Retrospective single-surgeon study suggests ALT superior to SLT

Calgary, Alberta, Canada-In a single-surgeon study of glaucoma patients with uncontrolled IOP on maximally tolerated medical therapy, argon laser trabeculoplasty (ALT) was associated with a greater IOP-lowering effect than selective laser trabeculoplasty (SLT), reported Bryce Ford, MD.

The study included 108 consecutive patients treated with ALT between 1999 and 2002 and 108 patients consecutively treated with SLT between 2002 and 2004. Eligible patients were those with primary open-angle glaucoma (POAG), pseudoexfoliation glaucoma, or pigment dispersion glaucoma, although POAG was the predominant diagnosis.

Patients in the two groups had a similar mean age (68 years). However, compared with the SLT group, patients treated with ALT had a higher baseline mean IOP (19.8 versus 18.5 mm Hg) but were using fewer medications on average (2.02 versus 2.45). In addition, there were nearly three times as many pseudophakic patients in the SLT group compared with the ALT group (30% versus 11%).

"This retrospective study was undertaken to help us determine if by switching from ALT to SLT we were achieving better outcomes for our patients. It is possible that baseline differences in IOP between treatment groups may partially explain the superiority demonstrated for ALT. Clearly, further research including more patients with longer follow-up is required to determine if the trends found in this study will be validated," said Dr. Ford.

The study excluded patients who were undergoing repeat treatment with the same laser. However, some patients who underwent SLT had received previous ALT while none of the patients who underwent ALT had any previous laser treatment.

Treatment of 180°

A standard protocol was used for ALT involving 180° of treatment with a mean of 54 spots. SLT was performed with the Q-switched, frequency-doubled 532-nm Nd:YAG laser (Selecta 7000, Lumenis) and was also performed over 180° of the trabecular meshwork with a mean of 103 spots.

"The total number of spots delivered for SLT is relatively high. However, because this treatment only affects the pigment of the trabecular meshwork, this protocol was used to ensure coverage of the entire 180° area," Dr. Ford explained.

All patients were treated with apraclonidine 0.5% (Iopidine, Alcon Laboratories) pre- and post-treatment and also received prednisolone acetate 1% (Pred Forte, Allergan) four times a day for 5 days post-treatment.

"It is worth noting that there is some debate on whether a corticosteroid should be used after SLT considering that induction of an inflammatory response is thought to mediate the IOP-lowering effect of this treatment. Nevertheless, all patients received prednisolone acetate," he said.

To determine if there were any factors predicting response to SLT, the 108 patients who received that treatment were categorized as responders or non-responders. Then, those two subgroups were compared with respect to a number of demographic and disease-related characteristics.

With responders defined as patients with eyes that achieved an IOP reduction exceeding 2 mm Hg, the total series included 54 responders to SLT and 54 non-responders.

In multivariate analyses, baseline IOP was the only variable that differed significantly between the responders and non-responders, with the responders having a higher mean value than the non-responders, 19.3 versus 17.8 mm Hg.