Complications Accompanying Lasers
Chat Highlights
February 8, 2006

On Wednesday, February 8, 2006, Dr. Rick Wilson, a glaucoma specialist at Wills, and the glaucoma chat group discussed "Complications Accompanying Lasers."

Moderator:  Good evening, Dr. Wilson.  Tonight the topic is "Complications Accompanying Lasers.”  What kinds of lasers do you use in your practice?

Dr. Rick Wilson:  I use an argon, a selective, a krypton (sorry, Superman) or dye laser, and a neodymium YAG (Nd:YAG) laser.

Moderator:  How do you use those lasers?

Dr. Rick Wilson:  I use the argon laser to cut sutures after trabeculectomy, the selective laser for trabeculoplasty, the krypton (a red laser) to cut sutures if there has been any bleeding under the conjunctiva, and the YAG for iridectomies.

Moderator:  Are some lasers safer than others?

Dr. Rick Wilson:  The selective laser seems to be the safest, but post-operative pressure rises do occur.

P:  What type of laser is used to clear a cloudy lens?

Dr. Rick Wilson:  A Nd:YAG laser is used to open a cloudy "secondary cataract," a clouding of the capsule behind the intraocular lens.

P:  What complications could occur when a patient with uveitis who has had a trabeculectomy has that procedure?

Dr. Rick Wilson:  Clouding would be much more common in a patient with uveitis.  Because of the extra inflammation in the eye, swelling in the back of the eye can occur.

P:  Are there more or fewer complications with laser trabeculotomies or with surgical trabeculectomies?

Dr. Rick Wilson:  Complications following trabeculotomy are fewer and usually less severe, although I have also seen corneas lost and flat chambers from lasers.

P:  What causes the loss of the corneas?

Dr. Rick Wilson:  If too much energy, especially in the form of heat, is released in the anterior chamber, it can cook the lining of the cornea, causing the cornea to turn white.

P:  What would cause the chamber to flatten?

Dr. Rick Wilson:  If a laser panretinal photocoagulation for diabetic retinopathy is too intense, it can cause the choroid to swell, pushing the iris forward into the trabecular meshwork.

P:  Are there differences in the complications from laser trabeculoplasty and iridectomy?

Dr. Rick Wilson:  Yes.  The most common complications from an iridectomy are bleeding and injury to the cornea or lens.  The most common complication from a trabeculoplasty is a spike in intraocular pressure, although inflammation and a red eye can linger in some patients.

P:  What are "bleeds" and how are they treated?

Dr. Rick Wilson:  A vessel in the iris can be cut as the laser blasts its way through the iris, causing bleeding.  Pressure on the lens used to focus the laser will raise the IOP (intraocular pressure) high enough to stop the bleeding.

P:  I didn't know that an iris could bleed.  My iris is pulled from ICE syndrome, but that type of damage wouldn't cause it to bleed, would it?

Dr. Rick Wilson:  The membrane on your iris pulling it apart seems to damage the blood supply, so there are melting holes in the iris where the tissue doesn't get blood flow and just melts away.  In other areas, the tissue is pulled apart by the membrane.  Bleeding is never a problem unless the iris is cut.

P:  What is an iridectomy?  Does it fix the problem permanently?

Dr. Rick Wilson:  During an iridectomy, a small hole is cut in the iris. In most patients with narrow angles, it does fix the problem.  If there has been pre-existing angle closure, the iridectomy may not open the angle.  A small percentage of patients with plateau iris will not be helped enough to avoid angle closure.

P:  I had terrible pain after one of my many lasers. Is severe pain unusual?

Dr. Rick Wilson:  Yes, although some eyes, especially those that have already gone through a lot, are more sensitive.

P:  What is the main reason SLT fails?

Dr. Rick Wilson:  The main reason is a patient who lacks the best characteristics to do well. Success with the laser is directly related to the age of the patient and the right diagnosis. The older the patient, the better.

The right diagnosis includes pseudoexfoliative (PSXF), pigmentary, primary open-angle, and normal-tension glaucoma.  There also needs to be enough pigment in the trabecular meshwork to absorb the laser energy.  I see many patients these days who have had a laser that didn't work.  That could have been predicted easily before the laser surgery.

