EyeWorld Asia-Pacific June 2011 Issue

40 EW GLAUCOMA June 2011 Both ALT and SLT impact the trabecular meshwork; however, SLT seems to allow repetitive treatments Source: Alan Robin, MD Energy settings in SLT: how much is enough by Tony Realini, MD SLT is generally considered kinder and gentler to ocular tissue; now surgeons are considering ramping up their energy settings to achieve greater IOP reductions S ince its introduction in 2001, selective laser trabeculoplasty (SLT) has significantly altered the traditional stepped treatment regimen for glaucoma management. Once reserved for eyes failing maximal medical therapy, trabeculoplasty is now offered significantly earlier in the treatment paradigm, often even as primary therapy. One likely explanation for this evolution is the general belief that SLT is kinder and gentler to ocular tissues than argon laser trabeculoplasty (ALT). It is true that SLT utilizes far lower energy settings than ALT, and histologic studies have confirmed that SLT produces far less tissue damage to the trabecular meshwork than ALT. These significant differences between the two laser platforms do not appear to affect the efficacy and safety of trabeculoplasty, which have been shown in numerous studies to be equivalent for SLT and ALT. However, a pair of studies presented at the 2010 annual meeting of the Association for Research in Vision and Ophthalmology (ARVO) suggests that energy settings do matter when performing SLT. In fact, higher energy settings may produce greater IOP reductions. High energy boosts SLT success Douglas Rhee, MD, Boston, Mass., USA, presented the results of a study conducted at the Massachusetts Eye and Ear Infirmary designed to identify predictors of successful IOP reduction following SLT. “SLT is an effective method to treat open-angle glaucoma, and many patients may require SLT in both eyes,” Dr. Rhee said. “Little is known about predictive factors for SLT success. We hypothesize that the outcome of SLT in one eye will be predictive of the outcome in the fellow eye.” To test their hypothesis, Dr. Rhee and his team reviewed the medical records from all patients undergoing bilateral SLT between 2002 and 2008. They identified 89 patients who underwent SLT after being deemed poorly controlled on maximal medical therapy and were followed for a minimum of SLT ALT Ration No. of Spots 50 50 Energy 0.8-1.4 mJ 400-600mw 1:100 Fluence (mj/mm2) 6 40,000 1:6000 Exposure Time 3 nsec 0.1 sec Comparison of SLT vs ALT six months post-laser. The group defined SLT success as an IOP reduction of 3 mm Hg or more at last follow-up without the need for further IOP-lowering interventions. They observed that the SLT outcome in the second-treated eye was identical to that in the first- treated eye 75% of the time. Success in the first eye appeared to be a better predictor than failure. With a mean of 13 months between fellow eye treatments, first eye success led to second eye success in 88% of patients, while first eye failure led to second eye failure in 71% of patients. Interestingly, among the 22 patients with disparate results between the two eyes, the major predictors of success were the number of pre-laser IOP medications used and the SLT energy level used for treatment. “If there is a poor response to SLT in one eye,” Dr. Rhee summarized, “the chance of success in the contralateral eye is low. Based on our results, higher energy may be helpful to obtain better outcomes when applying SLT to the contralateral eye.” High energy improves IOP response The optimal settings for SLT