Glaucoma Drainage Implant Complications
Chat Highlights
April 7, 2010

On Wednesday, April 7, 2010, Dr. Michael Pro, a glaucoma specialist at Wills, and the glaucoma chat group discussed "Glaucoma Drainage Implant Complications".

Moderator: Welcome back Dr. Pro. Our topic this evening is Glaucoma Drainage Implant Complications.
What is a shunt and why is it used?

Dr. Pro: A shunt or tube shunt is a device used to lower the pressure. It is used in glaucoma surgery often when a trabeculectomy has failed. But the use of these devices seems to be increasing, and is also sometimes used as a primary glaucoma surgery. Basically a shunt comprises a small silicone tube attached to a plate made of silicone or other bio-compatible material.

P: That is interesting. So sometimes a shunt is used even before a trabeculectomy or laser surgery.

Dr. Pro: Yes, especially in patients who have specific types of glaucoma, like neovascular or inflammatory. But some glaucoma specialists will even use them in patients with typical primary open angle glaucoma (POAG)

P: Do any of your patients with NTG have shunts or trabs? How low can the pressure go?

Dr. Pro: Well that's the difficult part. In general we find that shunts may not get the IOP as low as with a trab. But not every glaucoma study agrees with this. In fact, one of the most important recent glaucoma studies is the tube versus trab study (TVT). This was a well designed study performed at very good academic centers. That study found similar IOP reduction between the two groups at three years. The tube group needed to use more glaucoma medications to maintain the IOP, but had fewer short term complications than the trab group. The groups had similar overall success rates.

P: What do you feel are the most common complications? Would you also please describe each one?

Dr. Pro: Mostly the complications from tube shunts are not serious. Patients may experience persistent intraocular inflammation or ocular irritation. In the short term after surgery the vision can be blurry, but usually resolves. Patients may develop cataracts and require surgery.

More serious complications are rarer. Some patients may develop double vision due to a dysfunction in eye movement. This can sometimes require special prism glasses or surgery to fix. The tube may erode through the conjunctiva, which could predispose to an infection.

Persons may develop corneal problems like persistent corneal edema. This is more often a problem in patients with corneal transplants and sometimes the tube needs to be placed in the space behind the lens rather than in the anterior chamber.

P: Is shallow anterior chamber or hypotony a common complication? Is bleeding ever an issue?

Dr. Pro: Yes and you make a good point. There are short term and long term complications and many of those I listed above are longer term complications (complications that may happen later and/or last much longer). As with a trabeculectomy, a shallow anterior chamber, hypotony, or bleeding can happen. If this occurs, it is usually from the first day to two months after surgery.

P: Does the tube ever become obstructed, and if it does, what is the treatment?

Dr. Pro: Tube obstruction is a real problem. It happens for several reasons. First, the tube may be placed too close to the iris or not far enough into the AC (anterior chamber). Second, the IOP may go to low, and the AC may become shallow and the tube gets buried into the iris. Third, the tube can get blocked by blood or inflammatory material. In these instances the fluid cannot get out of the eye, the tube (drain) is clogged, and the IOP goes up.

What can be done? Sometimes the AC deepens on its own, or with the help of drops, or by the surgeon reforming the AC. This can free up the tube tip. Sometimes the tube needs to be surgically repositioned. In this instance, we often will flush the tube.

P: Dr. Pro, I had a Baerveldt drain placed in my ICE syndrome eye 10 months ago after my trab failed. The doctor says the tube is somewhat anterior and may have to be repositioned sometime in the future. What does he mean by anterior? Is this something I should be concerned about?

Dr. Pro: I think he means that the tube is too close to the corneal endothelium (inside of the cornea). This can sometimes cause the cornea to become cloudy.

P: Is tube blockage common? Does it occur right away or does it occur down the road?

Dr. Pro: Not too common, maybe in less than 2% of patients. Usually it occurs earlier on say if the anterior chamber gets shallow.

P: Are the complications the same for all implant devices?

Dr. Pro: They are probably the same for all the true tube shunt devices. This is a good time to mention the ExPress shunt, which is a very different device and works differently. The ExPress shunt is a small device made of surgical steel and it is used by some surgeons in a modification of standard trabeculectomy surgery. This device may help reduce the incidence of low IOP versus standard trabeculectomy surgery.

P: What percentage of implants suffer some complication?

Dr. Pro: With tube shunts, I think rate is close to 5% for some complication.

P: Is it common to have to continue or restart eye medications with shunts? And, does this signal a potential problem with the shunt?

Dr. Pro: This is very common. In fact in studies and in clinical practice, we regard control of the IOP as success, whether or not drops are still needed. This does not signal a problem with the shunt, but does point to how different individuals respond to glaucoma surgery. One individual may have a tube shunt and have controlled IOP, not needing drops, and another may need several drops to control the IOP after surgery.

P: What is the average life of a tube shunt with no complications?

Dr. Pro: That's a tough question to answer. The best we can say is that success may taper off over years. Studies often don't follow patients for over 1 year. The one year success of tubes is about 85%. Three year success in the TVT study was still 85%, which is promising and this illustrates another point. In glaucoma surgery often an operation will continue to function well if it has already been functioning well. That sounds strange but in practice when I have a patient return who is doing well at one year with no problems and a stable/controlled IOP, I expect that the operation will continue to function.

P: Why do some glaucoma doctors prefer shunt surgery to trab as the first surgery option in open angle glaucoma?

Dr. Pro: Well some surgeons have been influenced by the TVT study and have decided that a tube surgery is a safer or more effective surgery in his or her hands.

P: If the doctor decides to keep the patient on a steroid drop, does that mean that there is inflammation in the eye from the tube shunt or is it a preventive measure?

Dr. Pro: It could be either; some doctors feel that a low dose steroid may help prevent failure of a glaucoma surgery.

Moderator: What percentage of patients require additional surgery due to a complication?

Dr. Pro: Well, in terms of requiring another glaucoma surgery, five to fifteen percent of glaucoma surgery patients could require another glaucoma surgery because the first one failed.
It is rare to need to go back to the OR to deal with a complication from the tube shunt, and maybe less than five percent do.

P: Is conjunctivitis as dangerous for someone with a shunt as it is for someone with a trab?

Dr. Pro: Probably not. Sometimes we will advise a shunt in patients who are contact lens wearers, as we think there is less risk for an infection than with a trab for this group of patients.

P: Does the surgery change the appearance of the eye to others?

Dr. Pro: Sometimes. The most common complaint is related to the "patch" material that is used to cover the tube. This material helps prevent erosion of the tube through the conjunctiva. It is made out of donor sclera or pericardium that is completely sterile. The material is white and may be noticeable as a white, square area superimposed on the white of your eye. Sometimes the pupil can become distorted, and that can also be noticeable in some patients.

P: Is there long term pain or discomfort?

Dr. Pro: Long term pain is rare. Discomfort of some degree can happen after any eye surgery and is often related to the eye being more dry than it was before surgery.

Moderator: Thank you Dr. Pro and chatters! We hope to see you next chat.

Dr. Pro: You are welcome. Good night.

On April 21, Dr. Pro discussed Making Decisions" in the Chat room. Click here for highlights of that meeting.

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