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A trabecular bypass micro stent (iStent, Glaukos) was developed to restore fully natural physiologic outflow in glaucomatous eyes by allowing flow of aqueous from the anterior chamber into Schlemm's canal.
Brookville, PA-Results from a European study indicate that ab-interno implantation of a trabecular micro-bypass stent (iStent, Glaukos) in eyes with open-angle glaucoma undergoing simultaneous cataract surgery results in safe and effective IOP lowering, according to Louis D. "Skip" Nichamin, MD.
"Experience in this study showed the stent could be easily implanted via the same small temporal clear corneal incision used for phacoemulsification without inducing additional ocular trauma, and to date, the stent appears to be highly biocompatible and working effectively," said Dr. Nichamin, medical director, Laurel Eye Clinic, Brookville, PA.
"The procedure has been associated with significant reductions in IOP and reduced patient reliance on topical medications while the complication profile is related more to ocular surgery in general than to the implant itself," he said. "Foreseeably, the [stent] also could be used in phakic patients with mild-to-moderate glaucoma to control IOP and reduce the drug burden and compliance-related problems for these individuals."
The stent aims to reduce IOP in glaucomatous eyes by restoring fully developed natural physiologic outflow. It is implanted through a clear corneal incision, directly in Schlemm's canal, where it facilitates aqueous outflow from the anterior chamber into the canal, ostensibly by bypassing the major obstruction in the meshwork and using the natural flow control mechanism within the collector ducts and episcleral veins.
"The ab-interno approach avoids conjunctival scarring and a filtering bleb," Dr. Nichamin said. "Therefore, it obviates the complications traditionally associated with filtering procedures and subconjunctival drainage tubes. By sparing the conjunctiva, it also preserves all future therapeutic and surgical options for glaucoma patient care."
The stent is constructed of a heparin-coated, medical grade titanium that is highly biocompatible, very strong, and corrosion-resistant. It features barbs that secure it within Schlemm's canal, and its lumen is sized to allow "just enough" aqueous flow to accommodate aqueous production and reduce IOP while avoiding hypotony.
In Europe, where the stent is commercially available, two or three stents have been implanted in a single eye to achieve further lowering of IOP.
The stent is delivered through a 1- to 1.5-mm clear corneal incision that is constructed 180° away from where the stent will reside. Holding a gonioprism in one hand, and an introducer with the preloaded stent, the surgeon introduces the device through the corneal incision, engages and perforates the meshwork, and advances the device so that its inlet end stents the meshwork and opens into the anterior chamber. Once in position, the stent is released by depressing a button on the introducer with the index finger.
The appearance of a small amount of reflux hemorrhage indicates correct positioning within Schlemm's canal. Once implanted, the stent is stable and does not migrate even with removal of viscoelastic.
"It would be reasonable to say there is a brief learning curve for the procedure, which for me involved working with a gonioprism and learning to gauge the depth," Dr. Nichamin said. "I found it helpful to actually nudge the angle to judge my position, and then proceed to engage the meshwork and work the stent into the canal."
Implantation of the stent in combination with phacoemulsification is also being investigated in an FDA study. Enrollment has been closed and data are expected soon.
Outcomes are available from the multicenter European Combo Cataract where the stent was implanted in eyes undergoing simultaneous phacoemulsification via a clear corneal incision. The study enrolled 58 patients and results were analyzed for 52 eyes that completed at least 12 months of follow-up.
Compared with baseline, IOP was reduced by a mean of 18% on the first day after surgery and 17.5% at month 12. Mean reduction from baseline at interim visits varied between 14.2% and 25.3%. The patients also had a reduction in average medication use from 1.7 preoperatively to 0.6 at 12 months.
The primary efficacy endpoint for the study is proportion of patients achieving IOP ≤18 mm Hg with or without medications. At 12 months, 45% of patients achieved this goal.