Lasers for Glaucoma
Chat Highlights
September 3, 2003

Norma Devine, Editor

On Wednesday, September 3, 2003, Dr. Rick Wilson, a glaucoma specialist at Wills, and the glaucoma chat group discussed "Lasers for Glaucoma."

P:  What is the difference between the selective lasers and the other lasers?     

Dr. Rick Wilson:  The frequency of the selective laser is such that, if used at a low power, it is only absorbed by the melanin granules in the trabecular meshwork.  The ability to use low power and still get adequate results helps to reduce side effects and complications and possibly allows the SLT to be performed more than once or twice.

P:  Why does ALT fail in younger patients?  Why might  a glaucoma doctor choose to use  ALT during the initial visit of a 17-year-old patient with a pressure of 40 mm Hg?

Dr. Rick Wilson:  We don't know why younger patients do not respond well to ALT.  I'm sure it has a lot to do with the mechanism of their glaucoma.  I don't know why the doctor you mentioned chose to use ALT in that patient.  

P:  How many laser burns are usually made with a SLT?  I think I had 95 zaps.

Dr. Rick Wilson:  Usually, there are 50 burns with a SLT and 70 to 100 burns over 360 degrees with an ALT.  

P:  Is that 360 degrees in the eye?  Or is that the laser temperature?

Dr. Rick Wilson:  The term, "360 degrees of treatment," means treatment around the whole eye.

P:  If a patient with normal-tension glaucoma (specifically, an intraocular pressure (IOP) of 19 mm Hg) is still losing vision, will a trabeculoplasty help? 

Dr. Rick Wilson:  Argon and selective laser trabeculoplasty seem to work very well in patients with normal-tension glaucoma.  These two types of laser usually lower IOP by approximately 30%, if the patients are carefully chosen.  It does not seem to matter whether the IOP is 60 mm Hg or 12 mm Hg, the 30% drop still holds true.  It is hard to reduce pressure from 12 to 8 mm Hg with medication, but easy to reduce it from 60 to 40 mm Hg. That is why the laser is so useful in normal-tension glaucoma. 

P:  What kind of laser is used to cut sutures (stitches)?  

Dr. Rick Wilson:  A Krypton (red) laser is used after a trabeculectomy to cut sutures when there is blood under the conjunctiva.

P:  Would laser be used for an acute angle-closure attack in a young person?

Dr. Rick Wilson:  In an angle-closure attack, a hole needs to be made in the iris.  That is best achieved with the Nd:YAG laser.  The age of the patient is not relevant.

P:  What kind of laser is used for cyclophotocoagulation?

Dr. Rick Wilson:  A fifth type of laser, the diode laser, is most commonly used for burning the ciliary processes so they no longer make fluid.  The goal is to burn about one half of the ciliary processes so the IOP is not brought down too far.

Moderator:  Are there risks involved with lasers?  If so, what are they?  Are some lasers more risky than others?

Dr. Rick Wilson:  There are risks with all of the lasers.  The SLT seems to have the least long-term risk.  However, it can cause just as much of a postoperative pressure rise as the ALT.  All of the lasers can burn the wrong tissue if aimed improperly.  Postoperative pressure rises and inflammation are the most common side effects associated with lasers.

P:  How often do patients get a mild to moderate iritis following SLT?

Dr. Rick Wilson:  All patients get a small amount of inflammation following laser surgery.  However, I think a visible iritis is unusual.

P:  I have had cataract surgery in one eye and will need it in the other eye in the future.  What effect, if any, would SLT have?

Dr. Rick Wilson:  In a person who is older -- especially older than 65 years of age -- has good pigment in the trabecular meshwork, and has an open angle, the result should be good.  If the cataract surgery is somewhat complicated, the laser might not work as well.

P:  How long has SLT been used as a glaucoma treatment, and what are the known side effects? 

Dr. Rick Wilson:  Dr. Mark Latina has been performing SLT for at least five years.  We have been doing it at Wills over a year.  The side effects look no worse than with ALT.    

