Early and Late Complications of Trabeculectomies
Chat Highlights
November 2, 2005

On Wednesday, November 2, 2005, Dr. Rick Wilson, a glaucoma specialist at Wills, and the glaucoma chat group discussed "Early and Late of Accompanying Trabeculectomies."

Moderator:  Hello, Dr. Wilson. The topic tonight is one you suggested:  Early and Late Complications Accompanying Trabeculectomies.

Dr. Rick Wilson:    While this evening’s chat concerns potential complications with trabeculectomy (filtering surgery), it should be remembered that surgery is not suggested unless the risk-benefit ratio clearly favors surgery.  If the visual field or optic nerve is suffering progressive damage, or the IOP (intraocular pressure) is at a level that assures nerve damage will ensue, then there is close to a 100% risk of slowly losing vision to glaucoma, versus a more immediate, but much less frequent risk with surgery (usually in the low single digits).

P:  Sometimes the progression of optic nerve damage is difficult to verify with a visual field test. In such cases, how does the doctor determine the risk-benefit ratio?

Dr. Rick Wilson:  The doctor and the patient must look at all the objective evidence and make the decision.  Often we have to play the odds:  the risk of progression versus the risk of the surgery.

P:  Despite complications, I'm glad I had a trab (trabeculectomy).

Moderator:  Same here.

P:  Not here.

Dr. Rick Wilson:  It's important to understand that trabeculectomy is not a really predictable procedure.  The surgeon makes a flap of sclera that is 1/3 the thickness of the sclera.  Under the flap, the surgeon makes a hole in the eye, and usually removes a piece of iris to prevent it from moving into the hole and blocking it.  The flap is loosely sewn down with multiple sutures to make the aqueous fluid "filter" out of the eye slowly.

P:  What are the most common complications immediately after a trabeculectomy?

Dr. Rick Wilson:  Any bleeding, or even oozing of serum, under the flap will seal it down and cause the IOP to spike up.  It is also common for the flap to let out more fluid than it seemed when the patient was on the operating table, and for the pressure to be too low.  Think about it as a bell-shaped curve.  If I do 100 trabs the exact same way, they will result in a spectrum of results. Most of patients will obtain a suitable pressure.  Some of patients will have failed trabs.  Others will have trabs that work too well, and the IOP is too low, resulting in blurred vision.

P:  How often does hypotony occur after a trab?

Dr. Rick Wilson:  The most common complication immediately after a trab is an IOP that is too high or too low.  If the IOP is too high, usually a suture holding down the flap is cut with a laser or needle, if there is a releasable suture.  That opens up the flap wider, allowing more fluid to escape, resulting in a lower IOP.

P:  What could cause hypotony (an IOP of 2 to 3 mm Hg) four weeks after a trab?  How long is it okay to leave the pressure that low?  The anterior chamber is deep, the bleb looks good, and there are no retinal problems.  What is the best course of treatment?

Dr. Rick Wilson:  If the pressure is too low, I usually wait see if it will come up before deciding on any type of surgical revision. It depends upon the vision.  If the vision is acceptable, as it might be in someone who is over age 75 and has a stiff eye wall, then I would declare victory and be happy.  If the vision is decreased to an unacceptable level, then, usually, six to ten weeks postoperatively, the trab is revised and more sutures are put in the flap to raise the IOP and improve vision.

P:  What is an adjustable suture? Do you use them?

Dr. Rick Wilson:  I invented one kind of adjustable suture that allows the surgeon to tighten the flap suture if he or she has loosened it too much.

P:  At the moment the hole is made, does the IOP drop to zero?

Dr. Rick Wilson:  It drops to atmospheric pressure, which is 0 mm Hg on the tonometer.  But the flap is promptly sewn down and provides resistance, so the IOP should start to rise on its own.  However, we always fill the anterior chamber to help the eye along.

P:  What pressure is too low? What is the normal range of IOP?

