On June 25, 2012, the U.S. Food and Drug Administration (FDA) announced that it had approved the iStent Trabecular Micro-Bypass Stent System. This is the first stent device approved for use in combination with cataract surgery to reduce intraocular [i.e., within the eye] pressure in adult patients with mild or moderate open-angle glaucoma and a cataract who are currently being treated with medication to reduce intraocular pressure. The iStent was developed by the Glaukos Corporation in Laguna Hills, California. The iStent device has already been approved for use in Europe.
About the Glaukos Corporation
The Glaukos Corporation was founded in 2001. It is an ophthalmic medical device company that is focused on the management of open-angle glaucoma through the development of micro-bypass technologies for micro-invasive glaucoma surgery (MIGS). The goal of these technologies is to help patients achieve and maintain intraocular pressure within normal limits and reduce the challenges and risks of glaucoma management.
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]. Intraocular pressure greater than 21 mm Hg is considered higher than normal. You can read more about intraocular pressure at the emedicine website.
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 inside 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.
How the iStent Device Works
The iStent is a very small titanium tube, approximately one millimeter in length. It is surgically placed into the eye through an incision in the cornea and inserted through the filtering tissue meshwork. This creates an opening between the eye’s anterior chamber and Schlemm’s canal that bypasses the damaged drainage system and directs the aqueous fluid into deeper tissues, potentially decreasing intraocular pressure.
You can read more about the iStent device, including its design, mechanism, safety, and effectiveness, at the Glaukos website, where you can also view photos of the iStent design and relative size, as compared with a U.S. penny.
The FDA Approval Process
From the FDA announcement:
The FDA reviewed effectiveness data from a study total of 240 eyes for 239 participants (one participant had both eyes evaluated). The FDA also reviewed the safety data for these and an additional 50 participants. At one year following the procedure, 68 percent of participants with the iStent had the study target pressure of 21 millimeters of mercury or lower without the use of eye pressure-lowering medication, compared to 50 percent of participants who underwent cataract surgery alone.
“The iStent is a new option that may be considered in the treatment of open-angle glaucoma in patients needing cataract extraction,” said Christy Foreman, director of the Office of Device Evaluation at FDA’s Center for Devices and Radiological Health. “This option may be considered earlier in the disease process than some other types of surgical glaucoma treatments.”
About Glaucoma and Cataracts That Occur Together
On the Glaucoma Research Foundation website, Andrew G. Iwach, MD, Assistant Clinical Professor of Ophthalmology at the University of California, San Francisco explains the treatment issues to consider when a patient has coexisting cataracts and glaucoma:
When treatment for a cataract is warranted, it is surgically removed and an artificial lens is put in its place. Glaucoma, however, damages the optic nerve, the critical structure that transmits the visual signal from the eye to the brain. Unfortunately, in contrast to cataracts, we are not yet able to repair or replace the optic nerve. This important difference affects the management of these two diseases when they co-exist in the same eye.
The ophthalmologist tailors the specific treatment plan for the individual eye to maximize the benefits and minimize the risk to the eye. The ophthalmologist balances many factors that affect the decision as to when and how aggressively the glaucoma and cataract should be treated, including whether the two diseases should be treated at the same time or separately. There are a number of options available to glaucoma patients with cataracts, and each situation must be assessed individually.
Other Stents in Development
Glaukos is planning to develop a full portfolio of micro-bypass stents, all targeting glaucoma. In addition, the Hydrus Microstent and the AqueSys stent are also in clinical trials. VisionAware will report on these stent developments as information becomes available.