Aqueous Shunt for Glaucoma
Aqueous shunt insertion is an incisional procedure for the treatment of eye pressure (intraocular pressure) caused by glaucoma. The goal of the procedure is to relieve intraocular pressure and prevent further vision loss caused by damage to the optic nerve.
During the procedure, your surgeon will insert a small, flexible tube through an opening made in the wall of the eye where the cornea (the clear part of your eye) meets the sclera (the white part of your eye). The aqueous shunt will then act as a drain to move the eye’s fluid (aqueous humor) to one or two reservoirs attached to the sclera near the equator of the eye. Aqueous shunt insertion often leads to a reduced need for medical treatment of your glaucoma. Some tubes have valves that allow immediate outflow of aqueous humor from the eye thus lowering the intraocular pressure immediately. Non-valved tubes require more time to establish outflow of fluid but tend to last longer and require fewer drops after surgery.
Who Is a Good Candidate for Aqueous Shunt Insertion?
Aqueous shunt insertion can be used to treat several types of glaucoma when a trabeculectomy cannot be performed or for those who have had several unsuccessful trabeculectomies in the past. Types of glaucoma that commonly require treatment via aqueous shunt include congenital glaucoma, neovascular glaucoma, and glaucoma caused by an eye injury.
It’s important to note that glaucoma surgery, including aqueous shunt insertion, cannot cure glaucoma or undo vision loss, but it can help lower intraocular pressure and prevent further loss of vision. Your surgeon will determine if you are a good candidate for aqueous shunt insertion based on your unique situation.
Types of Aqueous Shunts
There are three main types of aqueous shunts that may be used to treat your glaucoma. These include:
- Ahmed Glaucoma Valve
- Baerveldt Glaucoma Implant
- Molteno Implant
Aqueous shunts are comprised of a small silicone tube attached to a plate. Aqueous humor is drained from the eye via the tube and deposited into the plate, which sits on the sclera near the equator of the eye. All three types of shunts perform essentially the same function, but provide different advantages for regulating eye pressure following surgery.
Before the Procedure
Blood tests and an electrocardiogram may be ordered prior to the procedure. Your surgeon will usually recommend that you stop taking blood thinners (especially Coumadin), products containing aspirin, and many arthritis medications usually seven to 10 days before surgery (after receiving approval from your personal physician).
You may not eat or drink in the six hours leading up to your surgery. You may continue to use your prescribed glaucoma eye drops and take other normal medications (with water only), unless otherwise instructed by your surgeon. Those who have diabetes and/or use insulin will receive special instruction from their surgeon prior to surgery.
During the Procedure
The procedure is typically performed under local anesthesia with careful monitoring from our staff. You will also be sedated in the pre-operative area or in the operating room.
You will be monitored to ensure that you remain medically stable and comfortable. You should not experience much pain, although you may feel some pressure around the eye being treated.
A Molteno or Baerveldt implant may be used to prevent excessive drainage of fluid in the first four to six weeks after surgery. When these implants are used, your surgeon will purposefully obstruct the tube with a dissolvable stitch during the procedure. The Ahmed implant, on the other hand, has a valve between the tube and the reservoir to keep eye pressure from going too low.
To prevent the tube from eroding through the conjunctiva (the membrane that covers your eye), your surgeon will cover it with a patch fashioned from highly processed human pericardial, scleral, or corneal tissue. This patch, the underlying tube, and the reservoir(s) are then covered with the conjunctiva.
Following the Procedure
You may have a patch placed over the treated eye. When your surgeon deems you are stable in the recovery area, you will be discharged to be driven home by a friend or family member. A follow-up appointment at DMEI will be scheduled for the next morning, at which time your patch will be removed and the eye examined.
When aqueous humor flows through the shunt, it forms a bubble of fluid over the reservoir(s) and then is absorbed into the surrounding tissues and bloodstream.
You will be prescribed medications to reduce inflammation and prevent infection in the eye. These will be tapered over several weeks to months as the inflammation in the eye subsides and the risk for infection decreases.
To protect your eye after surgery, you should wear your glasses or sunglasses during the day and a plastic shield at night. Your doctor will also give you instructions regarding activity restrictions. In general, you should avoid heavy lifting, strenuous activity, bending or stooping below the waist, or hard nose blowing during the first few weeks following surgery or until the eye pressure stabilizes.
Are There Risks Associated with Aqueous Shunts?
Possible, but rare, complications can include severe bleeding either during or after the surgery, severe infection, or permanent worsening or loss of vision. You may also experience drooping of the eyelid, decreased vision from progression of a pre-existing cataract or swelling in the back of the eye, or excessive scarring over the reservoir(s) with a rise in eye pressure.
Sometimes, your eye pressure can remain very low, the shunt device may become exposed, or the portion of the shunt tube inside the eye may become malpositioned as the eye heals. Rarely, double vision may develop that cannot be corrected with glasses. These problems may require revision or removal of the shunt device.
It is typical for the vision to be initially blurred after surgery. Depending on how your eye responds to the surgery, it may take a few or several weeks for the vision to recover.
Your intraocular pressure immediately after the surgery may be low. However, the pressure usually begins to rise one or two weeks later until the obstructing stitch placed around the tube dissolves in four to six weeks.
In some cases, eye pressure is initially high and then drops when the stitch degrades. During this high-pressure phase after the surgery, you may need to continue or resume using prescribed glaucoma medications. These may then be decreased or discontinued when the shunt begins to drain the eye’s fluid. Your doctor may also choose to cut the stitch with a laser before it dissolves.