Eyeworld

EW GLAUCOMA 36 by Tony Realini, M.D. Energy settings in SLT: how much is enough? S ince its introduction in 2001, selective laser tra- beculoplasty (SLT) has sig- nificantly altered the traditional stepped treat- ment regimen for glaucoma man- agement. Once reserved for eyes failing maximal medical therapy, trabeculoplasty is now offered signif- icantly earlier in the treatment para- digm, 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 trabeculo- plasty (ALT). It is true that SLT uti- lizes 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 signifi- cant differences between the two laser platforms do not appear to af- fect the efficacy and safety of tra- beculoplasty, which have been shown in numerous studies to be equivalent for SLT and ALT. However, a pair of studies pre- sented at the 2010 annual meeting of the Association for Research in Vi- sion and Ophthalmology (ARVO) suggests that energy settings do mat- ter when performing SLT. In fact, higher energy settings may produce greater IOP reductions. High energy boosts SLT success Douglas Rhee, M.D., Boston, pre- sented the results of a study con- ducted at the Massachusetts Eye and Ear Infirmary designed to identify predictors of successful IOP reduc- tion 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 fel- low eye." To test their hypothesis, Dr. Rhee and his team reviewed the medical records from all patients un- dergoing bilateral SLT between 2002 and 2008. They identified 89 pa- tients who underwent SLT after being deemed poorly controlled on maximal medical therapy and were followed for a minimum of six months post-laser. The group de- fined SLT success as an IOP reduc- tion of 3 mm Hg or more at last follow-up without the need for fur- ther IOP-lowering interventions. They observed that the SLT out- come 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 pre- dictor than failure. With a mean of 13 months between fellow eye treat- ments, 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 pa- tients 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 summa- rized, "the chance of success in the contralateral eye is low. Based on our results, higher energy may be help- ful to obtain better outcomes when applying SLT to the contralateral eye." High energy improves IOP response The optimal settings for SLT treat- ment have not been completely characterized. Currently, most clini- cians titrate the energy setting until they see a tiny burst of so-called champagne bubbles emerge from the angle after each laser applica- tion. Albert Khouri, M.D., New Jer- sey Medical School, Newark, exam- ined the effect of high versus low energy settings on the magnitude of IOP reduction seen after SLT. "We compared the IOP out- comes in two groups of patients," Dr. Khouri said. "One group under- went SLT at the traditional energy settings, in which energy was titrated to the appearance of cham- pagne bubbles. The mean energy level per treatment spot was 0.8 mJ. The other group underwent SLT at uniformly higher energy levels, gen- erally around 1.5 mJ per spot." This was a retrospective chart re- view, Dr. Khouri said. He explained that the data came from the patients of two clinicians, one who consis- tently used traditional settings on all patients and one who consistently used high energy settings on all pa- tients. "At one month, four months, and eight months following SLT, the mean IOP reduction was consis- tently and statistically significantly lower in the eyes undergoing high- energy SLT compared to conven- tional SLT," he said. Mean IOP reductions at one, four, and eight months were 3.6 mm Hg, 3.2 mm Hg, and 3.0 mm Hg, re- spectively, in the conventional group, versus 4.9 mm Hg, 4.6 mm Hg, and 5.8 mm Hg, respectively, in the high-energy group. At each fol- low-up time point, the p-value for the difference was below 0.05, he said. New questions While the results of this study are encouraging, Dr. Khouri cautioned against widespread adoption of high energy SLT at this time. "These data raise some interest- ing questions," Dr. Khouri said. "Higher energy may provide greater IOP reduction, but is it as safe as SLT at conventional energy settings?" He also mentioned that at least one published report has demon- strated that SLT can be safely and ef- fectively repeated once its effect wears off. "We also have to ask whether high energy SLT is as re- peatable as SLT performed at con- ventional energy levels." EW Contact information Khouri: albertkhouri@hotmail.com Rhee: dougrhee@aol.com January 2011 Both ALT and SLT impact the trabecular meshwork; however SLT seems to allow repetitve treatments Source: Alan Robin, M.D. Comparison of SLT vs ALT SLT ALT Ratio 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

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