Eyeworld

MARCH 2020 | EYEWORLD | 89 G Contact Harasymowycz: pavloh@igmtl.com Sheybani: sheybaniar@wustl.edu collector that might not have much pigmenta- tion, that collector may have been atrophic," Dr. Sheybani said. Verifying you hit a collector channel When stents are correctly placed, Dr. Harasy- mowycz said a blood reflux from the collector channel into Schlemm's canal through the orifice of the stents can be seen. "In addition, one can see the outflow during irrigation and aspiration of the viscoelas- tic, and a blanching of the vessels can be seen," Dr. Harasymowycz said. "Postoperatively at the slit lamp, our group correlated the amount of outflow seen through the collector channels and the amount of IOP lowering and number of medications used." 2 Overall, Dr. Harasymowycz said "we are looking forward to future tools that will help us measure outflow both pre- and postopera- tively, and help surgeons decide which specific collector channels to target, similar to coronary angiography when placing cardiac stents," Dr. Harasymowycz said. Microstent (Ivantis), he said it's more likely due to the size of the device to hit them. Dr. Harasymowycz also likes to identify the main collector channels with stents like Hydrus, but he sees it as less of a necessi- ty. Stents that bypass the trabecular mesh- work and dilate Schlemm's canal are less sensitive to exact placement and increase larger areas for outflow, he said. Finally, what about procedures, such as canaloplasty or goniotomy, that open up the angle all together, hitting many collector chan- nels along the way? Dr. Harasymowycz cited research that showed trabecular excision surger- ies expose a larger amount of collector channels and have greater areas of outflow as compared to trabecular stenting. 1 "One should remember, however, that tra- becular excision surgeries may induce postoper- ative inflammation with angle scarring that may raise IOP but can be reversed with YAG laser goniopuncture," he said. How to identify collector channels Dr. Harasymowycz said collector channels can be identified with gonioscopy in areas where there is increased trabecular meshwork pig- mentation or spontaneous blood reflux into the anterior chamber when the IOP is lowered below episcleral venous pressure. "When the angle has no pigmentation or a homogeneous distribution of pigment, or no blood reflux, it is very difficult to guess how close we are to the collector channels. In these cases, it is even more important to mark the cornea," he said. Dr. Harasymowycz explained that he marks the cornea at the limbus in order to see the dot during gonioscopy. Dr. Sheybani said he also looks for areas of hyperpigmentation. "I'm looking for a place that potentially might have had flow or still has flow because I'd rather get to a collector channel that's function- al. I worry a little bit when it's been awhile and a collector has not been functional. Say you have an area with a lot of pigmentation compared to one that doesn't. If there is an area behind a Targeting an area with increased pigmentation and blood reflux into Schlemm's canal (red line) adjacent to a blue mark on the cornea (black line) that identified a collector channel Source: Paul Harasymowycz, MD References 1. Fellman RL, Grover, DS. Episcleral venous fluid wave in the living human eye adjacent to microinvasive glaucoma surgery (MIGS) supports laboratory re- search: Outflow is limited circum- ferentially, conserved distally, and favored inferonasally. J Glaucoma. 2019;28:139–45. 2. Bostan C, Harasymowycz P. Episcleral venous outflow: A potential outcome marker for iStent surgery. J Glaucoma. 2017;26:1114–1119. Relevant disclosures Harasymowycz: Glaukos, Ivantis, New World Medical Sheybani: Allergan, Katena, Glaukos, Ivantis

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