Risk-benefit Ratio for Surgical Intervention
Chat Highlights
May 24, 2006

On Wednesday, May 24, 2006, Dr. Rick Wilson, a glaucoma specialist at Wills, and the glaucoma chat group discussed "Risk-benefit Ratio for Surgical Intervention."

Moderator:    Welcome back to chat, Dr. Wilson.  Tonight our topic is "The Risk-Benefit Ratio for Surgical Intervention."  How is that ratio determined?

Dr. Rick Wilson:    It is a complex decision that balances the IOP (intraocular pressure) against the degree of damage to the optic nerve, and the patient's age and health, especially circulatory health.  Other considerations are: how well the patient is doing with medication, how much I trust the patient to be consistent with the medication, the patient's feelings about surgery, and how much risk the surgery will entail.  Eyes that have had previous surgery, or if the patient is on a blood thinner, increase the surgical risk.  Younger patients, especially those with dark irises and skin, have a less favorable prognosis for surgery, which has to be taken into account.

P:    Please explain what you mean by circulatory health.

Dr. Rick Wilson:  I mean the whole gamut of open or narrow arteries, hypertension, heart disease, how sticky the red blood cells are, whether vasospastic disease, like migraines, is present, and if the blood pressure is high enough.  Low blood pressure is a serious risk factor for glaucoma.

P:  So, non-compliance by a patient plays a role in the doctor's decision?

Dr. Rick Wilson:  Yes.  Non-compliance with medication is a good reason to perform a laser trabeculoplasty.  The post-operative medications are not as crucial to success as they are with a trabeculectomy.

P:  Why do dark irises have a less favorable prognosis for surgery?

Dr. Rick Wilson:  It seems the darker the pigmentation, the more scar tissue a patient forms, on average.

P:  Since a patient's physical health is important in making a decision about surgery, why do you think my ophthalmologist and my glaucoma specialist never asked about my blood pressure, etc.?

Dr. Rick Wilson:  That's hard to tell. It would be a good question for you to ask them.

P:  Which is more risky, a trabeculectomy or shunt surgery?  How long does each last?

Dr. Rick Wilson:  A recent study suggested that one year after surgery, trabeculectomy has slightly more complications than shunt surgery, and the shunts were lasting somewhat longer.  Shunts have little in the way of leaks and long-term infections, but the IOP is usually significantly lower with trabeculectomies.

P:  Do you think that study might persuade doctors to perform more shunts, rather than trabeculectomies?

Dr. Rick Wilson:  Yes. I think we will be thinking possible shunt surgery now on patients who do not require an IOP lower than 16 mm Hg (my bias).

P:  I asked about shunts because I may need one.  My pressures are ranging between 11 and 15 mm Hg. I am using three kinds of eyedrops and have had trabeculectomies.  I'm still losing vision.

Dr. Rick Wilson:  With IOPs of 11 to 15 mm Hg, it is unlikely that one shunt plate, no matter how large, would lower your IOP much further.  It would level it out, which might be all you need if you have an unsuspected IOP spike during the day or night.  A subsequent plate might be enough to get your IOP down to 9 to 12 mm Hg.

P:  Why do doctors mostly prefer to perform trabeculectomies first, instead of shunts? Is it only because of the lower IOP?

Dr. Rick Wilson:  That, and convention.  We were all trained to perform a trabeculectomy as our first-line surgery after laser trabeculoplasty, holding off on shunts until the trabeculectomy failed, or there was no more unscarred conjunctiva to work with for a trabeculectomy.

P:  If there's no more room because of several trabeculectomies, is there always room for a shunt?

Dr. Rick Wilson:  Usually, yes. The tube takes the fluid to a posterior plate at the equator of the eye, that is, half-way back.  Conjunctiva does not cover that area, as it is under the orbital rim. Therefore, scarring is less of a problem, although it can still hinder insertion of the shunt.

P:  Is laser surgery, trabeculoplasty, pretty much free of risk?

Dr. Rick Wilson:  No. Inflammation and IOP rises are occasionally seen.  But, if the patient selection is good, and the technique excellent, the risks are slight and the results fairly good.  Most of the time, when doctors perform trabeculoplasty on patients who have little chance of success, they get into trouble.

