Your doctor has recommended that you undergo an incisional glaucoma procedure known as aqueous shunt surgery for your eye. When someone has glaucoma that cannot be controlled with medications or laser surgery, incisional surgery becomes necessary. In most instances, this is achieved by a standard procedure known as a trabeculectomy, in which a small controlled opening is made in the wall of the eye to allow increased drainage of the eye’s inner fluid (called the aqueous). However, in some eyes, the usual trabeculectomy procedure cannot be performed because of extensive scarring (usually due to previous surgeries on the eye) of the eye’s covering membrane (called the conjunctiva). In other cases, the chance that the standard procedure will control the eye pressure is very low because the eye has a very complex type of glaucoma (such as that due to trauma, inflammation, or blood vessel growth) or because the eye has already had one or more unsuccessful trabeculectomies. For one or more of these reasons, it is advised that an aqueous shunt device be placed in your eye. There are different types of shunts, including the Molteno, Baerveldt, and Ahmed implants.
A small, flexible tube is inserted into your eye through an opening made in the wall of the eye, usually where the cornea (the clear window portion of the eye) meets the sclera (the white part of the eye). Sometimes the tube is placed farther back through the sclera. This tube then acts as a drain to shunt the eye’s fluid, the aqueous, to one or two reservoirs attached to the sclera on the top of the eye. To avoid the complication of excessive drainage of fluid, which can occur in the first one to two weeks postoperatively, the tube in Molteno and Baerveldt implant surgery is purposefully occluded with a dissolvable stitch at the time of the surgery. The Ahmed implant has a valve between the tube and the reservoir to keep the pressure from going too low. To prevent the tube from eroding through the conjunctiva (the membrane that covers the eye), it is covered with a patch fashioned from highly processed human pericardial tissue. This patch, the underlying tube, and the reservoir(s) are then covered with the conjunctiva. In four to six weeks, after the danger of excessive drainage has passed, the occluding stitch degrades, and the fluid begins to flow through the shunt. This shunted fluid forms a bubble of fluid over the reservoir(s) and then is absorbed into the tissues and blood stream. The purpose of this extra drainage pathway is to allow the eye pressure to drop, thereby achieving better control of your glaucoma and allowing the possibility of decreased reliance on glaucoma medications.
Before the surgery
You will receive instructions regarding the surgery from your doctor and the staff. Sometimes, some blood tests and an electrocardiogram will be ordered before surgery. If you take aspirin, aspirin-containing products, or arthritis medications, it is usually best to stop these medications seven to ten days before surgery if it is acceptable to your regular personal physician. If you are taking Coumadin or other blood thinners, it is particularly important that you make your doctor and the staff aware of this fact.
In preparation for your surgery, you may eat or drink until 6 hours before surgery. If your surgery is scheduled in the afternoon, we would suggest that any breakfast on the morning of surgery include only "clear" liquids. For your own comfort during surgery, please avoid any heavy foods. On the day of surgery, you may use your eye drops as you normally do. You also should take your other normal medications as usual with water on the morning of surgery. If you have diabetes, and particularly if you use insulin, you should receive special instructions from your doctor and the staff regarding your diet and the use of insulin on the day of surgery.
At the surgery center or hospital
When you arrive, you will be asked some questions at the admitting desk and also by the staff in the pre-surgical area, who will help you get ready for surgery. Most adult glaucoma surgery is performed under local anesthesia with careful monitoring by our anesthesia staff. You will be sedated in the pre-operative area or in the operating room. In the operating room itself, you will monitored throughout the procedure to make sure that you are medically stable and comfortable. During the procedure, you should not experience very much pain. You may notice some pressure sensations around the eye. When the surgery is completed, you may or may not have a patch over the eye depending on the type of anesthesia that was used.
Benefits and risks of surgery
The benefit of incisional glaucoma surgery is improved control of the glaucoma, often with a reduced or eliminated need for medical treatment. Glaucoma surgery does not "cure " glaucoma. Like any surgical procedure, complications can occur. The most serious complications include severe bleeding either during or after the surgery, severe infection, or permanent worsening or loss of vision. Fortunately, these are rare. Other possible problems associated with tube shunt surgery include 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 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.
After the surgery
Once you are felt to be stable in the recovery area, you will be discharged and seen the next morning at the McGee Eye Institute. On the morning after surgery, the patch will be removed from the eye, and the eye will be carefully examined. 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. Sometimes the pressure in the eye immediately after the surgery is low. One or two weeks later, however, the pressure usually begins to rise until the occluding stitch placed around the tube dissolves in four to six weeks. In some instances, the 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 glaucoma medications. These may then be decreased or discontinued when the shunt begins to drain the eye’s fluid. Sometimes, the doctor may choose to cut the stitch with a laser before it dissolves. You also will be on some medications to reduce inflammation and prevent infection in the eye. These will be tapered over several weeks as the inflammation in the eye subsides and the risk for infection decreases.
To protect the eye after surgery, you should wear your glasses or sunglasses during the day and the plastic shield provided to you over the eye while sleeping or napping. This avoids any inadvertent bumping or rubbing of the eye. Your doctor also will give you instructions regarding activity restrictions after the surgery. In general, you should avoid any heavy lifting, strenuous exercise, bending or stooping below the waist, or hard nose blowing during the first few postoperative weeks.
Our goal is to provide you with the best possible surgical care. We hope that this information is helpful. If you should have any additional questions or concerns regarding your surgery, please feel free to speak with your doctor or a member of the staff.