EyeWorld Asia-Pacific June 2018 issue

61 EWAP DEVICES June 2018 in 30 adult patients with POAG or PXFG. The investigators found transscleral SLT, without the use of a gonioscopy lens, to be a safer technique than SLT, with a thera- peutic potential comparable to that of the conventional method. 1 SLT was delivered to the study group without a gonioscopy lens, while a control group received conventional SLT therapy that involved 100 laser spots delivered for 360 degrees of the trabecu- lar meshwork. The study group underwent irradiation using the same parameters with the laser applications administered on the perilimbal sclera. Outcomes revealed similar IOP reductions between study group patients and controls of roughly 20%. Success was defined as a decrease in IOP of at least 15% at 6 months following the treatment, with no additional medications, laser, or glaucoma surgery. This was achieved in 12 (85.7%) study patients and nine (69.2%) controls (p=0.385). Com- plications were mild and transient in the study group, although significantly higher in controls (p<0.0001) and included anterior chamber inflammation and super- ficial punctate keratitis. The authors proposed that laser coherency, lost in tissue transmission, was not required to achieve the therapeutic effect, and that the mechanism of action of external irradiation was similar to that of conventional SLT. They concluded that gonioscopy was therefore not necessary for laser energy delivery in SLT. 2 While the study’s outcomes support the transscleral approach, not much else is known about the actual ef- fect of the laser on the eye or the required dose for efficacy. “The ultimate mechanism of SLT is still not completely elucidated,” Dr. Tai said. “Whether it is necessary for the laser to be aimed directly on the trabecular meshwork or not is not known. In fact, if transscleral SLT is effective, targeting the tra- becular meshwork precisely may not be important.” Huge potential A further implication of success with this technique is its potential to broaden the glaucoma treat- ment spectrum. “Traditionally, we have been taught that laser is for patients with an open angle; the more pigment on the trabecular meshwork, the better,” Dr. Tai said. “Is this true? With transscleral SLT, we may now have the option of treating patients with corneal opacities, closed angles, or other scenarios. How might transscle- ral SLT change current practice patterns? The traditional applica- tion of the laser is through the anterior chamber; by nature, this necessitates the patient having an open angle in order for the laser to reach the trabecular meshwork. If this method is successful, it can target a wider range of patients than traditional SLT, including patients with corneal opacities or peripheral anterior synechiae. I do not perform transscleral SLT, but the idea of it is appealing. Trans- scleral SLT will allow us to use this laser modality in a wider range of patients. It will also prompt us to study further the mechanism of the SLT laser in lowering intraocu- lar pressures.” According to Dr. Tai, the optimal laser settings for trabecu- loplasty are likely to vary per pa- tient, just as the energy it takes for bubble formation is different per eye. Although some studies have shown increased efficacy with higher amounts of laser power, she thinks that the concern is for a higher chance of adverse effects, such as intraocular pressure spikes, anterior chamber cell damage, and corneal edema, with higher energy application to the eye. Dr. Tai also performs micro- pulse laser trabeculoplasty and pattern scanning laser trabeculo- plasty. Micropulse laser trabecu- loplasty provides her with an effective laser modality to achieve similar results as with SLT, with re- spect to repeatability and the abil- ity to decrease intraocular pres- sure, with less inflammation noted postoperatively. Pattern scanning laser trabeculoplasty can decrease the time it takes for the procedure, as well as provide better “aim” at the trabecular meshwork, which can potentially increase efficacy and decrease adverse effects, she observed. “The reasoning here is that we may not need the goniolens to get the laser energy into the eye,” Dr. Radcliffe said. “The laser used in SLT can penetrate deeply into the eye and into Schlemm’s canal and the trabecular meshwork from the outside, meaning through the sclera. So transscleral SLT is exciting because it is a simpli- fied, faster, version of SLT with fewer side effects. But it has to be stated that we only have data on the 30 patients that were treated with transscleral SLT in the Gef- fen study, not data on hundreds or thousands of patients like we have for SLT. It may be that it is not effective in a larger patient set. It may be that its effect does not last as long. While we haven’t seen any evidence of it, it’s always pos- sible there is some new side effect related to this type of treatment that we are unaware of. However, based on SLT, of which there are easily a million patients treated and which is exceptionally safe, transscleral SLT represents a major step forward.” EWAP References 1. Geffen N, et al. Transscleral selective laser trabeculoplasty without a gonioscopy lens. J Glaucoma . 2017;26:201–207. 2. Belkin M, et al. Direct trans-scleral se- lective laser trabeculoplasty (SLT) without a gonioscopy lens. Invest Ophthalmol Vis Sci . 2014;55. Editors’ note: Drs. Radcliffe and Tai have no financial interests related to their comments. Contact information Radcliffe: drradcliffe@gmail.com Tai: Taniatai@gmail.com