Gonioscopy-Assisted Transluminal Trabeculotomy:

Blending Tradition With Innovation

The ab interno approach may prove to be the safest and most effective for glaucoma surgery.

By Aaron Barrett, MLS(ASCP), And Craig Chaya, MD

GATT in the Times

Gonioscopy-assisted transluminal trabeculotomy (GATT) is a minimally invasive, ab interno approach to a circumferential 360º trabeculotomy.1 This surgical technique lowers IOP by cleaving the trabecular meshwork, thereby improving aqueous outflow through the normal conventional pathway. Although often regarded as a pediatric glaucoma surgical technique,2,3 circumferential trabeculotomy has been shown to be effective in adults as well.4 GATT builds upon the success of traditional trabeculotomy by eliminating conjunctival and scleral dissection with an excellent safety profile.


The GATT procedure can be performed under either topical or intracameral anesthesia or retrobulbar block anesthesia from a temporal approach. Next, a paracentesis site is created either superiorly or inferiorly with its vector directed toward the nasal angle. Intracameral preservative-free lidocaine is injected into the anterior chamber, followed by a miotic agent and viscoelastic material. A temporal clear corneal wound of sufficient size is created, depending on whether or not GATT will be combined with cataract surgery. Next, the microscope and goniolens are oriented to maximize visualization of the nasal angle.

Then, a 1- to 2-clock hour goniotomy is created at the nasal angle via the temporal clear corneal incision (Figure 1). Additional viscoelastic can be used to gape the lips of the cut trabecular meshwork and to expose Schlemm canal.

Either a blunted suture or a microcatheter (iTrack microcatheter; Ellex) is introduced through the paracentesis and retrieved intracamerally with microsurgical forceps through the temporal corneal incision. The forceps are then used to guide the tip of the suture or microcatheter through the goniotomy cleft into Schlemm canal and to advance the tip around 360º (Figure 2).

When the iTrack microcatheter is used, the lighted tip can be visualized externally to confirm its correct position and progress. When a blunted suture is used, the position of the suture can be confirmed with a special goniolens that can visualize the entire angle intraoperatively, such as the Ocular Double Mirror Surgical Gonio Lens (Ocular Instruments).

After the suture or catheter has coursed through the entire canal, the tip appears on the opposite side of the goniotomy cleft. The leading tip is grasped with the microforceps and pulled to the center of the anterior chamber. Next, the external trailing end of the catheter is grasped near the paracentesis site. While the tip of the catheter is held securely with microsurgical forceps, gentle traction is applied to the externalized trailing end, creating a constricting loop that gradually cleaves the entire trabecular meshwork, completing the 360º ab interno trabeculotomy (Figure 3).

The catheter is then withdrawn through the paracentesis site, and the viscoelastic is aspirated from the anterior chamber. Postoperative drops include a steroid, an antibiotic, and pilocarpine.

Figure 1. A microvitreoretinal blade creates a goniotomy cleft
Figure 2. Microsurgical forceps guide the tip of the catheter into Schlemm canal.
Figure 3. Ab interno catheter loop is constricted to cleave the entire trabecular meshwork.



Grover and colleagues performed a retrospective chart review of 85 patients who underwent the GATT procedure.1 After 12 months, 57 patients with primary open-angle glaucoma experienced an 11.1 mm Hg (39.8%) decrease in IOP and needed 1.1 fewer glaucoma medications. In 28 patients with secondary glaucoma, IOP decreased by 19.9 mm Hg (56.8%) with an average of 1.9 fewer glaucoma medications needed at 12 months. The most common complication of the procedure was transient hyphema, seen in 30% of patients at the 1-week visit. Overall, GATT was safe and found to be effective in 68% to 90% of patients in this retrospective study.


A primary benefit of GATT is eliminating the need to incise the conjunctiva and sclera in order to navigate the trabecular meshwork. An ab interno approach also allows direct visualization of a so-called trabecular shelf that, when present, indicates an open, cleaved collector system commonly associated with a positive postoperative outcome.1 Other advantages include no conjunctival bleb formation, few postoperative complications, and successful outcomes in juvenile and adult glaucoma. As there is no violation of the conjunctiva, GATT employs a physiologic approach that leaves other options available for future filtration surgery.

On the downside, surgeons without experience performing gonioscopy-assisted procedures may initially struggle with GATT. GATT also requires a reasonably clear cornea to visualize the nasal angle, and therefore, a cloudy cornea would preclude this ab interno approach. Introducing instruments into the anterior chamber also poses an increased risk for damage to intraocular structures.


While long-term data are lacking and adoption of the technique has been limited, several important features of the GATT technique are worth noting. These include its ab interno approach, the maximal recruitment of all available collector channels, an excellent safety profile, and the avoidance of conjunctival dissection. As the field of glaucoma surgery evolves to include safer and more effective procedures, GATT may prove to be one such procedure for treating open-angle glaucoma patients.

Supported in part by an Unrestricted Grant from Research to Prevent Blindness, New York, New York, to the Department of Ophthalmology & Visual Sciences, University of Utah.

Section Editor Bala Ambati, MD, PhD, MBA, is a professor of ophthalmology and director of cornea research at the John A. Moran Eye Center of the University of Utah in Salt Lake City. Dr. Ambati may be reached at bala.ambati@utah.edu.

