SLT, ALT comparable in ability to lower IOP, research finds

January 15, 2008

Selective laser trabeculoplasty (SLT) is comparable with argon laser trabeculoplasty (ALT) in its ability to lower IOP in patients with open-angle glaucoma, according to 5-year results of a randomized, controlled trial from the University of Ottawa reported at the American Academy of Ophthalmology annual meeting.

Key Points

Dr. Damji, associate professor of ophthalmology, University of Ottawa, cautioned that the population that he and his colleagues studied in their randomized, controlled clinical trial was treated with maximal-tolerated medical therapy and then received laser treatment. "So one can't extrapolate right away to anybody who has early glaucoma," he said.

SLT is performed with a Q-switched, 532-nm, melanosome-specific Nd:YAG laser, Dr. Damji explained. "The short pulse duration of 3 nanoseconds is what gives it, through selective photothermolysis, that exquisite selectivity so that heat energy does not dissipate beyond the cells that are affected."

Study details

The study included patients with primary open-angle pseudoexfoliation and pigmentary glaucoma in whom IOP was uncontrolled (greater than 16 mm Hg) after maximum medical treatment or 180° or 360° ALT (performed at least 6 months prior to enrollment). Patients were excluded if they had a visual field defect within 10° of fixation, if they previously had undergone glaucoma surgery other than ALT or peripheral iridotomy, if they had corneal disease that could render applanation tonometry inaccurate or could hinder the visualization of the trabecular meshwork, or if they used systemic or topical steroids.

Eyes were assigned randomly to be treated with ALT or SLT. The ALT group contained 87 eyes, and the SLT group had 89 eyes. The average age (about 70 years), gender, and baseline IOP (about 24 mm Hg) of patients in each group were similar. Best-corrected visual acuity differed slightly in each group (20/40 in the ALT group versus 20/30 in the SLT group), as did the number of eyes that had undergone previous ALT (39 in the ALT group versus 27 in the SLT group).

Mean trabecular meshwork pigmentation was 2.3 in the ALT group and 2.4 in the SLT group on a scale of 0 to 4+ in which 0 represented no pigmentation and 4+ represented dark, mascara-like pigment. The number of medications taken for glaucoma averaged 2.4 in the ALT group and 2.6 in the SLT group. Pseudophakic patients made up about one-third of each group.

Laser treatment generally was performed to the inferior 180° of the trabecular meshwork. If ALT previously had been performed in this area, however, the superior portion of the trabecular meshwork was treated.

In this trial, ALT was performed using 50 applications, a 50-µm spot size, a 0.1-second pulse duration, and an average power of 550 mW (range, 300 to 1,300 mW). SLT was performed using a specific model of laser (Selecta 7000, Lumenis), 50 applications, a 400-µm spot size, a 3-nanosecond pulse duration, and average energy of 0.8 mJ (range, 0.47 to 1.5 mJ). All eyes were pre-treated with apraclonidine (Iopidine, Alcon Laboratories) or brimonidine tartrate 0.2% (Alphagan, Allergan) and received topical steroids for 5 days postoperatively.

5-year results

Five-year follow-up included 64 patients (72%) in the SLT group and 56 patients (64%) in the ALT group.

"If we look at the pressure over time, there clearly was a drop of about 25% initially [from preoperative levels to 1-year levels], and this [decrease] was sustained over time if you just look at the total numbers. This is true in both groups," Dr. Damji said (Figure 1).