P:  What are the chances that more than two SLTs (selective laser trabeculoplasty) will at some point be considered safe or worth trying?

Dr. Rick Wilson:  I'd say the chances are 50-50, but would depend upon how much time has elapsed between SLTs.

P:  If or when the effect of ALT (argon laser trabeculoplasty) or SLT wears off, do intraocular pressures soar beyond pre-surgical levels?  In other words, does trabeculoplasty ultimately damage whatever function the trabecular meshwork may have had in the first place?

Dr. Rick Wilson:  Good question.  The newer SLT is much less damaging than the ALT.  When the effect is lost, the IOP may return to a rising line that was interrupted by the laser.  Whether the pressure starts on the line where it stopped, or hits the line that much later in time -- therefore, higher on the line -- is not clear.

P:  I understand that in England, trabeculectomies are often a first-line treatment. Is that largely a matter of convention?  What do other countries with socialized medicine do?

Dr. Rick Wilson:  I think that varies considerably.  I would think that in England, with the advent of prostaglandins, they might stick with medication a little longer than they once did.  The original practice started because several studies in England showed that patients initially operated on did better than those having medication and laser treatment.

P:  I am a 55-year-old female with controlled hypertension.  In January and March of 2005, I had bilateral trabeculectomies.  Now the pressure in the eye that had the surgery in March is up to 30 mm Hg. I am using Lumigan in that eye, and I've been told I need to have the bleb needled. Any thoughts, comments, or words of encouragement?  Any advice about the recovery period, risks, result percentages, etc?

Dr. Rick Wilson:  My thoughts, comments, and words of encouragement vary considerably, depending upon how the surgeon does the procedure and what his past results have been with that technique.  Usually, a surgical revision of the bleb has at least a 50% chance of working when 5-FU or mitomycin-C is used.  The complications are usually transient, but I have had a couple of patients with too low an IOP long term.

P:  What are my options?

Dr. Rick Wilson:  I would think your options are medicine, needling, a repeat trabeculectomy, or a shunt.  However, if your optic nerves look damaged and the IOP is at the top of normal, I can see how your glaucoma specialist could get nervous and want to put you in a safer IOP zone.

P:  Does surgical intervention pose different risks for different kinds of glaucoma?

Dr. Rick Wilson:  Yes.  Neovascular glaucoma is very difficult to deal with. Inflammatory glaucomas are slightly less difficult, but still more difficult than usual.

P:  What are the chances of a cataract forming immediately after a trabeculectomy?

Dr. Rick Wilson:  Usually, patients who already have a cataract see their cataracts worsen at a faster rate than the cataracts were before surgery.  It is usually only with the complication of choroidal detachments and very low IOP post-operatively that the eye does not make enough aqueous to supply the lens with oxygen and nutrition.  Then a cataract forms quickly.

P:  Haven't you said that there is not much point in doing cataract surgery before the cataract causes the patient discomfort and difficulty seeing, especially if there are other eye problems that make the surgery more risky?

Dr. Rick Wilson:  Yes.  Cataract surgery should be done, as a general rule, when patients finds the decreased vision a hindrance, preventing them from doing something they want to do, and not just a nuisance.

P:  My two-year-old daughter was born with glaucoma, has had 11 operations, and has not really had any stable eye pressures.  (Her pressures -- right eye, 18 mm Hg; left eye, 16 mm Hg -- are now trending toward normal.)  If her pressures don't stabilize, what would be the benefit of say, a trabeculectomy instead of Ahmed valves (replacements, revisions, etc)?  Her cupping was .7 right and .5 left, with some peripheral vision lost.

Dr. Rick Wilson:  After that many surgeries, it may not be possible to do a trabeculectomy, as there may not be any virgin conjunctiva.  If the IOP rises again and there is good conjunctiva, perhaps a trabeculectomy should be considered.

On May 31, Dr. Henderer discussed "Optic Nerve Imaging: Past, Present and Future" in the Chat room. Click here for highlights of that meeting.

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