Incisional Surgery Risks
Chat Highlights
August 6, 2008

On Wednesday, August 6, 2008, Dr. Michael Pro, a glaucoma specialist at Wills, and the glaucoma chat group discussed "Incisional Surgery Risks".

Moderator: Tonight's topic is "Incisional Surgery Risks." What can you tell us to begin with about those risks, Dr. Pro?

Dr. Pro: Let’s divide incisional surgery a bit. In glaucoma the two most commonly performed procedures in the United States are trabeculectomy (trab) and tube shunts. Currently, trabs are performed about four times more often than tubes, but tubes are becoming more common.
So I will start with trabs, which have a much longer track record. Complications that may result from this surgery include early and late bleb leaks, blebitis and endophthalmitis (infections), hypotony (low IOP), flat anterior chambers, choroidal detachments (swelling or bleeding behind the retina associated with low pressure), retinal detachments, corneal edema, and permanent visual loss.

The list for tube shunts is similar, but they are much less likely to suffer a bleb leak (as there is really no bleb near the cornea), but tube shunts increase the risk of corneal edema, also erosion of the tube may occur. Diplopia (double vision) is also described with tube shunts.
And finally, both procedures increase the risk of developing cataracts.

P: That's a long list of risks doctor! How should we as patients weigh these risks in considering surgery?

Dr. Pro: Patients should be aware that the risks of surgery are generally outweighed by the benefits. Surgery to lower the IOP has been shown in multiple large-scale studies to delay or stop the progression of glaucoma and thus preserve vision, which is the ultimate goal.

P: What can the patient do to minimize the risks? Are there any healthy things we can do to be in better "shape" for eye surgery?

Dr. Pro: Sure, it is best to treat dry eyes and severe blepharitis prior to surgery, because an already irritated eye is likely to become more so after surgery.

P: Is bleeding during incisional surgery considered to be a complication?

Dr. Pro: Not if the bleeding is just on the outside of the eye or minor (light) bleeding within the eye.

P: I know that scar tissue can grow around tube shunts and obstruct their functioning. Once scar tissue is removed does it come back? How long is the valve able to work effectively?

Dr. Pro: Yes, scar tissue can re-grow and it can be tough to say exactly how long a tube shunt can work. In general studies show that about 50 percent of patients continue to have success at five years, but I find that a good prognositic indicator is the appearance of the patient approximately one year from surgery. If the bleb or conjunctiva looks white and quiet—that is, if the bleb does not appear red and inflamed—and the IOP is controlled, often the tube or trab will continue to function nicely for years. On the other hand if the eye is red, has bouts of inflammation, or has wide IOP fluctuations between visits, the outcome of the surgery may not be as successful.

P: If a tube shunt doesn't work out because of complications such as tearing and irritation, is it possible to remove it? And is there an alternative?

Dr. Pro: Sometimes the eye may be irritated after shunt surgery due to secondary dry eyes. The shunt may be causing a patch of dryness on the cornea that is leading to the reflex tearing. If so, conservative therapy such as artificial tears may help. In other situations, the shunt may need to be re-positioned or even re-moved. I do shunt re-positions in cases where the cornea is affected (corneal edema) due to the tip of the tube coming too close to the inside of the cornea. Complete shunt removal is very rare and usually necessary only in cases of infection or exposure intransient to surgical measures to re-cover the tube with epithelium.

P: This is a follow-up to shunt question above (It was my son who had the shunt). It's been three months since the surgery; is that a factor? The size of the shunt is also large and looks 'blocky'. Eye Movement is also a problem.

Dr. Pro: In children the healing can be quite different than an adult. Often the inflammatory response is increased, but it is possible in some persons to see the area of drainage under the lid. As to eye movement and double vision, it should improve after the surgery. If there is no improvement is may be wise to be seen by a pediatric ophthalmologist who specializes in eye movements.

If the shunt is working and the IOP is better, your glaucoma specialist may not want to remove it, but prefer to wait and see.

