Eyeworld

49 EW FEATURE May 2016 • Microinvasive glaucoma surgery (MIGS) doctor. The beauty of a goniolens is that nothing is reflected, Dr. Fellman said. He finds the Swan Jacob offers good magnification and beautiful clarity. Another common mistake that Dr. Fellman comes across with the lens is a failure to properly remove any debris when it comes out of the autoclave. It usually has a little bit of residue on it from calcium in the water that can sometimes coat the lens. "You have to take a wet Weck- Cel sponge and clean the bottom and top of it, and then your view is better," he said. Dr. Brown prefers the Transcend Vold goniolens (TVG) (Transcend Medical, Menlo Park, California), which he finds doesn't put as much pressure on the cornea. "It doesn't push fluid out of the eye quite so much," Dr. Brown said. The type of viscoelastic used here can also be important. For pres- surizing the eye, Dr. Brown prefers the cohesive Healon GV (Abbott Medical Optics, Abbott Park, Illinois) because it stays in the anterior chamber better. He then uses a sec- ond viscoelastic to keep the gonio- lens connected to the cornea so that air bubbles don't form in between. "The right viscoelastic maintains the connection between the lens and the cornea so the view is optimal," Dr. Brown said, adding that while he uses ProVisc (Alcon, Fort Worth, Texas) here, which works well, there is still room for improvement. Dr. Fellman also uses Healon GV for inside the eye. "It [depends on] the surgeon's preferences," he said, adding that he thinks some visco- elastics offer a better view than oth- ers, and if the surgeon is not happy, he or she may want to try a different viscoelastic on the next case. For keeping the goniolens connected to the cornea, he uses a viscoelastic as the coupling agent on some, while on others he simply uses balanced salt solution. Pearls for positioning To help determine how to position the microscope, Dr. Fellman recom- mended tilting it the same degree for all cases so that the surgeon memorizes the position. "Because the microscope has a tilt to it, I tilt it all the way until it stops," he said. "That's my endpoint on every case." Otherwise, the surgeon doesn't know where it stops every time. Also, when tilting the patient's head, it can be a bit of a guessing game. "I typically rotate the head about 35 degrees," he said, adding that the surgeon can't measure this and it is more of a feel; after the surgeon puts on the goniolens, he or she may need to move the head a bit more and adjust the oculars. This is something that those learning angle surgery can practice on routine cataract patients, Dr. Fellman suggested. "At the end of the case, in order to visualize the angle, you have to tilt the patient's head away from you and tilt the microscope toward you," he said. He suggested looking at the patient's angle on a normal case and seeing how it feels. Practitioners can then try balancing the goniolens in one hand and making a motion with the other as if they were performing the procedure to get a feel for it. It's also important to consider the microscope. While the quality of view for an average microscope is typically fine for external surgery or phacoemulsification, when it comes to angle surgery, this varies immensely, Dr. Fellman finds. "With the scopes that cost more, you get a better view," he said, adding that this is helpful for seeing fine angle structures such as Schlemm's canal, which is only 300 to 500 microns in size. To help determine if a patient is a good candidate for a MIGS proce- dure, surgeons have to examine the patient preoperatively with a gonio- prism to ensure that they can locate Schlemm's canal by first finding the scleral spur. The problem with looking directly for the canal is that while the trabecular meshwork is usually pigmented, other structures of the angle can be as well, which can lead to confusion, Dr. Fellman explained, adding that Schlemm's canal is just anterior to the scleral spur. "That's a steadfast landmark," he said. "If you're doing gonioscopy preoperatively and you can't find the scleral spur, the patient may not be a good candidate—you certain- ly don't want that to be your first case." Finding the angle To more easily find the angle in- traoperatively, Dr. Fellman recom- mended lowering the pressure in the eye so that surgeons can get a reflux of blood into the canal. "Now there is a red stripe that you can follow," he said. "When you lower the pressure in the eye, blood from the episcleral veins refluxes into the canal because you have reversed the pressure gradient." This normally is higher in the anterior chamber than in the episcleral veins, he explained. Once you have identified the canal, the infusion associated with some MIGS procedures washes the blood downstream, preventing excessive bleeding. Dr. Brown finds it preferable to stain the trabecular meshwork with trypan blue. "I put the trypan blue When the trabecular meshwork is stained with trypan blue, the canal lights up, making iStent placement easier. Source: Reay Brown, MD • Cross training by practicing both indirect (office) and direct (operating room) gonioscopic skills can help practitioners perfect the process. • To determine if a patient is a good anatomic candidate for a MIGS procedure, gonioscopically visualize several clock hours of the scleral spur preoperatively. • To identify Schlemm's canal intraoperatively, some physicians rely on a reflux of blood while others prefer trypan blue. AT A GLANCE continued on page 50

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