iStent — Trabecular Micro-Bypass
The iStent is a tiny titanium implant — among the smallest medical devices placed in the human body — that reopens the eye's natural drainage pathway to lower pressure with an outstanding safety profile.
What Is the iStent?
The iStent is a trabecular micro-bypass stent — a microscopic titanium implant designed to restore the eye's natural drainage. The current generation, the iStent inject W, places two tiny stents during a single procedure. It belongs to the family of minimally invasive glaucoma surgery (MIGS) and is one of the most widely performed angle-based glaucoma procedures in the world.
What Happens Anatomically During the Surgery
In open-angle glaucoma, fluid (aqueous humor) is produced normally inside the eye but drains too slowly. The great majority of that drainage resistance sits at one specific location: the trabecular meshwork, the sieve-like tissue at the drainage angle, and its innermost wall against Schlemm's canal. Fluid that gets past the meshwork into Schlemm's canal is then carried away by a network of collector channels into the bloodstream.
During surgery, the eye is viewed through a gonioscopy lens to bring the drainage angle into direct view. Through the same micro-incision used for cataract surgery, the surgeon passes a tiny injector across the front of the eye and implants the stents directly through the trabecular meshwork so that each one bridges from the anterior chamber into Schlemm's canal. The stents are placed a couple of clock-hours apart to access different sets of collector channels.
The result is a permanent, direct bypass around the most resistant part of the meshwork: aqueous now flows straight into Schlemm's canal and out through the collector channels, lowering eye pressure while using the eye's own downstream plumbing.
Which Types of Glaucoma It Helps
The iStent is best suited to mild-to-moderate primary open-angle glaucoma, the most common form of the disease, and works best when the downstream drainage (Schlemm's canal and collector channels) is still healthy. In the U.S. it is used together with cataract surgery. It can also be appropriate for related open-angle conditions such as pseudoexfoliation glaucoma and pigment dispersion glaucoma. It is not a treatment for angle-closure glaucoma with a physically blocked angle, nor is it intended for advanced or neovascular glaucoma, where a larger pressure reduction is usually required.
Benefits
The iStent's appeal is its combination of effectiveness and exceptional safety:
- ✓Meaningful, reliable reduction in eye pressure and, for many patients, fewer glaucoma drops
- ✓Performed through the existing cataract incision — only a few added minutes and minimal added risk
- ✓Works within the eye's natural drainage system, so it does not create a bleb and does not disturb the conjunctiva
- ✓Preserves all future options — because the conjunctiva is untouched, trabeculectomy or tube shunt surgery remain fully available later if ever needed
- ✓Rapid visual recovery, essentially the same as cataract surgery alone
Risks & Considerations
The iStent has one of the best safety profiles of any glaucoma procedure, but no surgery is without risk. Possible issues include a small amount of bleeding in the eye (hyphema) from the drainage-angle blood vessels, a temporary rise in eye pressure in the early postoperative period, stent malposition or blockage that can occasionally require repositioning, and the possibility that the pressure reduction is not enough on its own, so that drops or an additional procedure are still needed. Because its effect is intentionally modest, the iStent is not the right choice when a very low target pressure is required.
A closely related device, the Hydrus Microstent, is a small scaffold that props open a larger, roughly three-clock-hour span of Schlemm's canal rather than creating discrete bypass points. It works on the same principle and is chosen based on each eye's anatomy and the surgeon's judgment.
The iStent is one of several MIGS options. For an overview and how it compares with canaloplasty, goniotomy, and the XEN gel stent, see our MIGS Surgery page. For more advanced glaucoma, see our Trabeculectomy and Tube Shunt Surgery pages.
Frequently Asked Questions
What is the iStent?
The iStent (currently the iStent inject W, made by Glaukos) is a trabecular micro-bypass device: one or two microscopic titanium stents are placed through the trabecular meshwork into Schlemm's canal to create a direct channel for fluid to drain, lowering eye pressure.
Is the iStent done with cataract surgery?
In the United States the iStent is FDA-approved for use in combination with cataract surgery in adults with mild-to-moderate open-angle glaucoma. It is placed through the same tiny incision used to remove the cataract, adding only a few minutes to the procedure.
Will the iStent get rid of my eye drops?
Many patients reduce their drop burden after an iStent, and some come off drops entirely, but this is not guaranteed. The iStent produces a modest, reliable pressure reduction; your specialist will set realistic expectations based on your glaucoma severity.
Is the iStent safe?
Yes. Because it works within the eye's own drainage system and does not create a bleb, the iStent has an excellent safety profile, very close to that of cataract surgery alone, and it preserves the option of more advanced surgery later if ever needed.
See a glaucoma specialist. Dr. Robert Gunzenhauser is Harvard-educated and UCLA fellowship-trained in glaucoma, providing expert diagnosis and treatment for iStent (Trabecular Micro-Bypass) at Inland Glaucoma Center in Upland, CA.