Eyeworld

EW FEATURE 46 Microinvasive glaucoma surgery (MIGS) • May 2016 Transscleral cyclophotocoagula- tion, which can now be performed with a micropulse laser, similarly reduces aqueous production. Dr. Radcliffe, who has performed more than 100 micropulse procedures over a 2-year period, said the mi- cropulse delivers energy in 0.5 µs doses, rapidly alternated with 1.1 µs rest over a 100-second period, rather than for 2 seconds continuously as the previous transscleral cyclophoto- coagulation technique. "While cyclophotocoagulation was traditionally reserved for more severe cases of glaucoma, we are now using micropulse earlier and earlier in the disease paradigm," he said. "In my practice, I have com- bined micropulse cyclophotocoagu- lation with cataract surgery and oth- er traditionally minimally invasive [procedures], although micropulse still presents risks." Dr. Tanaka said he has per- formed about 15 micropulse laser treatments and found that it can help avoid some complications associated with trabeculectomy and tube shunts and eliminates the risk of endophthalmitis because it is not an intraocular procedure. However, he noted the need for retreatment in many cases, its potential to cause loss of vision or accommodation in young, phakic eyes, as well as several unknowns such as risk for cataract progression, hypotony, and phthisis. Arthur Sit, MD, associate professor of ophthalmology, Mayo Clinic, Rochester, Minnesota, said that while stemming the production of aqueous humor might reduce IOP, it does not address the physiologi- cal problem of outflow resistance, which causes glaucoma, possibly leading to IOP fluctuation later down the road. Picking a procedure "With all of these options, how does one choose an approach to take?" Dr. Radcliffe asked. "While we do have some pub- lished data, we don't have well-con- trolled, head-to-head trials, so it may come down to the physician's pref- erence, clinical experience, safety profile, some degree of economics, insurance coverage, and judgment," he said. "The iStent has the most rigorous safety data. In most cases, the physician may describe the options to the patient, and that conversation will lead to a decision about which procedure will be per- formed." Dr. Sit said with all the options available on this front, selecting the right patient for the procedure, along with the surgeon considering his or her own comfort level, will be key. "For someone who is not used to working in the angle, it may be better to start with 1 of the proce- dures that is easier to adopt," he said. For example, "doing 360-de- gree trabeculotomies is a little bit more difficult than doing something like the Trabectome," Dr. Sit ex- plained. He also said if a surgeon is not comfortable with the data for a certain technique, he or she might consider holding off until more safe- ty and efficacy information becomes available. As for patient selection, Dr. Sit reiterated that MIGS are most effec- tive in patients with mild to moder- ate glaucoma. The type of glaucoma also factors into the equation, he said, noting that pseudoexfoliation glaucoma patients seem to do better with MIGS. While Dr. Sit uses Trabectome personally, he said he finds iTrack's microcatheter "very interesting" and thinks procedures that open the tra- becular meshwork more fully could have some advantages. A possible Addressing outflow Most MIGS procedures target the trabecular meshwork to facilitate outflow of aqueous humor, and there are several procedures designed to perform ab interno trabeculotomy that do not involve an implant. The Kahook Dual Blade is a single-use instrument that can excise a strip of the trabecular meshwork under gonioscopic visualization. Trab360 is a manual ab interno trabeculotome that can be used, as its name implies, to complete a 360-degree cut in the meshwork. Instead of a blade, Trab360 consists of an injected filament that once in Schlemm's canal is pulled to make the cut. The Visco360 device (Sight Sciences) achieves an ab interno viscocanalostomy by catheterizing the canal and by delivering visco- elastic as the filament is removed. The Trabectome is yet another device that targets the meshwork, ablating it, however, using irriga- tion, aspiration, and electrocautery instead of a blade. Taking a slightly different ap- proach, the illuminated iTrack 250A Microcatheter is designed to enlarge Schlemm's canal, but can be used for ab interno canaloplasty as well. The catheter enlarges the canal as it is fed around the angle and can then be removed by tearing open the tra- becular meshwork for 360 degrees. Stemming inflow Endoscopic cyclophotocoagulation, first developed in the early 1990s, reduces aqueous production from the get-go by using an 810-nm laser to ablate the ciliary body epitheli- um responsible for making aqueous humor. Many continued from page 44 These photos show a patient's trabecular meshwork before treatment (left) and after it was ablated with Trabectome (right), increasing aqueous outflow into Schlemm's canal. Source: Arthur Sit, MD " While we do have some published data, we don't have well-controlled, head-to-head trials, so it may come down to the physician's preference, clinical experience, safety profile, some degree of economics, insurance coverage, and judgment. " –Nathan Radcliffe, MD

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