Dr. Rick Wilson:  Normal eye pressure is 12 to 22 mm Hg.  The IOP is too low if it causes the sclera, or outer wall of the eye, to shrink.  The sclera is slightly elastic, but the middle layer (the choroid), and the inner layer (the retina) are not.  When the sclera shrinks, the retina can get small folds in it.  That causes distorted and blurred vision.

P:  If the retina gets folds, can the doctor detect it?  Would I be able to see it if I look at my eye in the mirror?

Dr. Rick Wilson:  The doctor can detect it by looking with special instruments.  The patient would not be able to see the folds in her or his retina.

P:  I get confused about the flaps.  When you say the flap lets out more fluid and the pressure gets too low, do you mean the scleral flap or the conjunctival flap?

Dr. Rick Wilson:  I haven't talked about the conjunctiva yet, so it is the scleral flap.  The scleral flap is made under a conjunctival (the clear surface layer of the eye) flap.  Complications can occur at this layer, with tears, holes or rips during surgery and cause too low an IOP early on.

P:  If the first trab on one eye is unsuccessful, is it worth doing a trab on the other eye?  What are the chances of success?

Dr. Rick Wilson:  That depends upon how well the first trab was done, and whether mitomycin was used to suppress scarring the first time.  If the surgery could be done better or with more anti-scarring medication, then I think usually it would be worthwhile to repeat it. If neither were true, I would move to an aqueous shunt.

P:  What complications are common, but usually resolve without big problems?

Dr. Rick Wilson:  A side effect, not really a complication, would be blurred vision and a dry mouth if atropine drops are used post-operatively.  The eye is usually red post-operatively, but that improves over time.

P:  Can vision actually improve after a trab or does it usually get worse?

Dr. Rick Wilson:  If there is corneal swelling from high pressure, or the nerve is severely damaged, the vision may get better after surgery.  In my patients, the average vision result is a loss of 1/2 line on the Snellen chart at one year.  That is usually due to cataracts forming at a faster rate than would have happened naturally.

P:  What is an encapsulated bleb?

Dr. Rick Wilson:  An "encapsulated" bleb is a misnomer.  A bleb is the elevation in the conjunctiva overlying the trabeculectomy flap, that is, where the aqueous is coming out and pushing up the conjunctiva.  An encapsulated bleb has no capsule (i.e., lining).  It seems the fibrous wall of the bleb gets pushed together or compacted, and it markedly decreases the rate of aqueous passing through it to be absorbed into the body.

P:  Five weeks ago I had a trab, a choroidal bleed a couple of days later, and hypotony for a couple of weeks.  Now things seem to be improving.  My IOP is 8 to 12 mm Hg and my vision is 20/25 (and even a little of the 20/20 line).  What late complications should I be on the lookout for?

Dr. Rick Wilson:  A major late complication is cataract formation, which as I said earlier happens at a faster rate than would occur without a trabeculectomy.  Another late complication can be a gradual thinning of the conjunctiva making up the bleb over time, usually two to many years.  The thinned conjunctiva may leak, form a hole, or get infected.  An infection that gains access to the inside of the eye is very dangerous.

P:  How serious is an infection? Can it lead to blindness?

Dr. Rick Wilson:  Yes. Post-operative patients should be aware of the pneumonic "RSVP," which stands for Redness, light Sensitivity, Vision change and Pain.  Any of these symptoms should alert you that a potential infection may be occurring.

P:  I had those symptoms with aqueous misdirection.  I knew what to look for and did not hesitate to call my doctor.

P:  I have trabs in both eyes, eye pressures are now reasonably stable in their 20's, but I still don't have any useable sight.  My specialist thinks that some optic nerve remains, but he is at a loss to explain why I haven no useable vision.

Dr. Rick Wilson:  If you have optic nerve damage, IOPs in the 20's are still far too high.  Without seeing you, I cannot venture a reason for your lack of sight.  Perhaps a second opinion with another glaucoma specialist would be reasonable.

P:  If a trab is successful, with no complications afterwards, is there a time when the pressures will stabilize?

