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SLT, ALT excellent options for managing adult open-angle glaucomas
Laser trabeculoplasty procedures are safe and effective, with minimal complications, according to one specialist.
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Selective laser trabeculoplasty and argon laser trabeculoplasty offer a number of potential advantages compared with medical therapy and can also be used in conjunction with medical therapy. However, like all interventional treatments, there are potential risks that need to be considered when helping patients decide what is the right treatment, according to one surgeon.
Douglas J. Rhee, MD, described the benefits and risks associated with laser trabeculoplasty at the OSN New York Symposium and in a telephone interview with Ocular Surgery News. He said the most obvious advantage of laser trabeculoplasty over medical therapy is compliance. If the procedure can be performed once, and the patient has adequate pressure lowering that does not require further treatment, then patients will not have to continually take a dose of a medication, which can be difficult for some.
One other potential advantage is cost-savings with one laser trabeculoplasty treatment vs. chronic medication treatment. He said there are significant “if” factors required for the procedure to be cost-effective: if the laser trabeculoplasty adequately lowers IOP to a target pressure and if no additional medications are required.
With the advent of SLT, there was an increase in interest concerning laser trabeculoplasty, which brought the procedures to the forefront. They have been found to be safe and effective, with minimal complications, he said.
“It certainly has a role in managing adult open-angle glaucomas, refractory to medications,” Dr. Rhee said. “It can, certainly, be offered as primary treatment; however, just think before you shoot. There are significant concerns, both real and theoretical.”
How it works
Laser trabeculoplasty works by delivering laser energy to the trabecular meshwork. It enhances aqueous outflow. Dr. Rhee said different wavelengths have been attempted in the past, but ALT and the double-frequency Nd:YAG, or SLT, are now the two most commonly used. ALT was introduced in 1979, he said. It is a thermal laser that creates a burn in the trabecular meshwork.
 Douglas J. Rhee |
The selective double-frequency Nd:YAG laser works by targeting the melanin granules and ablating the pigmented trabecular meshwork cells selectively, he said.
“Both these lasers most likely work by increasing extracellular matrix turnover in the trabecular meshwork, using a family of enzymes called matrix metalloproteinase that chew up that matrix and allow there to be more drainage,” Dr. Rhee said.
He said there are a number of studies that show promising results for both procedures. For ALT, the Glaucoma Laser Treatment Trial looked at patients who were randomly assigned to one eye receiving ALT and the other eye receiving medications, starting with timolol. Of 271 patients, 44% had a pressure less than 21 mm Hg, the defined success criteria at 2 years, and 20% less than 21 mm Hg at 7 years. He noted that there was an issue with the study design of the trial because timolol had a small effect on the laser-treated eye.
For SLT, studies have shown that there is a 70% response rate, according to Dr. Rhee. At about 3 to 4 months’ postoperative, there is an average of 6 mm Hg of IOP lowering. SLT, as a primary treatment, is roughly equivalent to modern medications in short-term studies. With more time, longer-term data from these studies should be available.
Although ALT and SLT compare favorably with each other, they have some minor procedural differences when it comes to duration, spot size and energy. In a study by Mark Juzych, MD, 180° of ALT had equivalent success rates to 180° of SLT treatment after 5 years. Dr. Rhee told OSN he prefers to use one 360° SLT treatment.
One potential advantage of SLT over ALT is that it may be more effective when laser trabeculoplasty has already been performed once (ie, repeatability). However, this aspect needs further study. Dr. Rhee said if the IOP-lowering goal was not reached after performing SLT once, he would typically perform a surgical procedure.
“If the IOP goal is reached, but the IOP later drifts above the goal, I would consider repeating the SLT, if the IOP effect lasted more than 12 months,” Dr. Rhee said.
Complications
Dr. Rhee said potential complications are “fairly minimal” for SLT and ALT. The most immediate risk is a postop IOP spike, but rates are less than 1%. Peripheral anterior synechia are often seen with ALT, but they are usually clinically irrelevant. Also, there is an increased risk of bleb encapsulation. In addition, laser trabeculoplasty has a theoretical long-term risk of accelerating loss of the trabecular meshwork cells.
A key potential concern is an increased risk of failure for subsequent trabeculectomy, according to Dr. Rhee. Some research on the subject has shown that trabeculectomy after ALT has a higher failure rate. Other research, however, has found no increased risk.
“In general, ALT and SLT are effective and generally safe procedures. Laser trabeculoplasty can be offered as primary treatment, in lieu of adding medications, before a filtering procedure, or even after a trabeculectomy,” he said. “However, evaluate the evidence and think before you shoot.”
For more information:
- Douglas J. Rhee, MD, is an assistant professor of ophthalmology at Harvard Medical School and on the faculty of the Massachusetts Eye and Ear Infirmary. He can be reached at 243 Charles St., Boston, MA 02144; 617-573-3670; fax: 617-573-3707; e-mail: dougrhee@aol.com.
References:
- The Glaucoma Laser Trial Research Group. Results of argon laser trabeculoplasty versus topical medicines. The Glaucoma Laser Trial. Ophthalmology. 1990;97:1403-1413.
- Hattenhauer MG, Johnson DH, et al. Probability of filtration surgery in patients with open-angle glaucoma. Arch Ophthalmol. 1999;117:1211-1215.
- Erin L. Boyle is an OSN Staff Writer who covers all aspects of ophthalmology.