New glaucoma devices take different approaches to IOP lowering

Devices both FDA approved and awaiting approval in clinical trials hold promise for faciliating aqueous outflow without a bleb.

Issue: February 1, 2006

ByErin L. Boyle

A variety of new stents and shunts for use in refractory glaucoma are now or may soon be in the hands of glaucoma surgeons. These devices, designed to facilitate outflow of aqueous from the anterior chamber in diverse ways, may allow IOP-lowering surgery without a postoperative bleb, potentially increasing the safety and efficacy of glaucoma surgery.

Only one of these devices has Food and Drug Administration approval, but a number of them have been approved for use in Europe. The devices profiled in this article are the ExPress miniature glaucoma shunt from Optonol, the Minicatheter from iScience, the iStent from Glaukos, the DeepLight Gold MicroShunt from Solx and the EyePass from GMP.

Optonol ExPress

The ExPress Mini Glaucoma Shunt from Optonol works by bypassing the blocked trabecular meshwork, allowing aqueous humor to drain from the anterior chamber into the intrascleral and subconjunctival spaces, where it is absorbed by the blood vessels, according to information provided by the company.

The device received FDA approval in 2002 and became commercially available for sale in the United States in 2003, according to Harel A. Orbach, director of marketing for Optonol.

A study by Peter J.G. Maris, Jr., MD, and Peter A. Netland, MD, PhD, presented at the 2005 American Academy of Ophthalmology meeting, compared the ExPress with trabeculectomy in two groups of 50 eyes. The study authors found that, in eyes in which the ExPress was implanted beneath a scleral flap, IOP decreased 53.7% postoperatively. In eyes that underwent trabeculectomy, IOP was reduced 53.6%. Hypotony occurred in 6% of eyes with the implant, compared with 34% of eyes that underwent trabeculectomy.

“It appeared to us that ExPress performed equally to trabeculectomy in terms of lowering pressure adequately and reducing a patient’s dependence on drops, but there was a very significant difference regarding hypotony,” Dr. Maris said in a telephone interview with Ocular Surgery News. “There was a much higher incidence of hypotony with standard trabeculectomy, including some with choroidal detachments. That was a very big advantage for the ExPress.”

Dr. Maris said a U.S. study of the device found that, in 75 eyes of high-risk glaucoma patients, mean IOP reduction was 41.5% at 1 month; 48% at 3 months; 44.8% at 9 months; and 54.1% at 12 months. At their last follow-up visit, 25.6% of patients needed adjunctive IOP-lowering medications.

A good trabeculectomy technique is important to using the ExPress successfully, Dr. Maris said. He suggested placing the device under a scleral flap instead covering it only with conjunctiva, the technique that was first proposed. He said the device should not press against the iris and should not be placed too close to the cornea.

“You really want to find the appropriate plane when you insert it,” Dr. Maris said.

iScience Minicatheter

The Minicatheter from iScience is inserted into the canal of Schlemm in a procedure similar to viscocanalostomy, according to Richard A. Lewis, MD. The product has not yet received FDA approval. Dr. Lewis, who is taking part in clinical trials of the device, said he will present interim results of the ongoing study at a meeting in March.

“The learning curve is centered around getting comfortable identifying Schlemm’s canal,” he said.

Ronald L. Fellman, MD, who has also used the Minicatheter, said it is “promising” as a device to facilitate outflow, and the postoperative course may be safer than trabeculectomy. He said the device helps to “better define” the canal of Schlemm, providing surgeons with a clearer picture of the anatomy.

“It is a procedure that will teach us more about outflow,” he said. “It’s a major improvement in visualization.”

Glaukos iStent

The iStent, from Glaukos Corporation, is a small “spike-like” implant that is inserted across the anterior chamber and into the trabecular meshwork, according to E. Randy Craven, MD. It is designed to allow aqueous to enter the canal of Schlemm to help lower IOP, Dr. Craven said. The device is currently in an investigational stage and not FDA approved.

“Moving from making filtering blebs to finding some other alternate way for aqueous to get out of the eye is exciting and promising because it has lower risks associated with it. It’s safer for the patient and actually easier to do, if you are able to technically get it in the right place,” he said. “I think that the device holds great promise.”

He said thus far, in two patients in which he has inserted the device, the results have been promising. A woman who had previous cataract surgery had “substantially” improved IOP in the eye in which the iStent was implanted, he said.

While implantation of the device appears to be straightforward, Dr. Craven said, it requires great attention to detail and care. The device is very small, with a width of 80 µm and length of 1 mm.

“Technically, it takes some time to get used to positioning it, to get the right angle to go ahead and put it into the correct place,” he said. “It’s small enough that you really have to put the microscope on high magnification and make sure you get everything in the right place while you’re putting it into the trabecular meshwork. You have to have a very steady hand and be exactly in the right place, hopefully, when you place it.”

