Gonioscopy-Assisted Transluminal Trabeculotomy: A New Ray of Hope!

Glaucoma surgery has seen significant innovations over the past two decades in the form of modifications to penetrating, non-penetrating, and minimally invasive glaucoma surgery (MIGS). Trabeculectomy has stood the test of time, remaining the gold standard for over half a century. As a result of steep learning curves and high-costs, newer techniques are often not feasible in the developing world. Moreover, the long-term success of these procedures has not been fully demonstrated.

A recent innovation has changed the way that glaucoma surgery can be performed in a multitude of settings. The procedure is known as gonioscopy-assisted transluminal Trabeculotomy, or GATT. Developed at the Glaucoma Associates of Texas in Dallas, it is a minimally invasive surgical treatment for the management of open angle glaucoma. GATT is normally performed using an iTrack microcatheter, which has a lighted probe that allows for optimal visualization of the advancing catheter in the Schlemm’s canal. The alternative method, innovated for its low cost, is known as the suture GATT, which is done using a less expensive 5-0 Prolene suture. The pioneers of this procedure Dr. Grover and Dr. Fellman acknowledge the immense public health benefit that GATT can have, particularly in the developing world.

The instruments used in the GATT procedure are low temperature cautery, 5-0 prolene suture, 25 gauge MVR blade, healon-GV, MST forceps, Swan-Jacob gonioprism, and McPhersons forceps. The first step of this surgery is to carefully blunt the tip of the 5-0 prolene suture using low temperature cautery. After making a paracentesis, healon-GV is injected into the anterior chamber. The patient’s head is then tilted away from the surgeon, and the microscope is tilted towards the surgeon. This facilitates better visualization of angle structures when seen under the Swan-Jacob gonioprism. The Trabecular meshwork is identified, and using a 25 gauge MVR blade, an incision is made to open the Schlemm’s canal. The blunted tip of 5-0 prolene is introduced from the paracentesis inside the anterior chamber, and under gonioscopic visualization, it is threaded in the schlemm’s canal using MST forceps. With gentle strokes the prolene is pushed inside the Schlemm’s canal until the tip appears 270 to 360 degrees from the starting position. The tip of the prolene is again caught by the forceps, and the gonioprism is removed. From the paracentesis, the suture is pulled outside of the eye, tearing away the inner wall of Schlemm’s canal. Finally, viscoelastic is washed out of the eye using bimanual Irrigation-aspiration. The anterior chamber is formed with saline, and the blanching of limbal vessels is used to confirm the surgery’s success.

There are a number of advantages to the GATT procedure. First, it does not require incisions in the conjunctiva or the sclera, preserving these tissues if future surgery is needed. While other MIGS can be extremely expensive, suture GATT is done at a fraction of the cost. Additionally, GATT allows for reduced follow-up requirements, reduces the long-term risk of infection, and has a lower side effect profile than more invasive procedures. Although the GATT procedure is an advancement in the field of glaucoma surgery, it does not come without some limitations. Learning this technique requires the surgeon to have absolute mastery of intraoperative gonioscopy, ambidexterity, and understanding of angle structures.

To conclude, we feel that with practice and perseverance, GATT can emerge as a promising treatment option for primary open angle glaucoma in the developing world.

By,
Dr Swati U,
Glaucoma Consultant,
Aravind Eye Hospital,
Pondicerry

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