Dr. Rick Wilson:  There is a time, but it varies with everyone.  Usually, by three months the healing has slowed down significantly.  Over time, as the bleb thins noticeably, the IOP may even start to drop.

P:  How invasive is surgery to add sutures six to ten weeks after a trabeculectomy?

Dr. Rick Wilson:  It is delicate surgery, but because it is outside the eye, working on the surface, it is not an extensive procedure.

P:  I have ICE (irido-corneal endothelial) syndrome.  I used atropine for four weeks, but have not used it for three.  My pupil size has gone down a little, and reacts to light, but is still fairly large.  Is there a chance the size of my pupil will return to normal?

Dr. Rick Wilson:  With ICE syndrome, the membrane from the lining of the cornea often constricts and pulls open the pupil.  I am not sure the atropine had any lasting effect on the pupil.

P:  I realize the atropine might not be causing the pupil to be large.  I'm concerned that, because of the reason you mentioned, it will not return to its normal size.  The doctor said I could try a pupil- shrinking drop, but we will wait a month to see if it gets any smaller.  Is it possible because of the ICE that my pupil will just stay large?  It reacts to light, so I'm not sure if that is good.

Dr. Rick Wilson:  I'm concerned as well that it may stay large, because it is pulled out by the ICE membrane.  It is good that it reacts to light.

Moderator:  This is for a patient who could not be here.  Age 59.  Normal-tension glaucoma. Excellent health.  Moderate damage to the optic nerve.  No real improvement after SLT (selective laser trabeculoplasty) in left eye.  IOP of 19-20 mm Hg.

P:  Is non-penetrating, deep sclerectomy or viscocanalostomy an option? How about a trabeculectomy?  Which of the two has a higher rate for unwanted healing or closing after surgery?

Dr. Rick Wilson:  That varies according to the surgeon. Some surgeons have perfected non-penetrating filtration surgery, so that they can get IOPs in the 13 to 14 mm Hg range.  That's at the top of where you probably need to be.  Most surgeons, however, have not, and non-penetrating surgery results in IOPs in the 17 to 18 mm Hg range, which is not low enough for someone with "low- tension glaucoma."

P:  How many months after a trab with a good functioning bleb before you can say the surgery was a success?

Dr. Rick Wilson:  Three or more months.

P:  Is there any long-term downside to using mitomycin C?  How long has it been used for trabeculectomies?

Dr. Rick Wilson:  As I remember, mitomycin C was used in Taiwan for several years, probably starting in the late 1980's, before it was used here.  There is a noticeable increase in the late-term leaks and infections with its use.  The migration to using conjunctival flaps hinged back toward where the lining of the lid meets the conjunctiva on the ball of the eye, rather than hinging the flap at the limbus (where the sclera meets the cornea), has helped noticeably decrease the late leaks and infections.

P:  How long after a trab will the normal redness be completely gone?

Dr. Rick Wilson:  Five to eight weeks, as a rule.

P:  Recently, my brother, who is 50 years old, learned that the trab he had two years ago has scarred over.  When his trab was done, 5FU was used.  Is it common for trabs to scar over that soon?

Dr. Rick Wilson:  It used to be said that the average trabeculectomy lasted for seven years.  I think we do better than that now.  Still, it is not too unusual for a trabeculectomy to scar over like your brother's.

P:  Two weeks ago I had a trab in my right eye.  When I blink, a patch of cloudiness comes into the vision of my right eye.  When I tilt my head back, look at my right eye in the mirror, lift the upper lid and try to blink, I notice the edge of what seems like a thin clear film extending down from underneath my right upper eyelid.  My doctor doesn't seem to be concerned about that, but I am.  What could it be?

Dr. Rick Wilson:  The clear film that comes down from underneath your lid may be the thin conjunctiva and would be entirely normal.  Again, I can't tell without seeing it. Good night all and have a great week.

Moderator:  Thank you, Dr. Wilson.

On November 9, Dr. Wilson discussed "Congenital and Developmental Glaucoma" in the Chat room. Click here for highlights of that meeting.

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