Eyeworld

FALL 2024 | EYEWORLD | 81 G STRIKE! About the physicians Ying Han, MD, PhD Vice Chair for Clinical Services and Medical Director Department of Ophthalmology University of California, San Francisco San Francisco, California Jacob Kanter, MD Assistant Professor Johns Hopkins University Baltimore, Maryland Poonam Misra, MD Assistant Clinical Professor Department of Ophthalmology Glaucoma Center at Manhattan Eye, Ear & Throat Hospital, Northwell Zucker School of Medicine New York, New York by Liz Hillman Editorial Co-Director V arious patient scenarios, combined with surgeon preferences and com- fort with the procedures, dictates tube shunt placement for glaucoma patients. The different placement options allow the surgeons to knock down challenges in order to set the patient up for the greatest likelihood of tube shunt success. "I will do all three locations in different circumstances," said Jacob Kanter, MD. "Where you choose to place the tube is mul- tifactorial," said Poonam Misra, MD. Anterior chamber placement Dr. Misra said that anterior chamber is her pre- ferred location for tube shunts. "Normally we prefer to put them in the anterior chamber. It's a large enough space and the tube is visible when you examine the patient to confirm no obstruction of the lumen," Dr. Misra said. Dr. Kanter said that anterior chamber place- ment is the only choice for phakic patients and those who have not had retina surgery. "If they still have their lens, technically, it's possible to fit it in the sulcus, but it's very risky," Dr. Kanter said. "If you have someone who is a young patient, a steroid responder, or a young primary open angle glaucoma patient who has a clear lens and you decide to do a tube instead of a trabeculectomy, you have to put it in the anterior chamber." Dr. Kanter said procedurally anterior cham- ber placement is simpler because you can see the needle the whole time as you're making a track for the tube, and there is not a lot of risk for bleeding in this space. The biggest con for anterior chamber place- ment is the increased risk for corneal decom- pensation potentially leading to corneal failure. "Even in some cases, it might look perfect, but the cornea decompensates, and we have to remove the tube or keep it but move it to the sulcus more posterior," Dr. Kanter said. To avoid this, Dr. Misra said to make sure the tube is closer to the iris than the cornea (or at least midway between the two struc- tures). She said the bevel should be up, facing away from the iris. Dr. Misra said that with this placement, it's important to perform careful gonioscopy preop to make sure there is enough space in the area where you intend to place it and you are aware of any peripheral synechiae or scarring. It's also important to make sure your tube entry site is positioned posterior enough from the limbus to limit tube exposure risk in the future. Ying Han, MD, PhD, said anterior chamber placement is not her preferred location, but she will use this space if 1) the patient is phakic and young or 2) if the tube could get blocked by vitreous when placed at sulcus, such as with loose zonules. Sulcus placement Dr. Han said sulcus placement is her preferred location for tube shunts, primarily because of its protective effect on the corneal endothelium. She acknowledged that sulcus placement may be trickier, but the learning curve is not steep. All her fellows and residents are able to perform sulcus tube placement during training. Dr. Han said she enters 4 mm from the limbus using a 20-gauge MVR blade, which is bigger than the diameter of the tube, to make tube insertion easier. She finds there is almost no leakage because the tube is inserted through the ciliary body, and the ciliary body muscle constricts to prevent leaking. She doesn't find bleeding to be an issue due to the use of the sharp MVR blade to get through the ciliary body and use of viscoelastic to create space, smooth the path for the tube, and tamponade any bleeding. Dr. Han emphasized the importance of cre- ating a bevel-down configuration for the sulcus tube placement. This is to prevent the tube being plugged by the iris tissue, which occurs if a bevel-up tube is placed in the sulcus. She dilates the patient for sulcus tube placement to help with visualization. Dr. Kanter said sulcus placement is trickier from a visualization and space standpoint. For precise placement, he recommended using one of the guidewire techniques, which he and col- leagues published about earlier this year. 1 Tube placement: overcoming challenges with different options continued on page 82

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