iStent

The eye constantly makes a clear fluid called aqueous humor. The fluid bathes the inside of the front of the eye and then drains out through the trabecular meshwork into Schlemm's canal, and from there into the small veins of the eye. In open-angle glaucoma, the trabecular meshwork is partly blocked. Fluid backs up, eye pressure rises, and the optic nerve is slowly damaged.

iStent is a tiny snorkel-shaped titanium tube. The original device is the smallest medical implant ever placed in the human body. The newer iStent inject and iStent inject W use two stents shaped like miniature studs.

During surgery, the eye surgeon uses a small applicator to push the stent through the trabecular meshwork. The stent then sits with one end in the anterior chamber (where the fluid is) and the other end in Schlemm's canal (the outflow channel). It creates a tiny direct path for the fluid to drain, bypassing the blocked meshwork.

iStent does not change how the eye looks. The stent is much too small to see without a microscope, and it does not change the color of the iris or the appearance of the pupil.

iStent is approved for:

• Adults with mild to moderate primary open-angle glaucoma.
• Patients already on glaucoma medications who are having cataract surgery.
• Standalone use (without cataract surgery) is approved for iStent inject W in adults with mild to moderate primary open-angle glaucoma.

The U.S. labeling and indications for use are spelled out in the FDA PMA approval order for the device ².

iStent is generally NOT used for:

• Advanced or severe glaucoma — the pressure reduction is usually not enough.
• Angle-closure glaucoma, neovascular glaucoma, uveitic glaucoma, or other secondary glaucoma where the angle is scarred or blocked by other structures.
• Patients who need very low eye pressure targets — trabeculectomy or a tube shunt usually achieves more.

iStent is one of several MIGS options. A JAMA Ophthalmology overview of Cochrane systematic reviews on minimally invasive glaucoma surgical techniques summarizes the evidence base for iStent and other devices ⁶. A network meta-analysis comparing the Hydrus and iStent microinvasive glaucoma surgery implants found similar safety and effectiveness in combined cataract surgery ⁷.

Most iStent procedures are done at the same time as cataract surgery. The combined operation takes about 20-40 minutes.

Before surgery:

• You meet your cataract surgeon and a glaucoma specialist (sometimes the same surgeon does both). They check your eye pressure, the angle of the eye, your optic nerve, and your visual field.
• You stop or continue glaucoma drops as instructed.
• The eye is dilated on surgery day.

During surgery:

• You stay awake but get a mild sedative through an IV.
• The cataract is removed first through a small incision (phacoemulsification).
• A new artificial lens is placed inside the lens capsule.
• Then the surgeon turns the head slightly, places a small lens called a gonioprism on the eye to see the drainage angle, and uses an applicator to insert the iStent through the trabecular meshwork.
• The cuts seal themselves and you go home with a clear shield.

After surgery:

• Recovery is very similar to standard cataract surgery — antibiotic and anti-inflammatory eye drops for 3-4 weeks.
• Your eye doctor checks the eye pressure carefully in the first weeks and adjusts glaucoma drops up or down depending on the response.
• If iStent is done as a standalone procedure (without cataract surgery), recovery is even faster, typically 1-2 days back to normal activities.

iStent is one of the safest glaucoma surgeries. Most side effects are short-lived and similar to standard cataract surgery.

• Bleeding inside the eye (hyphema). Tiny amounts of blood from the trabecular meshwork are common during the procedure. Usually clear within days.
• Brief eye pressure spike or dip. Pressure can be temporarily high or low in the first days; usually managed with drops.
• Stent malposition or obstruction. Rare. The stent can be in the wrong spot or get blocked. May need a small office procedure to reposition or replace.
• Need for additional glaucoma surgery. Some patients still need a second procedure (laser, trabeculectomy, or tube shunt) over time, especially if glaucoma worsens.
• Blurry vision and the usual cataract surgery risks when iStent is combined with phaco — infection, swelling, retinal problems — but these are very rare.

Evidence comparing iStent against other MIGS options like Kahook Dual Blade goniotomy combined with phacoemulsification shows similar safety and similar pressure-lowering effect ⁸. Recent systematic reviews evaluate iStent micro-bypass against Kahook Dual Blade goniotomy with phacoemulsification in open-angle glaucoma to help guide selection ⁹. Use of iStent as a standalone operation in patients with open-angle glaucoma has also been reviewed and shows modest but durable pressure reductions ¹⁰.

What iStent costs in the U.S.:

• The total cost is usually built into the cost of the cataract surgery. The surgeon's fee, the surgery center fee, the stent device, and the cataract part of the operation are typically billed together.
• The iStent device alone has a wholesale list price of around $1,000-$1,500 in the U.S., but patients almost never see this number on a bill.

What insurance usually covers:

• Medicare and most U.S. health insurance plans cover iStent when it is placed at the time of cataract surgery in eligible patients with mild to moderate open-angle glaucoma already on glaucoma drops. The 2012 FDA approval (PMA P080030) set the original combined indication ².
• Standalone iStent inject W (without cataract surgery) is also covered for the labeled indication, though more often as a separate billed procedure.
• You typically pay your normal deductible, copay, and coinsurance — not an extra cash fee for the stent itself.

Cost-effectiveness:

• A Canadian cost-utility analysis of two trabecular microbypass stents at the time of cataract surgery in patients with mild to moderate open-angle glaucoma found that iStent inject was cost-effective compared with cataract surgery alone, mainly through reduced medication costs and fewer follow-up visits over time ¹¹.