P:  Are you using SLT exclusively for trabeculoplasty?

Dr. Rick Wilson:  Almost exclusively, because we have an SLT. Until it is proven that an SLT can be repeated multiple times, there is little impetus for a doctor to buy an SLT.

P:  Nevertheless, judging from the number of glaucoma patients in our chat group who have had a trabeculectomy, SLT now seems to be performed more often than ALT.

Dr. Rick Wilson:  I think that is true.  It's the new thing, one that I hope is significantly better, but can't be sure.

P:  Are there differences in the number of complications between ALT and SLT?

Dr. Rick Wilson:  Yes.  The SLT is a more benign procedure, although a judicious low- energy ALT and a SLT will have very similar complications.  The effects of SLT on the eye are invisible, whereas the burns from ALT can often be seen during high magnification viewing of the trabecular meshwork.

P:  What adverse event or condition would preclude repetition of SLT?

Dr. Rick Wilson:  If the SLT was done well the first time and didn't work satisfactorily, there would be little use to repeat it.

P:  I was told that if there isn't a lot of pigment in the trabecular meshwork, SLT could still be done by changing the frequency of the laser.  Did I misunderstand something?

Dr. Rick Wilson:  The SLT is a frequency- doubled YAG, set at a standard frequency. It cannot be changed.  What you may have heard concerns one study suggesting that SLT might not need as much pigment as ALT to be effective.  It was not a strong study.

P:  I had a shower of black spots after I had laser to clear a cloudy implant. What were those spots?

Dr. Rick Wilson:  Those were probably small pieces of the cloudy capsule that was cut open. They float around in the vitreous jelly until they finally sink out of your vision.

P:  Are floaters common after lasers?

Dr. Rick Wilson:  Only after capsulotomies.

P:  Does the SLT work well on blue-eyed people?

Dr. Rick Wilson:  The color of the iris means little.  It is the amount of pigment caught in the trabecular meshwork that enables the energy of the laser (Light Amplification through Stimulated Emission of Radiation) to be absorbed.

P:  Can laser sometimes cause persistent blurred vision?

Dr. Rick Wilson:  If the laser hit the retina or caused corneal injury or a serious intraocular inflammation, the laser could cause persistent blurred vision.

P:  If a trabeculectomy is not working as well as hoped, can laser (trabeculotomy) be tried?

Dr. Rick Wilson:  Occasionally, a membrane covering the inner opening of the trabeculectomy drain can be opened with the laser.

P:  Can a nerve be hit as the laser cuts through the iris?

Dr. Rick Wilson:  Probably, but I've never known it to be a problem.

P:  How common is plateau iris syndrome?

Dr. Rick Wilson:  Plateau iris syndrome is uncommon; perhaps 3% of all cases of angle-closure glaucoma.

P:  How many times can iridoplasty be repeated safely in a case of narrow-angle glaucoma and plateau iris syndrome?

Dr. Rick Wilson:  I have performed iridoplasty on many patients three times, but not more.  Usually, by that time, the cataract is ready to be removed. Removal of the cataract results in more room in the front of the eye.

P:  I've seen comparative images showing trabecular meshwork (TM) following ALT and SLT procedures.  In the ALT images, the TM is very tangled, like a plate of spaghetti.  In the SLT images, the TM looks neater, with clear holes punched through it.  Why is the appearance different?

Dr. Rick Wilson:  Both lasers seem to stimulate the cells lining the meshwork to divide.  The new cells formed are much more active, eating the debris that builds up in the meshwork and getting rid of it.  The argon causes a small burn; the effect of the SLT cannot be seen with just light microscopy.

P:  What happens to the meshwork in ALT and SLT to cause the loss of effectiveness?

Dr. Rick Wilson:  The debris that caused the original glaucoma keeps coming and finally causes the effect of the laser to ebb.

Moderator:  Thanks for a great chat, Dr. Wilson.

On February 15, Dr. Henderer discussed "Disc Damage Likelihood Scale" in the Chat room. Click here for highlights of that meeting.

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