Aaron Barrett, MLS(ASCP), is a medical student at Creighton University School of Medicine in Omaha, Nebraska. He acknowledged no financial interest in the products or companies mentioned herein. Mr. Barrett may be reached at (801) 644-0083;aaronbarrett@creighton.edu.

Craig Chaya, MD, is an assistant clinical professor at the John A. Moran Eye Center of the University of Utah in Salt Lake City. He acknowledged no financial interest in the products or companies mentioned herein. Dr. Chaya may be reached at (801) 213-4044; craig.chaya@hsc.utah.edu.

  1. Grover DS, Godfrey DG, Smith O, et al. Gonioscopy-assisted transluminal trabeculotomy, ab interno trabeculotomy: technique report and preliminary results. Ophthalmology. 2014;121(4):855-861.
  2. Girkin CA, Marchase N, Cogen MS. Circumferential trabeculotomy with an illuminated microcatheter in congenital glaucomas. J Glaucoma. 2012;21(3):160-163.
  3. Dao JB, Sarkisian SR Jr, Freedman SF. Illuminated microcatheter-facilitated 360-degree trabeculotomy for refractory aphakic and juvenile open-angle glaucoma. J Glaucoma. 2014;23(7):449-454.
  4. Chin S, Nitta T, Shinmei Y, et al. Reduction of intraocular pressure using a modified 360-degree suture trabeculotomy technique in primary and secondary open-angle glaucoma: a pilot study. J Glaucoma. 2012;21(6):401-407.
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A Less Expensive Way to GATT, Marked suture aids GATT

A marked blunted suture can be visualized almost as well as a microcatheter and is more cost-effective.

Gonioscopy-assisted transluminal trabeculotomy performed with a thermally marked suture is a safe alternative to the same procedure with an illuminated microcatheter, according to a study.

The modified gonioscopy-assisted transluminal trabeculotomy (GATT) technique allows for visualization comparable to that of the original method.

GATT, a novel technique for performing an ab interno circumferential trabeculotomy, is safer and less invasive than traditional methods, according to corresponding author Davinder S. Grover, MD, MPH.

You really have a 70% to 80% chance of success of lowering the pressure to a very safe range without doing anything major to the eye, Grover told Ocular Surgery News. The advantage of GATT is that it can safely and effectively open up the patient’s own drainage system without making a major incision on the eye or doing any traditional glaucoma surgeries.”

In addition, GATT avoids many side effects associated with conventional glaucoma surgery, Grover said.

Basic technique

A 4-0 or 5-0 clear nylon suture is cut to a sufficient length to pass around Schlemms canal. An ophthalmic surgical marking pen is used to mark the tip of the suture, and then a heating source is used to blunt the tip. The ink is melted into the blunted tip of the catheter.

After standard sterilization measures, the eye is draped and an open wire nasal lid speculum is inserted to keep the eyelids open. A 23-gauge needle paracentesis track is placed in the superonasal or inferonasal quadrant.

Viscoelastic is injected into the anterior chamber, and a temporal paracentesis is created. A 4-0 or 5-0 nylon suture with a blunted tip is inserted into the anterior chamber through the entry site, with the tip resting in the nasal angle.

The patients head and the microscope are positioned to allow adequate visualization of the nasal angle with a goniolens.

A microsurgical blade is used to create a 1- to 2-mm goniotomy. Microsurgical forceps are inserted through the temporal site and used to grasp the marked suture within the anterior chamber.

The distal tip of the suture is inserted into canal at the goniotomy incision. Once inside the anterior chamber, the microsurgical forceps are used to insert the suture counterclockwise through the circumference of the canal.

A gonioprism can be used to visualize the progress of the suture.

A bimanual irrigation and aspiration system is used to remove the viscoelastic from the anterior chamber. The anterior chamber can be filled 25% with viscoelastic to help tamponade bleeding from the canal.

Postoperatively, subconjunctival or intracameral corticosteroid drops are given.

Suture vs. microcatheter

The microcatheter used in GATT can cost up to $800, Grover said. It is expensive, but the catheter is beneficial because it’s great for teaching and it’s great for learning because you can see the suture go around 360°. I think it really helps one learn the technique, and it helps people get a handle on how to do the surgery. I think it’s just an easier way to teach people, Grover said.

Experience with a catheter can prepare surgeons to use a suture, he said.

Once you get the hang of it and you know how to do the surgery and you feel comfortable with doing the surgery, then the exciting thing about it is that you can use the suture, which is a $4 technique, Grover said. Once people get comfortable with the catheter and get over some of the learning curve components of how you need to move things and how you have to manipulate the eye, the suture can be done just as easily and just as safely.

A marked suture can be visualized nearly as well as an illuminated microcatheter, Grover said.

When you mark the suture and then blunt it and then you look on gonioscopy, it’s easier to find than if you didn’t mark it he said. It still allows you to see where you are in the angle if you get held up or you need to find out where you are. The marked tip allows you to see that.

Additionally, GATT is significantly more cost-effective with a suture than with a microcatheter, Grover said.

It has tremendous implications in the United States for delivering cost-effective health care. But the exciting thing in my mind is that when you think about providing glaucoma surgical care in developing countries, this has a great potential to treat glaucoma safely and successfully without the long-term follow-up that traditional trabeculectomy or a tube would need, he said. “ by Matt Hasson

Disclosure: Grover reports no relevant financial disclosures.


Davinder S. Grover

The study was published in the Journal of Glaucoma.

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