Implants lower intraocular pressure, reduce medication

October 15, 2010

The implantation of multiple trabecular micro-bypass implants in Schlemm's canal following phacoemulsification successfully and significantly reduced IOP for 12 months after implantation as well as the number of medications required to maintain the target IOP.

Toronto-The implantation of multiple trabecular micro-bypass implants (iStent, Glaukos) in Schlemm's canal following phacoemulsification successfully and significantly reduced IOP for 12 months after implantation, as well as the number of medications required to maintain the target IOP.

The trabecular stent is passed through the inner wall of Schlemm's canal during what Dr. Ahmed described as a minimally invasive surgery, and the device is a possible alternative to current surgical options.

In glaucoma, he explained, 50% to 90% of aqueous outflow resistance is in the trabecular meshwork. Although a single trabecular bypass implant can alleviate the resistance, multiple bypasses may be even more effective.

The implant is 1 mm long, has a self-trephinating tip, and is made of heparin-coated, surgical-grade titanium. The device has a 0.3-mm snorkel that goes into the anterior chamber, and it comes loaded in an applicator for insertion into Schlemm's canal.

A study of the effectiveness of implantation of a single stent showed that, after 18 months, IOP decreased a mean of 5 mm Hg or 22% and the mean number of medications needed by patients to control IOP decreased by 1.2 medications.

In another trial, use of a single stent was compared with multiple stents. This study was based on the rationale that lack of circumferential flow limits IOP reduction with one bypass. Use of multiple bypasses further reduced the IOP, likely by enhancing collector channel proximity to the bypass.

Dr. Ahmed conducted a prospective study in which 25 consecutive patients were enrolled. The mean patient age was 76.4 years (range, 51 to 88 years), and the mean IOP was 20.8 ±5 mm Hg (range, 13 to 36 mm Hg). Patients took a mean of 2.9 medications.

Fourteen patients underwent phacoemulsification with implantation of two bypasses, and 11 patients underwent phacoemulsification with implantation of three bypasses. Patients had either primary open-angle glaucoma (n = 16) or pseudoexfoliative glaucoma (n = 9) and had not undergone a previous glaucoma incisional surgery.

Patients were followed for a minimum of 6 months postoperatively; 17 of the patients were followed for up to 1 year. Mean follow-up was 9.7 ± 2.9 months. Patients continued to take their IOP medications after surgery, with a step-wise reduction in medications during the first three postoperative months.