Glaucoma Drainage Device (Tube Shunt) Surgery
A durable, reliable surgical option for complex or previously-operated glaucoma, using a small silicone tube to redirect fluid to a drainage plate on the surface of the eye.
What Is a Glaucoma Drainage Device?
A glaucoma drainage device (tube shunt) is a small silicone tube connected to a drainage plate, surgically implanted to redirect fluid from inside the eye to a reservoir on the surface of the eye, further back than a trabeculectomy bleb, under the conjunctiva. Over several weeks, the body forms a thin fibrous capsule around the plate that regulates how quickly fluid drains, controlling eye pressure long-term.
Ahmed Valve vs. Baerveldt Implant
The Ahmed valve incorporates a mechanical flow-restricting valve that begins to function immediately, which reduces (though doesn't eliminate) the risk of the eye pressure dropping too low right after surgery. The Baerveldt implant has no internal valve; instead, the tube is temporarily tied off or restricted with an internal suture at the time of surgery, and this restriction is gradually released over the following weeks as the surrounding capsule matures enough to regulate flow on its own, sometimes requiring a brief staged procedure to fully open the tube.
Indications
- ✓Glaucoma that hasn't been adequately controlled by drops, laser, MIGS, or a prior trabeculectomy
- ✓Significant conjunctival scarring from previous eye surgery that would compromise a trabeculectomy's chance of success
- ✓Neovascular glaucoma, where the abnormal blood vessels increase the risk of bleeding and scarring with trabeculectomy
- ✓Uveitic glaucoma, given the higher risk of bleb scarring in chronically inflamed eyes
- ✓Certain pediatric and other complex secondary glaucomas
Risks & Complications
- ✓Tube exposure or erosion through the conjunctiva over time, occasionally requiring a patch graft or revision
- ✓Corneal decompensation if the tube contacts or rubs against the inner corneal surface
- ✓Double vision (diplopia), particularly with the larger Baerveldt plate, related to its effect on the adjacent eye muscle
- ✓A temporary phase of low or high eye pressure during the early post-operative period, especially before a Baerveldt implant's tube is fully opened
- ✓Infection, bleeding, or choroidal effusion, as with any intraocular surgery
How It Compares to Trabeculectomy
The Tube Versus Trabeculectomy (TVT) study and the newer Primary Tube Versus Trabeculectomy (PTVT) study directly compared these two surgical approaches in randomized trials.1,2 Both procedures can achieve excellent long-term pressure control; tube shunts have shown particular advantages in eyes with prior failed filtering surgery or significant scarring, which is reflected in how we individualize this choice for each patient. See our Trabeculectomy page for the other side of this comparison.
References
- Gedde SJ, Schiffman JC, Feuer WJ, et al. Treatment Outcomes in the Tube Versus Trabeculectomy (TVT) Study after Five Years of Follow-up. Am J Ophthalmol. 2012;153(5):789-803.
- Gedde SJ, Feuer WJ, Lim KS, et al. Treatment Outcomes in the Primary Tube Versus Trabeculectomy (PTVT) Study after 1 Year of Follow-up. Ophthalmology. 2018;125(5):650-663.
Frequently Asked Questions
What's the difference between Ahmed and Baerveldt implants?
The Ahmed valve has a built-in flow-restricting mechanism that reduces the risk of the eye pressure dropping too low in the early post-operative period. The Baerveldt implant has no such valve, so the tube is temporarily occluded (tied off or restricted) at the time of surgery and gradually opened over several weeks, once a controlling scar capsule has formed around the plate.
Why would I need a tube shunt instead of trabeculectomy?
Tube shunts are often preferred when a prior trabeculectomy has failed, when there's significant conjunctival scarring from previous surgery, or in certain glaucoma types (such as neovascular or uveitic glaucoma) where trabeculectomy has a higher failure rate.
Will I be able to feel the implant?
The plate is positioned toward the back of the eye under the conjunctiva and eyelid, so it isn't visible in the mirror, though some patients are aware of a firmness in that area, especially with eye movement or when rubbing the eye.
How long does the device last?
Tube shunts are designed to function long-term (often for many years to a lifetime), though as with any glaucoma surgery, additional treatment can still be needed over time as glaucoma is a chronic, progressive condition.
See a glaucoma specialist. Dr. Robert Gunzenhauser is Harvard-educated and UCLA fellowship-trained in glaucoma, providing expert diagnosis and treatment for Tube Shunt (Ahmed & Baerveldt) Surgery at Inland Glaucoma Center in Upland, CA.