Laser Treatments
Chat Highlights
October 2, 2002

Norma Devine, Editor

On Wednesday, October 2, 2002, Dr. Rick Wilson, a glaucoma specialist at Wills, and the glaucoma chat group discussed "Laser Treatments."

Moderator:  Dr. Rick, patients often get confused by the terminology when the words sound similar, such as trabeculectomy and trabeculoplasty. Could we start with an explanation of those two terms?

Dr. Rick Wilson:  Laser surgery for open-angle glaucoma is called a trabeculoplasty, and involves making microscopic burns in the trabecular meshwork.  A trabeculectomy is cutting surgery that creates a flap valve on the top (superior) part of the eye.

P:  Are there different types of laser surgery for different types of glaucoma?  

Dr. Rick Wilson:  The trabeculoplasty is used for open-angle glaucoma.  A peripheral iridectomy and a gonioplasty are used for narrow-angle or angle-closure glaucoma.

Moderator:  What is done during a peripheral iridectomy?     

Dr. Rick Wilson:  In a peripheral iridectomy, a small hole is made in the iris to equalize the pressure behind and in front of the iris.  Equalizing the pressure  eliminates the forward bowing of the iris that has pushed it closer to the trabecular meshwork. 

Moderator:  And what about a gonioplasty?

Dr. Rick Wilson:  A gonioplasty shrinks the peripheral iris by the drain and pulls it away from the trabecular meshwork.

P:  How long, on average, does the effect of a gonioplasty last? 

Dr. Rick Wilson:  In my experience, about three years.  The same effect can often be achieved with pilocarpine.

Moderator:  Are there different types of laser surgery just for closed-angle glaucoma?

Dr. Rick Wilson:  If the angle is recently closed, either an iridectomy or gonioplasty may help.  If the angle has been closed too long, a goniosynechiolysis or a trabeculectomy will be needed.

Moderator:  What is a goniosynechiolysis?

Dr. Rick Wilson:  A goniosynechiolysis involves mechanically pushing the iris off the trabecular meshwork to open the drain. An iridectomy is performed before goniosynechiolysis. 

Moderator:  Are there different types of laser surgery for open-angle glaucoma?

Dr. Rick Wilson:  There is only one major kind of laser surgery for open-angle glaucoma. The selective laser trabeculoplasty (SLT) is just an argon laser trabeculoplasty (ALT) done with another wavelength, which is kinder and gentler to the trabecular meshwork.

P:  Can laser surgery be performed on a patient with recurrent uveitis?

Dr. Rick Wilson:  A trabeculoplasty would probably do little for someone with uveitis, because the underlying problem is the backup of debris from inflammation in the drain of the eye. 

P:  How do you know how much power is required?  Does the laser have a power control?  Do you test the laser before each surgery for the appropriate power level?

Dr. Rick Wilson:  The laser does have a time, power, and spot-size control.  We usually start low and look for just a minimal effect.  Laser is light energy, so some pigment is needed to absorb the laser energy with the argon and, to a lesser extent, with the selective laser trabeculoplasty. 

P:  Where does the pigment come from? 

Dr. Rick Wilson:  The pigment is usually brown or black and comes from the back of the iris in the posterior trabecular meshwork (PTM.) Even blue irises have brown or black pigment on the back.

Moderator:  What does the laser do to the trabecular meshwork?

Dr. Rick Wilson:  Laser surgery for open-angle glaucoma (trabeculoplasty),  involves making microscopic burns in the trabecular meshwork.  One theory about why this treatment works is that the laser beam shrinks an area of tissue.  That action pulls open the holes in the drain immediately surrounding the burns, allowing more fluid to leave the eye.  Another theory is that the injury of the laser burn itself stimulates cells in the trabecular meshwork to clean up the accumulated debris that has been blocking the drain.

P:  Is laser surgery ever used in children for treating congenital glaucoma?

Dr. Rick Wilson:  A different type of laser that cuts, rather than burns, has been used.  But the holes created lasted too short a time to be useful.

P:  How often will you repeat a trabeculoplasty?

Dr. Rick Wilson:  If the laser surgery is effective, the amount of intraocular pressure lowering slowly diminishes over time.  Little effect remains in most patients after three to five years.  In patients who had a fairly long-lasting effect from their original trabeculoplasty, the procedure can be repeated once.  However, the drop in intraocular pressure the second time will not be as great as was seen initially.

P:  At what point do you consider using ALT for a patient?

Dr. Rick Wilson:  Usually, when the patient is on two or more medications or is having bad side effects.  The patient should also be older (say, older than 50 years) with good pigment in the drain and have the diagnosis of open-angle, pigmentary, pseudoexfoliative or normal-tension glaucoma.

P:  Can you predict whether or not laser surgery will be effective? 

Dr. Rick Wilson:  Yes, if the above conditions are met, then I can almost assure a 25 to 35% drop in IOP (intraocular pressure).

P:  What is the cause of elevated IOP in a patient who undergoes ALT?  I understand that can occur.    

Dr. Rick Wilson:  Inflammation causes a further blockage of the trabecular meshwork, along with swelling of the posterior trabecular meshwork from the burns, and a thicker fluid in the eye from the inflammation.

P:  Do dark irises need less laser energy?

Dr. Rick Wilson:  Yes, for a peripheral iridectomy.  The amount of power needed for an ALT is related to the amount of pigment in the trabecular meshwork.

P:  I live in England and face either laser or tube surgery, as soon as possible.  For a challenging case of  glaucoma and aniridia, what would be the benefit of laser over a tube?

Dr. Rick Wilson:  I assume that the laser you are talking about is a cyclophotocoagulation, where the laser is aimed through the wall of the eye and kills part of the part of the eye that makes the fluid.  If less fluid is made and less is getting out, perhaps a balance can be achieved with the use of medication.  The laser would be an outpatient procedure.  There would be no cutting, but it would entail a lot of inflammation and more pain, on average, than a tube.  It is usually somewhat more dangerous than a tube in most circumstances.

P:  Does the laser itself cause the inflammation, which then raises the IOP?

Dr. Rick Wilson:  Yes.

P:  I have secondary glaucoma in one eye due to trauma many years ago.  Why can't laser be used on the part of the trabecular meshwork that was damaged to open the undamaged parts and clear the drain? 

Dr. Rick Wilson:  I would think that the proportion of trabecular meshwork injured is too great.  There is not enough healthy meshwork to work with.

P:  Is a third laser treatment ever considered? 

Dr. Rick Wilson:  Not with an argon laser. 

P:  Is it true that it can take up to a month for the full effect to occur?

Dr. Rick Wilson:  Yes.

P:  What is plateau iris?  

Dr. Rick Wilson:  Plateau iris is a type of angle closure that can cause glaucoma.  The central anterior chamber of the eye is plenty deep, but the iris just in from the sclera is pushed forward and is close to, or blocks, the posterior trabecular meshwork. 

End of highlights for October 2, 2002.

On October 9, Dr. Wilson discussed "Cataracts and the Glaucoma Patient" in the Chat room. Click here for highlights of that meeting.

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