P:  After my trabeculectomy, my doctor used a laser to cut the stitches.  Is the same type of laser used for iridectomies?

Dr. Rick Wilson:  Yes, usually the argon laser is used for cutting sutures.  However, the krypton laser is used when there is blood under the conjunctiva.

P:  Is ALT advocated as part of the treatment regimen for patients with uveitis-related glaucoma?

Dr. Rick Wilson:  No, because the mechanism in uveitis-caused glaucoma is a blockage of the trabecular meshwork by white cells, and laser trabeculoplasty does not seem to be effective for this type of glaucoma.

P:  What are the results if laser is used to treat a patient with uveitis-related glaucoma?  

Dr. Rick Wilson:  Usually there are no positive results, but if much energy was used, there may be a pressure rise and more inflammation.

P:  How often can SLT be repeated?

Dr. Rick Wilson:  Theoretically, repeating SLT is possible, but there is not enough experience with its use to know the answer to your question.

P:  You mentioned the possibility of lasers burning the wrong tissue.  I though SLT was more or less self-guided, in that it is effective only on melanin granules in the meshwork.  Please comment.

Dr. Rick Wilson:  It's true that it's only effective on the melanin granules, but the laser should only be aimed at the target tissue.

P:  If the wrong tissue is burned by a laser, can that be repaired?  

Dr. Rick Wilson:  No, not after the laser has burned tissue.

Moderator:  Can a doctor tell if he or she burned the wrong tissue?

Dr. Rick Wilson:  Yes, the doctor should be able to see the effect of the laser on the tissue.

P:  How long after SLT does the pressure remain down, and when it fails, is the pressure rise sudden or gradual?  

Dr. Rick Wilson:  The effect of the SLT over time is quite variable.  Some patients get a good result for three to five years;  others just for a few months.  When the laser fails, the pressure usually rises slowly.  In pseudoexfoliation, the pressure is said to rise more quickly.

P:  When SLT fails, does the patient return to using eye drops or have more surgery?  

Dr. Rick Wilson:  Usually, the SLT is used like a strong medication, adding it to other medications.  If the laser fails and there are no other medications to use, the patient has to turn to surgery.

P:  Are laser treatments becoming more of a first-line therapy for some patients, rather than eye drops?  

Dr. Rick Wilson:  Not yet among the glaucoma specialists.  With prostaglandins being as effective as they are, most glaucoma specialists will start with a prostaglandin or possibly a beta-blocker.  If the effects are not as good as they wanted, then they might turn to a trabeculoplasty.

P:  Can SLT make your vision worse?

Dr. Rick Wilson:  Yes, if you have advanced glaucoma (an enlarged cup and a lot of visual field damage) and your pressure increases after the laser treatment.

P:  Do you ever consider endocyclophotocoagulation in a patient who has several tube shunts that have scarred over, but still has most of the vision that he or she started with?

Dr. Rick Wilson:  That is a tough decision.  I usually would try to increase the outflow of fluid from the eye, rather than cut down on the fluid the eye makes.  Increasing the outflow is a more natural effect for the eye.  However, if I have already revised the shunt once, or if the patient has only one eye, a third plate is in place, and the pressure still is not controlled, then I would do a cyclophotocoagulation, either from the inside or the outside. 

P:  Can cyclo-cryotherapy (freezing) be repeated?

Dr. Rick Wilson:  Yes.  My record is eight cyclo-cryo therapies.  But that was many years ago when cyclo-cryotherapy was used instead of laser cyclophotocoagulation.

Moderator:  Thank you, Dr. Wilson, for answering our questions. 

Dr. Rick Wilson:  Thank you all for a good chat.  I hope you have a great week and we will see you back next week to talk about glaucoma and the lens.

End of highlights for September 3, 2003.

On September 10, Dr. Wilson discussed "Glaucoma and Disorders of the Lens" in the Chat room. Click here for highlights of that meeting.

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