruction by iris, vitreous, fibrous overgrowth, fibrin, blood, and so on was noted in 4% of patients, and stent malposition was noted in about 3%.

Stent-related secondary surgical interventions were reported in 5 participants (3 with stent repositioning, 1 with stent removal and replacement, and 1 with laser iridoplasty) to resolve stent obstruction or malposition observed by investigators in the early postoperative period.

The 8-member panel, led by corneal specialist Joel Sugar, MD, from the University of Illinois, Chicago, voted 7 to 1 in favor (no abstentions) that the stent was "reasonably safe" for use in this setting. With respect to efficacy, the panel voted 6 to 2 in favor (no abstentions) of the statement that there is "reasonable assurance" that the device is effective in reducing IOP. Regarding the question, "Do the benefits outweigh the risks?" the panel voted 7 to 1 in favor (no abstentions).

Panelist Mae O. Gordon, PhD, from the Washington University School of Medicine, in St. Louis, Missouri, voted "no" for adequacy of safety information, especially in the long term. "The cumulative damage due to endothelial cell loss is beyond the scope of the immediate study but very important for integrity of the cornea," she said as rationale for her voting.

Stephen D. McLeod, MD, from the University of California–San Francisco, voted "no" on the issue of efficacy because of the issue of whether this device would be relevant for a "significant portion of the population."

Alice Y. Matoba, MD, from Baylor College of Medicine, in Houston, Texas, voted "no" in response to the question of whether the benefits outweighed the risks. "I had concerns about the fact that there were no strict criteria regarding the rescue step in the testing," she said. According to Dr. Matoba, patients in the study group who had IOP greater than 21 mm Hg but also had progressive field change were not rescued and perhaps should have been. "I just did not feel comfortable that the efficacy had been proven, although I do not have concerns about the safety," she added.

Jason Connor, PhD, from Berry Consultants, in College Station, Texas, voted yes to all 3 questions, noting that "I think this could be another option for ophthalmologists to treat this disease, and the more options the better perhaps."