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Selective laser trabeculoplasty is a safe and effective first-line procedure for glaucoma that works as well as the strongest anti-glaucoma medication.
SLT picked up where argon laser trabeculoplasty (ALT) left off-the major advantage of SLT is the dramatic reduction in energy used, with SLT using 6,000 times less energy than ALT. The procedure also lives up to its name. That is, it is selective in that it targets only the cells containing melanin, which results in less damage to adjacent cells, and the results are long lasting, Dr. Condon added.
"SLT is a big step forward," said Dr. Condon, clinical associate professor of ophthalmology, Drexel University College of Medicine; chairman, Department of Ophthalmology, and director, Glaucoma Division, Allegheny General Hospital, Pittsburgh.
Shlomo Melamed, MD, and colleagues performed a study in 2003 in which they used SLT as the primary therapy in a small series of eyes and found that mean IOP decreased by 30% (a mean of 7.7 mm Hg) from 25.5 to 17.9 mm Hg over the 1-year follow-up period.
The investigators concluded that "SLT is effective and safe as a primary treatment for patients with ocular hypertension and open-angle glaucoma." About 88% of these patients had a decrease in IOP of 5 mm Hg or more.
The SLT/Medication Study, a U.S./Canadian prospective randomized clinical study, compared SLT with topical medical therapy. The study was conducted at 17 sites and included 72 patients randomly assigned to either 360° SLT or 180° SLT (group 1) or prostaglandin analogue agents (group 2) as primary monotherapy. The interim results from 94 eyes followed for at least 8 months indicated that SLT therapy resulted in an IOP reduction that was equivalent to that with latanoprost (Xalatan, Pfizer) (31% versus 30.8%, respectively).
The Canadian Study conducted in London, Ontario, was a prospective multicenter trial of the safety and efficacy of SLT as initial therapy for open-angle glaucoma compared with latanoprost initial therapy. One hundred eyes of 61 patients were included. SLT reduced the IOP by 31%. At least 80% of both groups had a 20% reduction in IOP, and about 50% of both groups had a 30% decrease, Dr. Condon said.
He added that a new contender is micropulse laser trabeculoplasty, which is characterized by interruption of the laser effect, during which the tissue cools; 300-µs pulses alternate with 1,700-µs rests. This technology minimizes the thermal effect but does not completely eliminate it. Minimal study data are available to reach definitive conclusions about this technology, he explained.
Who responds to SLT?
Ike K. Ahmed, MD, evaluated SLT based on the type of glaucoma. He found in a study of 796 patients that the efficacy of SLT varied by glaucoma type. Patients with primary open-angle glaucoma had a mean IOP reduction of 24%; pseudoexfoliation glaucoma, 28%; pigmentary dispersion glaucoma, 28%; and mixed glaucoma, 29.4%. The response rates ranged from 73.7% to 90.3%.
"This is very positive information about the effect of SLT," Dr. Condon said.
Realistically, he said, SLT would be a feasible first-line therapy for patients with open-angle glaucoma and moderate IOP elevations but not for patients with uveitis or low-tension glaucoma.
"Sensible patient selection is needed for SLT as the first-line therapy," he said. "The reasonable candidates are those who should have an IOP in the teens and 20s with mild to moderate disease who are not in a crisis with advanced disease or out of control despite maximal medications."
Dr. Condon said that he likes to perform SLT early in the treatment plan in order to achieve the greatest treatment effect. Most other physicians, however, seem resistant to performing SLT as the first-line therapy and only resort to SLT when the first-line medication does not achieve the desired effect, he explained.
In his hands, more than 70% of his patients usually have a 4 to 8 mm Hg decrease in IOL. The higher the baseline IOL, the greater has been the reduction. The final treatment effect is apparent 6 to 8 weeks after treatment. Importantly, there is a high risk of an IOP spike in patients with pigmentary glaucoma.
The burning question
SLT re-treatment, defined as re-treating the trabecular meshwork that was treated previously, seems to be controversial. "But why might it work?" Dr. Condon asked.
"We believe that the SLT tissue reaction is chemically mediated and uses the immune system to clean the meshwork," he said. "The response with ALT is by thermal tissue destruction. The same chemical pathway might be involved to some degree. Mechanical factors and damage that are permanent also are involved in ALT, which limits the potential for re-treatment."
In support of re-treatment, Hong and co-workers recently reported the effect of 360° re-treatment of 44 eyes. The authors concluded that 360° SLT can be repeated at least 6 months after successful 360° SLT with similar good IOP reductions.
"SLT is safe and effective as a first-line therapy and has greater treatment potential," Dr. Condon concluded. "It reduces IOP with more patient comfort and less tissue damage."
Garry P. Condon, MD
Dr. Condon has no financial interest in the subject matter.