New Developments in Glaucoma Treatment: Micro-Stents

photograph of retina showing glaucomatous cupping of the optic disc

Year One results from the HYDRUS I clinical trial of the Hydrus Microstent, which has the potential for long-term reduction of intraocular [i.e., within the eye] pressure in patients with open-angle glaucoma, were presented at the 2012 American Academy of Ophthalmology Annual Meeting, held from November 10-13 in Chicago, Illinois.

Ivantis, Inc., an Irvine, California-based company that is dedicated to the development of new and innovative solutions for controlling intraocular pressure in glaucoma, is the developer of the Hydrus Microstent and funder of the current study.

About the Hydrus Microstent

From the Ivantis, Inc. website:

The Hydrus Microstent is designed to relieve the high intraocular pressure (IOP) that is common in patients with primary open-angle glaucoma (POAG). In POAG, eye pressure increases because the eye’s fluid channels become blocked. The tiny Hydrus Microstent “scaffold” is designed to be inserted into the primary fluid canal … of the eye and open the channel to allow blocked fluid to flow more freely, thus reducing high IOP. The device, about the size of an eyelash, is made from nitinol, a highly elastic … alloy used in many implantable medical devices.

You can read more about the Hydrus Microstent device, including its design, mechanism, safety, and effectiveness, at the Ivantis, Inc. website, where you can also view a photo of the Hydrus Microstent’s relative size, as compared with a U.S. quarter.

About Open-Angle Glaucoma

Glaucoma is a group of eye diseases that damage the optic nerve and is one of the leading causes of vision loss and blindness. Open-angle glaucoma is the most common form of glaucoma.

The eye continuously produces a fluid, called the aqueous (or aqueous humor), that must drain from the eye in order to maintain healthy eye pressure. Aqueous humor is a clear, watery fluid that flows continuously into, and out of, the anterior chamber of the eye, which is the fluid-filled space between the iris and the cornea. It is the aqueous that helps to bring nutrients to the various parts of the eye.

Aqueous fluid drains from the anterior chamber through a filtering meshwork of spongy tissue along the outer edge of the iris (the trabecular meshwork), where the iris and cornea meet, and into a series of tubes, called Schlemm’s canal, that drain the fluid out of the eye. Problems with the flow of aqueous fluid can lead to elevated pressure within the eye.

In primary open-angle glaucoma, the filtering meshwork may become blocked or may drain too slowly. If the aqueous fluid cannot flow out of the eye, or flow out quickly enough, pressure builds inside the eye and can rise to levels that may damage the optic nerve, resulting in vision loss.

Note: Most eye care professionals define the range of normal intraocular pressure as between 10 and 21 mm Hg [i.e., millimeters of mercury, which is a pressure measurement].

The Study Results Thus Far

Thomas W. Samuelson, MD, adjunct associate professor of ophthalmology at the University of Minnesota and medical monitor of the HYDRUS I clinical trial, summarized the Year One clinical trial results:

In this particular study of 69 patients [with] mild to moderate open-angle glaucoma, IOP was reduced to acceptable levels in 100 percent of participants after they received minimally invasive [micro]stent implant surgery.

In 40 patients, the stent was placed during cataract surgery, a procedure that also reduces IOP.

Twenty-nine patients had the Hydrus stent placed without cataract surgery to assess whether the stent would be effective on its own. No significant complications occurred in either patient group.

At the six-month follow-up, 85 percent of combined surgery and 70 percent of stent-only patients no longer needed eye drop medications to control their IOP. Reductions in IOP were consistent among all patients and remained stable at the one year follow up.

Clinical Trials and the Hydrus Microstent

Most clinical trials are designated as Phase I, II, or III, based on the questions the study is seeking to answer:

  • In Phase I clinical trials, researchers test a new drug or treatment in a small group of people (20-80) for the first time to evaluate its safety, determine a safe and effective dosage range, and identify possible side effects.
  • In Phase II clinical trials, the study drug or treatment is given to a larger group of people (100-300) to determine if it is effective and to further evaluate its safety.
  • In Phase III studies, the study drug or treatment is given to even larger groups of people (1,000-3,000) to confirm its effectiveness, monitor side effects, compare it to commonly used treatments, and collect information that will allow the drug or treatment to be used safely.
  • In Phase IV studies, after the Food and Drug Administration (FDA) has approved the drug, continuing studies will determine additional information, such as the drug’s risks, side effects, benefits, and optimal use.

At present, Ivantis, Inc is enrolling patients for a large Phase III clinical trial, called the HYDRUS IV, which will compare patients undergoing cataract surgery with and without the Hydrus Microstent. The Ivantis website provides helpful information about the clinical trial, including criteria for enrollment and a list of participating centers/sites.

Additional Information – and Cautions

A number of similar microstents, including the MIDI Arrow, Aquecentesis, and Transcend are now in development or clinical trials. The iStent was recently approved by the U.S. Food and Drug Administration for use in conjunction with cataract surgery.

Please note: Despite encouraging initial results, it will be several years before the long-term safety and effectiveness of microstents can be confirmed. Also, because this study was presented at a medical conference, the results should be viewed as preliminary until they are published in a peer-reviewed journal.

VisionAware will provide updates on microstent research as they become available.