Laser Surgery for Glaucoma
Chat Highlights
August 1, 2007

On Wednesday, August 1, 2007, Dr. Rick Wilson and the glaucoma chat group discussed "Laser Surgery for Glaucoma."

Moderator:  Welcome back, Dr. Wilson.

Dr. Rick Wilson:  Thanks.  I am now back on Philadelphia time, after attending the World Glaucoma Congress in Singapore.

Moderator:  Glad you had a safe trip.  What was the meeting about?

Dr. Rick Wilson:  The World Glaucoma Congress has merged with the International Glaucoma Symposium and this year’s meeting in Singapore provided expert teaching and skills-transfer to glaucoma specialists from around the world.

Moderator:  That sounds encouraging.  If you’re ready, we can start discussing the topic: laser surgery for glaucoma.

Dr. Rick Wilson:  There are many different types of laser surgery used in glaucoma. Most people think of the laser trabeculoplasty, in which the trabecular meshwork is injured by the laser beam and heals with increased outflow, as the most common laser surgery.  And it may be.  But most glaucoma specialists who do many trabeculectomies use the laser to cut the sutures holding the scleral flap over the hole in the wall of the eye that lets the fluid leak out slowly.  Cutting one of the sutures increases the rate of flow coming out.

Clearly, there is also the peripheral iridectomy for angle- closure glaucoma, and cyclophotodestruction of the ciliary body in recalcitrant (resistant to treatment) glaucomas.

P:   What is the difference between argon laser trabeculoplasty (ALT) and selective laser trabeculoplasty (SLT)?

Dr. Rick Wilson:  The SLT uses a different wavelength from the usual ALT.  That wavelength mainly is absorbed by pigment particles in the trabecular meshwork.  Because the laser isn't injuring the entire meshwork, the procedure is less damaging and offers the possibility that it may be repeated more often.

P:  My specialist in Perth (Australia) says that there is no proven difference between ALT and SLT.  That's why he hasn’t bought the newer SLT.  What is your opinion?

Dr. Rick Wilson:  The SLT definitely does less to the eye and may be safer, longer term, in that regard.  Your specialist is correct that the SLT has no better effect than the ALT.  To my knowledge, the ability to repeat the procedure effectively more than once has not been sufficiently proven.

P:  Why does age matter in the success rate of ALT or SLT?

Dr. Rick Wilson:  We don't understand what is causing the decreased outflow in the trabecular meshwork with glaucoma.  What is clear is that whatever mechanism is present in older patients with primary open-angle glaucoma (POAG) responds to the laser, whereas the mechanism present in younger patients does not.  But you are correct that the older the patient, the better the effect and the more pigment (dark color) in the trabecular meshwork, the better the effect.  Then, too, the diagnosis has to be primary open-angle glaucoma, normal-tension glaucoma, pigmentary glaucoma, or pseudoexfoliative glaucoma to get a good and lasting effect.

P:  What types of glaucoma fare better with SLT and what types fare better with ALT?

Dr. Rick Wilson:  Some surgeons feel that patients with pigmentary glaucoma and really dark pigment in the trabecular meshwork fare better with ALT than they do with SLT.  Otherwise, most patients who would do well with an ALT would also do fine with an SLT.

P:  Can you define "older" and "younger" in regard to the laser surgery question?

Dr. Rick Wilson:  I usually, mainly, treat patients over 60 years of age with the laser unless they have dark pigment in the trabecular meshwork.  The older they are, the better the effect.  Those who are 90 years old, and older, with primary open-angle glaucoma and good pigment in the trabecular meshwork, often get a 50% drop in IOP (intraocular pressure).

P:  What is the rate of complications with lasers?  Does the type of laser used increase or decrease the risk of complications?

Dr. Rick Wilson:  SLTs are more benign in terms of the visible effect on the trabecular meshwork, but the post-operative pressure spikes and inflammation do not seem much different.  An unexpected high rise in IOP about an hour after an SLT or ALT is a worrisome complication.  Most patients get a 4 to 8 mm Hg rise in IOP, which decreases by the next day.  A few patients, however, can get rises of 30 mm Hg or more.

P:  I have angle-closure glaucoma, for which I had laser surgery.  I don’t know what kind.  Whatever it was, it did not work for me.  I then had cutting surgery to lower the IOP, which is still high.  Can I have laser now for closed-angle glaucoma?

Dr. Rick Wilson:  You probably had a peripheral iridectomy in an effort to open your angle; apparently it was closed too long to help.  I surmise you then needed a trabeculectomy.  A laser trabeculoplasty would not work for you now because your iris is covering the trabecular meshwork and preventing access of the laser to the trabecular meshwork.

P:  For someone under age 60 (I'm 53), would it be better to have a trabeculectomy rather than laser?

