Computer-guided treatment delivery builds on benefits of SLT

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Pattern scanning laser trabeculoplasty uses computer guidance for precise delivery of laser spots to the trabecular meshwork. At 6 months post-treatment, percentage IOP reduction was similar in eyes undergoing PSLT performed with a 577-nm laser compared with selective laser trabeculoplasty using a 532-nm laser.

By Cheryl Guttman Krader; Reviewed by Kaweh Mansouri, MD, and Miho Nozaki, MD, PhD

Results of a retrospective chart review based on 6 months of follow-up demonstrate that pattern scanning laser trabeculoplasty (PSLT) performed with a 577-nm laser (PASCAL Streamline 577, Topcon Medical Laser Systems) and computer-guided scanning technology is as effective as selective laser trabeculoplasty (SLT) for reducing IOP in patients with open-angle glaucoma, according to Miho Nozaki, MD, PhD.

“Like SLT, PSLT minimizes thermal injury to the trabecular meshwork, but with the computer-guided spot delivery, PSLT assures complete treatment without overlap or gaps,” said Dr. Nozaki, associate professor of ophthalmology and visual science, Nagoya City University Graduate School of Medical Sciences, Japan. “It was initially developed using a 532-nm laser (PASCAL streamline, Topcon Medical Laser Systems), and more recently, the scanning software became available for the yellow wavelength, 577-nm laser.

“The results of this retrospective review support the efficacy of PSLT with the 577-nm laser,” Dr. Nozaki said. “Now, a larger prospective, controlled study is required to verify the extent and durability of the IOP reduction.”

In PSLT, the computer-guided scanning technology sequentially delivers the treatment pattern onto the trabecular meshwork. After delivering a set of spots, the aiming beam automatically rotates so that the next pattern of spots is precisely aligned and applied onto an untreated location.

The retrospective study included 24 eyes of 21 patients. There were 12 eyes each in the PSLT and SLT groups and no significant differences between groups in demographic characteristics. The majority of patients in both groups had primary open-angle glaucoma. The PSLT and SLT groups were also similar in their mean baseline IOP (21.8 and 23.8 mm Hg, respectively) and mean number of medications used daily (2.7 and 3.1, respectively).

SLT was performed with a 532-nm laser (Tango Ophthalmic Laser, Ellex). All eyes were treated for 360°. In the PSLT group, the average number of spots delivered was 1277 and the average exposure energy was 1.7 mJ. In the SLT group, the average number of spots delivered was 88 and the average exposure energy was 0.8 mJ.

At 6 months, mean IOP was reduced to 14.3 mm Hg (-33%) in the PSLT group and to 17.3 mm Hg (-21%) in the SLT group; the difference between groups in percentage of IOP reduction was not statistically significant. There were also no significant differences between the PSLT and SLT groups at 6 months in mean medication use or the cumulative survival rate, although at 7 months, 3 SLT-treated eyes underwent additional glaucoma surgery.

One eye in each group developed a transient IOP elevation (>5 mm Hg). No eyes developed peripheral anterior synechia or showed corneal endothelial cell loss.

PSLT versus SLT

Kaweh Mansouri, MD, consultant ophthalmologist, Department of Ophthalmology, University of Geneva, Switzerland, and adjoint associate professor of ophthalmology, University of Colorado School of Medicine, Aurora, is currently conducting a randomized trial comparing PSLT and SLT. The study is enrolling patients with bilateral open-angle glaucoma who will be randomly assigned to receive PSLT or SLT in one eye and the alternate intervention contralaterally.

“Data available so far show that both PSLT and SLT reduce IOP by about 25% to 30%. Based on the magnitude of response, I refer to their benefit as a ‘laser prostaglandin effect.’ Since the computer-guided treatment mode ensures complete and regular treatment of the entire trabecular meshwork, PSLT theoretically may provide better outcomes than SLT in terms of greater IOP lowering and/or better long-term control,” he said.

“That remains to be seen, but our study is designed so that each patient serves as his or her own control and will enroll enough patients so that it will have sufficient power to detect any difference in treatment efficacy,” he said.

Dr. Mansouri’s study is also investigating patient comfort during treatment using visual analogue scale ratings. He noted that the data collected so far indicate that when it comes to tolerability, patients clearly prefer PSLT to SLT. Dr. Mansouri added there is also a need for data on re-treatment with PSLT.

Kaweh Mansouri, MD

E: kawehm@yahoo.com

Miho Nozaki, MD, PhD

E: miho.nozaki@gmail.com

Neither Dr. Nozaki nor Dr. Mansouri has any relevant financial interest to disclose.