He said a goniolens is used to view the angle while moving the iStent across the anterior chamber. He said the surgeon should visualize the trabecular meshwork and insert the device deeply to make sure it enters Schlemm’s canal.

“That takes a little bit of practice because it’s such a fine, delicate thing to do, but I think with practice people should do it fairly easily,” Dr. Craven said.

Solx DeepLight Gold MicroShunt

The 24-karat DeepLight Gold MicroShunt from Solx is designed to lower IOP in a procedure without a bleb, according to the manufacturer. The implantable device reduces IOP by taking advantage of the natural pressure differential between the anterior chamber and the suprachoroidal space, according to information provided by Solx.

The device, which is in clinical trials for FDA approval in the United States, received European CE approval in October 2005.

The ultra-thin device is inserted into a 4-mm-wide incision that connects the anterior chamber to the suprachoroidal space in a minimally invasive procedure, according to the company.

In the clinical trial results that were submitted to the European Agency for the Evaluation of Medicinal Products, 70 eyes of patients with open-angle glaucoma that was uncontrolled despite maximum medical therapy and one surgical intervention were followed for up to 2 years after implantation of the MicroShunt. The eyes experienced a mean reduction in IOP of more than 34% compared to baseline on maximum medication, according to Solx.

“Complications and adverse events with the (DeepLight Gold MicroShunt) were low and transient in almost all cases, especially as compared to the reported complications and adverse events associated with blebs,” the company said.

The device is a flat plate implanted through a single microincision, according to the company. It has an array of micro-tubular channels that work as a bridge between the anterior chamber and suprachoroidal space, allowing outflow through the device and around it, the company said.

“The (DeepLight Gold MicroShunt) rests permanently in the suprachoroidal space and cannot be felt by the patient. It is also biocompatible, physically inert and has been shown to eliminate the formation of scar tissue,” according to company literature.

GMP EyePass

Officials from GMP, maker of the glaucoma implant EyePass, said their investigational device is currently in phase 3 trials for the treatment of patients with glaucoma. The study is taking place at up to 20 investigational sites in the United States, according to the company’s Web site. A company spokesperson declined to provide more information to Ocular Surgery News about results with the device while the clinical trial is ongoing.

Ocular Surgery News has previously reported that the EyePass consists of two flexible silastic tubes, 150 µm in diameter, which are joined in a Y configuration. The two arms of the Y are inserted into Schlemm’s canal, and the stem of the Y is inserted into the anterior chamber, according to Garry P. Condon, MD, speaking at the American Society of Cataract and Refractive Surgery meeting in 2004. Dr. Condon reported at that meeting that a phase 1 safety trial revealed no significant safety issues with the device. He said at the time that a phase 2 study of the efficacy and safety of the device had begun.

For Your Information:

E. Randy Craven, MD, can be reached at Glaucoma Consultants of Colorado, 26 W. Dry Creek Circle, #225, Littleton, CO 80120; 303-797-1900; fax: 303-347-1341; e-mail: ercraven@glaucdocs.com.

Ronald L. Fellman, MD, can be reached at Glaucoma Associates of Texas, 7150 Greenville Ave., Suite 300, Dallas, Texas, 75231-5185; 214-360-0000.
Richard A. Lewis, MD, can be reached at 1515 River Park Drive, Sacramento, CA 95815; 916-649-1515; fax: 916-649-1516; e-mail: rlewiseyemd@yahoo.com.

Peter J. G. Maris Jr., MD, can be reached at11 Surrey Lane, Old Westbury, NY, 11568; e-mail: pmaris@utmem.edu.

Peter A. Netland, MD, PhD, can be reached at the University of Tennessee Health Science Center, 930 Madison Ave., Suite 100, Memphis, TN, 38163; 901-448-5883.

The iStent is manufactured by Glaukos Corp., 26061 Merit Circle, Suite 101, Laguna Hills, CA 92653; 949-367-9600; e-mail: contact@glaukos.com; Web site: www.glaukos.com.
The Minicatheter is manufactured by iScience Surgical Inc., 3696 Haven Avenue, Suite A, Redwood City, CA 94063; 650-421-2700.
The EyePass glaucoma implant is manufactured by GMP Companies Inc., One East Broward Boulevard, Suite 1701, Fort Lauderdale, FL 33301; 954-745-3510 or 888-723-3310; fax: 954-745-3511; e-mail: gmp.info@gmpcompanies.com; Web site: gmpcompanies.com.
The DeepLight Gold MicroShunt is manufactured by Solx Inc, 8 Saint Mary’s St., Suite 629, Boston, MA 02215; 800-939-7659 or 978-717-9482; e-mail: info@solx.com; Web site: www.solx.com.
The Ex-Press Mini Glaucoma Shunt is manufactured by Optonol Ltd., P.O. Box 2367, Kansas City, KS 66110-0367; 877-707-3937; fax: 816-241-8347; Web site: www.optonol.com.

Erin L. Boyle is an OSN Staff Writer who covers all aspects of ophthalmology.