Dr. Rick Wilson:  Unless I had pigmentary glaucoma, pseudoexfoliative glaucoma, or a lot of pigment in my trabecular meshwork, I would have a trabeculectomy performed by someone who does a lot of them.  I doubt the ALT or SLT would be effective for long.

P:  What is a CPC, what does CPC stand for, and when is it used?

Dr. Rick Wilson:  A CPC is a cyclophotocoagulation of the ciliary body.  A CPC uses the laser to destroy part of the ciliary body that makes the fluid in the eye.  If the trabecular meshwork is only letting out 50% of the normal amount of fluid and the surgeon cuts down production by nearly 50%, then it is hoped that equilibrium between the fluid that is produced and the fluid that exits the eye can be created with the help of eye drops.

P:  What is “laser ciliary body ablation” and when is that helpful?

Dr. Rick Wilson:  Laser ciliary body ablation is another term for CPC.  That type of procedure is usually a last-ditch effort for eyes that have failed a shunt, or are in such poor health that they would not survive a shunt.

P:  Sometimes ALT and SLT are described as "burning" the trabecular meshwork.  However, it's not really a burn, is it?  Can you tell us what takes place, either from a mechanical or chemical standpoint?

Dr. Rick Wilson:  It is a burn, especially in the case of the ALT.  Tiny burn scars can be seen years later.  The best theory of how the laser works is that the injury created by the laser stimulates the cells that should be cleaning up the debris in the drain and getting rid of it, but haven't been able to do a much better job.

P:  After two SLTs and one trabeculectomy, my pressures are great (7 mm Hg and 10 mm Hg).  However, a recent HRT (Heidelberg Retinal Tomograph) and a visual field test show continuing damage to the left eye and new damage to the right eye.  I am 74-years old. My Mother was legally blind at age 68, so I am ahead of the genetic game. My doctors feel that I am not getting an adequate blood supply to the optic nerve.  My carotid arteries are good. An MRI (magnetic imaging) with and without contrast shows no tumors or obstructions. What should I do next?

Dr. Rick Wilson:  It is impossible to advise you about such a complicated situation without seeing you.  However, I am not sure the HRT is accurate at that pressure and may be misleading. I have seen the first visual field after a trabeculectomy with good IOP control continue to decline for a few months before it stabilized.  I would do everything I could do to improve my health, e.g., exercise, nutrition, tight blood pressure and sugar control. I would continue to watch the visual fields carefully.  Make sure your corneas are not unusually thin and giving you lower pressure readings than you really have.

P:  You once said that, counter-intuitively, SLT was shown to be less effective in pigmentary glaucoma than in primary open-angle glaucoma.  If I am putting words in your mouth, please correct me.  Is there an explanation of why SLT would be so ineffective on angles with an abundance of pigment in them?  I have pigmentary glaucoma, with Grade four pigment in both angles.  Therefore, I was intrigued when I first read about SLT, but less so after your comment.

Dr. Rick Wilson:  The only word you just put in my mouth was “so” before ineffective.  As I mentioned earlier, some surgeons are using ALT in preference to the SLT in pigmentary glaucoma.  I found the effect with the SLT to be close to that with the ALT, but not better, as I had hoped.

P:  Earlier you said, "We don't understand what is causing the decreased outflow in the trabecular meshwork."  However, you also said that the laser may stimulate cells that should be eating up the debris in the drain. Is there debris in the drain?  Always?  Only in some cases, but not in others?

Dr. Rick Wilson:  There seems to be a build-up of glycosaminoglycans between the beams of the trabecular meshwork in primary open-angle glaucoma (POAG). In other kinds of glaucoma, there are other types of debris that build up, such as pigment, pseudoexfoliative material, white cells, etc.

P:  What criteria does an ophthalmologist use to determine whether to use ALT or SLT?

Dr. Rick Wilson:  Most doctors with an SLT use it instead of ALT on all trabeculoplasties, because it seems to be more benign.  That is what I did.

P:  How long does the decrease in IOP last after trabeculoplasty?  Does it increase slowly, or pop back up?  Does it ever go even higher?

Dr. Rick Wilson:  The IOP decrease may last only a few months, but can last up to five years or more.  Refer to what I said earlier about those who do well with laser trabeculoplasty, for the patients who should have both the best and the longest lasting effects.  Pseudoexfoliation is an exception to that, as the effect is more than for any other type of glaucoma, but the duration of effect will usually not last as long as it will for POAG.

P:  If ALT does not reduce IOP for a patient, will SLT?

Dr. Rick Wilson:  If the ALT is done well, the answer is almost always no.

P:  Are there any new lasers being researched?

Dr. Rick Wilson:  Yes, for both trabeculoplasty and trabeculectomy, but nothing is ready for patients.

Moderator:  Dr. Wilson, thank you so much for your time.

On August 15, Dr. Pro discussed "Glaucoma and the Elderly" in the Chat room. Click here for highlights of that meeting.

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