Laser trabeculoplasty treatment by the letter
by Maxine Lipner Senior EyeWorld Contributing Editor
The latest on what to expect from varying laser trabeculoplasty options
It's often par for the course with open-angle glaucoma patients' use of laser trabeculoplasty. For patients it's a quick, pain-free option that may help to alleviate the need for drops. There's a whole alphabet soup of approaches —ALT (argon laser trabeculoplasty), SLT (selective laser trabeculoplasty), and MLT (micropulse laser trabeculoplasty). But of course not all laser trabeculoplasty is equal, or is it? Here's what EyeWorld found.
SLT vs. ALT
For some time, practitioners have been weighing how SLT, the relative newcomer, stacks up against the more traditional ALT, which has been around for decades. Paul L. Krawitz, M.D., assistant clinical professor of ophthalmology, Columbia University College of Physicians and Surgeons, New York, has used both treatments in his practice. While both supply energy to the trabecular meshwork, they work in different ways. "ALT is visible light that interacts with the pigment that's in the trabecular meshwork and actually causes a tiny burn," Dr. Krawitz said. "Selective laser trabeculoplasty, called a Q-switched YAG laser, applies energy that's invisible." Both apply energy to the trabecular meshwork, which filters aqueous and lowers pressure. "The difference functionally is that the argon laser, because it causes a small burn, physically destroys a small portion of the trabecular meshwork," Dr. Krawitz said.
While both are equally effective in studies, Dr. Krawitz sees a key difference between the two. "Argon laser trabeculoplasty, because it causes physical damage to the trabecular meshwork, can't be repeated ad infinitum, if the pressure starts rising in a couple of years," he said. With ALT, practitioners can actually witness the burn to the trabecular meshwork, which paradoxically is a sign that the argon spot has been successfully applied.
Dr. Krawitz finds that he can repeat the SLT procedure with his Lumenis laser (Santa Clara, Calif.) several times—something that completely changes the treatment algorithm as a result, in a disease that currently practitioners hope to control at best. "The issue with argon laser trabeculoplasty is that you run out of bullets," Dr. Krawitz said. "You can do it once and get a lot of mileage, the second time gets a little less mileage, and then you have to look for an alternative way of controlling pressure." Meanwhile, he finds that SLT can be redone. "Although on a first-time basis SLT has an equivalent result, you know that 2-4 years later, should the patient's pressure elevate again you can come back to tissue that has not been destroyed by heat burns and reapply energy," Dr. Krawitz said. "It puts a lot more bullets in your gun to maintain the patient's pressure."
Initial outcomes with ALT and SLT are roughly equivalent. "In the literature they both have about an 80% success rate at reducing pressure in a meaningful way," Dr. Krawitz said. In his hands, he finds that his numbers for ALT are about a 70-75% success rate and up to 88% for SLT. The pressure reduction is about 20%.
Adding MLT to the mix
Adam J. Lish, M.D., attending in ophthalmology, Mount Sinai Medical Center, New York University, New York, has in the past used ALT. However, instead of turning to SLT when he needed a new laser, he opted for MLT with the IQ 810 (Iridex Corp., Mountain View, Calif.). "As a glaucoma specialist I was looking for a laser to replace my argon laser," Dr. Lish said. "My interest in diode lasers started when I was a fellow back in the early 90s, and I was well aware that diode did the job; also, my retina specialist used an iris diode laser to do his work."
That led Dr. Lish to MLT, which makes use of the diode technology. "It does as good a job clinically as ALT and SLT and does not cause scarring like ALT," Dr. Lish said. One of the other things that drew him to the MLT laser was the fact that, unlike SLT, it could do a variety of things. "Even in a glaucoma specialty office there are other things that you need to do with the laser," Dr. Lish said. In addition to trabeculoplasty, he found that the MLT laser could do iridoplasty, cut sutures, and perform laser iridectomy. He also felt that it was more financially responsible since the laser cost about 40% less than an SLT laser and could serve a variety of purposes.
Outcomes with MLT are equivalent to ALT, Dr. Lish finds. There was no scarring involved with the technique.
With MLT technology the diode laser emits a train of short pulses instead of one continuous one, according to Giorgio Dorin, Ph.D., director of clinical application and development, Iridex. With these short pulses, the tissue has a chance to cool between shots, and the thermal response is confined around the absorbing melanosomes.
The mechanism of action for laser trabeculoplasty is the same for all lasers, Dr. Dorin thinks. He pointed out that all have comparable IOP reduction in the 20-25% range. Dr. Dorin believes that the real contribution in trabeculoplasty is cellular renovation that can actually transport ocular fluid inside the cell and regulate this in such a way that the pressure in the eye decreases. "This type of cellular renovation occurs in every type of trabeculoplasty—it's a stress response," Dr. Dorin said. "You induce stress and then you have a response." He pointed out that Mother Nature is pretty good at repairing when there is something that could be repaired.
With laser trabeculoplasty, scarring is the watchword, Dr. Lish thinks. "Just like any laser trabeculoplasty, the thing that you have to realize about laser trabeculoplasty is as long as you're not causing scarring, it doesn't matter what laser you use," he said. "It doesn't matter if it lowers pressure."
When it comes to repeatability of laser trabeculectomy, he stressed that it's important to make sure that you're comparing apples to apples. He pointed out that with ALT the standard was to do 180 degrees and then come back later and do the rest. "The jury is still out on MLT as to what's best, 180 degrees or 360 degrees, and what constitutes one treatment," Dr. Lish said. At this point, he stressed that there is not one data set that can show repeatability for any of the laser trabeculoplasty procedures beyond the initial 360 degrees. Overall, Dr. Krawitz finds that his patients are thrilled with the SLT option. "Patients who had never complained about the irritation, the cost, the pigmentation, and the redness that they were getting on drops would come back 4-6 weeks after their SLT and be giddy with happiness at being off the drops," he said. "For us that has solidified our choice to heartily recommend SLT."
Meanwhile, Dr. Lish urged practitioners to ask critical questions when choosing a laser trabeculoplasty approach. "There is not one right answer for every practice, but for my practice, MLT was a good answer that I'm pleased with," he said.
Editors' note: Drs. Dorin and Lish have financial interests with Iridex. Dr. Krawitz has no financial interests related to his comments.
Contact information
Dolin: gdorin@iridex.com
Krawitz: krawitzmail-2@yahoo.com
Lish: ajlishmd@gmail.com
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