P: This question was received via email: According to the Ophthalmic Technology Assessment of the American Academy of Ophthalmology on aqueous shunts in glaucoma, published this spring, the major long term complication of shunt surgery is the corneal endothelial cell loss. In that event they suggest that even if the surgery happened years ago, it is advisable to reposition the tube from the anterior chamber to the vitreous cavity (after vitrectomy). This consensus report doesn't say what the level of damage is, in what speed it occurs and what it means in terms of vision (loss). Have you any experience with this? Can you please elaborate on this?

Dr. Pro: Sure, it makes sense to place the tube as far back from the cornea as possible, but putting it in the vitreous cavity is impossible in someone who has not had a vitrectomy. Also, vitreous tube placement may be difficult for some anterior segment surgeons who are not as familiar with the posterior anatomy. I currently consider vitreous cavity tube placement in patients who are vitrectomized, but do not move the tubes of persons who had a successful shunt surgery, but then later have a vitrectomy. In my mind each additional surgery risks complications, such as infection, bleeding or shunt failure, that outweigh the risk to the cornea from leaving the tube in place.

P: What is the average success rate of the trab? If someone is 47 with blue eyes and SLT didn't work, would you adjust the success rate lower?

Dr. Pro: The average success at one year with anti-metabolites is about 80% at one year, dropping to about 50% at 5 years. Having an SLT prior does not reduce the success. Having blue eyes is not associated with success or failure, but higher failure rates are seen in African Americans.

P: My son was told he was not a good candidate for another trab due to having had numerous trabs and limited tissue being available for a new one. Is there any other method of eye surgery available if the shunt is removed? He is becoming increasingly depressed. This was his first shunt and the results are not like his past trab surgeries.

Dr. Pro: Sometimes we proceed to cyclophotocoagulation procedures in patients who have failed trabs and tubes. But it is also possible that a second tube shunt can be considered.

P: Does the age of the patient affect the chance of a risk occurring?

Dr. Pro: Well I always have thought that, but one recent study I found about suprachoriodal hemorrhages did not find that. Allow me to show you that...

Of a total of 2285 glaucoma filtration procedures, 66 (2.9%) cases of delayed suprachoriodal hemorrhage were identified. It developed in 9 of 615 (1.5%) trabeculectomies without anti-metabolite, 30 of 1248 (2.4%) trabeculectomies with anti-metabolite, 2 of 72 (2.8%) valved tube shunt implantations, and 25 of 350 (7.1%) non-valved tube shunt implantations. a. Risk factors were anti-coagulant usage, white race, post-operative hypotony, and aphakia or anterior chamber intraocular lenses. Visual outcomes were often poor. (From Tuli et al. Delayed suprachoroidal hemorrhage after glaucoma filtration procedures. Ophthalmology. 2001 October.)

P: Does the use of mitomycin (MMC) during trab surgery shorten the length of time the trab works?

Dr. Pro: No, it makes it last longer.

P: Since a trab does not last forever, multiple surgeries will be in the future of a patient if he/she has at least 30 years of life left. Do you just continue surgeries until there is no vision left to be saved?

Dr. Pro: To be honest, in clinical practice we often find success with the second or third surgery should the first fail, The goal is to delay the progression of glaucoma, and in some advanced cases my patients and I will decide that further surgery is unlikely to improve the person's quality of life and be hold off.

P: Isn't the effect of cyclophotocoagulation blindness, besides lowering pressure?

Dr. Pro: About 10% of patients had vision that was one line worse after CPC. But that study may have been flawed by looking only at people who already had advanced disease; those people may be more likely to have worse vision after any surgery.

P: What is the usual "after-care" for a trab or a shunt? How long before your vision returns to what it was before the surgery?

Dr. Pro: I tell my patients that the vision may be worse for up to a month, but for most patients the vision is coming back to pre-operative levels before then. The "after-care" is a regimen of antibiotics for a week or so, steroids for one month or more, and restrictions on strenuous activity or work for several weeks post-op.

P: What is the ratio of eye surgeries done that do not meet their desired outcome?

Dr. Pro: Well, that can be hard to answer because the target is different from one paper to the next, so I think the success rate of 80 percent at one year is generally true.

Moderator: It's half past the hour Dr. Pro. Thanks so much for taking the time to be with us.

Dr. Pro: Well I thought it was a good discussion! Good night.

On August 20, Dr. Pro discussed "Optic Nerve Imaging" in the Chat room. Click here for highlights of that meeting.

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