May 2015




Shedding light on GATT

by Maxine Lipner EyeWorld Senior Contributing Writer


This series of intraoperative photographs demonstrates the key portions of the gonioscopy-assisted transluminal trabeculotomy (GATT) surgery: A: Initially a goniotomy is created with a microvitreoretinal blade.

B: Schlemms canal is then cannulated with a microcatheter, using microsurgical forceps.

C: One can appreciate that the catheter has already been passed 23 clock hours around Schlemms canal.

D: Given the blinking red light on the distal end of the tip, one can follow the path of the catheter as it travels circumferentially around the canal. The catheter has passed 180 degrees around the canal.

E: The microcatheter has come full circle around the canal.

F: The distal tip of the catheter is retrieved within the anterior chamber using micro- surgical forceps. Blood reflux from Schlemms canal is normal and usually a prognostic indicator of a successful outcome as well as an intact distal collector system.

Source (all): Davinder Grover, MD

Revitalizing the natural drainage system

Helping to rejuvenate glaucoma patients own drainage system is the aim with the canal-based surgery known as GATT (gonioscopy-assisted transluminal trabeculotomy), according to Ronald L. Fellman, MD, Glaucoma Associates of Texas, Dallas. This conjunctival-sparing, low-complication procedure is a stark departure from trabeculectomy, which involves creation of an artificial drain. Now were trying to enhance the patients own natural drainage system instead of making an artificial one, Dr. Fellman said. Thats one thing were really excited about in canal-based surgery because if we could increase flow into the patients natural drainage system, thats much more physiologic than creating an artificial passageway. Performing GATT Davinder Grover, MD, Glaucoma Associates of Texas, who performed the first GATT procedure together with Dr. Fellman, elaborated on how it is done. First we make 2 small incisions in the cornea through which we do all of our manipulation, he said. Through 1 of the incisions the suture, or the catheter, goes in and through the other we use our microsurgical instrument to pass the suture or catheter around the drain. Once the suture is introduced into the eye, the strategy is to look at the nasal quadrant of the drainage system and cut down on the trabecular meshwork.

That gives us direct access to Schlemms canal, he said, adding that they then cannulate the canal with the suture or with the catheter, passing it around 360 degrees until the distal end can be retrieved. Traction is placed on the proximal and the distal end of the catheter, allowing for the creating of an ab interno 360-degree trab, he said.

Dr. Fellman said that this is different from the ab externo 360-degree trabeculotomy that was done in the past. When this was performed, the conjunctiva was opened and incisions were made in the sclera. That violated the territory for trabeculectomy, Dr. Fellman said. Thats why GATT is so specialits done ab interno, everything is done internally, and we never violate the conjunctiva or the sclera. The beauty of the procedure is it took an approach that used to be done externally and internalized it to make it a microinvasive technique, he said. At the same time it does not violate tissues that may need to be worked on later. In addition, the GATT procedure makes it possible to open all of the patients drains in one sitting.

Dr. Grover finds that those who tend to do best with GATT are those glaucoma patients for whom the trabecular meshwork is the primary pathology. Thats what were removing from the system, Dr. Grover said. He finds that patients with pseudoexfoliation glaucoma and those with juvenile open angle glaucoma or some type of developmental glaucoma, as well as traumatic and steroid- induced glaucoma, do well with GATT. In such cases, the success rate is about 7080%, he noted, adding that even for those in whom the procedure was not considered a home run, there is still a 60% to 70% chance of success.

In a retrospective study published in the February 2015 issue of the British Journal of Ophthalmology, a marked decrease in pressure was seen in cases involving primary congenital glaucoma and juvenile open angle patients. The mean decrease in IOP was from 27.3 to 14.8 mm Hg with the mean number of medications dropping from 2.6 to 0.86. Investigators found that 5 eyes of the 14 studied had a drop of greater than or equal to 15 mm Hg. Patients who tend to be best suited for GATT are those whose distal outflow system is still intact, Dr. Grover said. If you have glaucoma for 40 years and have been taking drops, your distal outflow system is likely to be atrophic, he said, adding that unfortunately this system cannot be imaged well. Dr. Grover said there are proxies for an intact drainage system, such as identifying mild to moderate glaucoma patients whose drainage system is likely to be healthier. He and Dr. Fellman have also described how intraoperatively, an episcleral venous wave could help to show patency of the patients collector system.1 After doing the GATT procedure, practitioners can irrigate balanced salt solution in the eye and then watch as the episcleral vessels blanch, he explained. You can see a wave of balanced salt solution going through the vessels and that, in our mind, is confirmation that a patient has a functioning inherent drainage system, Dr. Grover said.

First-line surgical approach

Dr. Grover views the procedure as another MIGS option. A lot of MIGS-based procedures are surgeries that try to enhance the patients own drainage system, he said, adding that several MIGS procedures are done in conjunction with cataract surgery, which is also an option for GATT. Dr. Fellman pointed out that the beauty of microinvasive surgery today is that it allows practitioners to tailor surgery to the patients stage of disease. Weve never had that before, he said. In the past we did the same operation in everyone regardless of the stage of disease because thats all we had. Dr. Grover views GATT as a first-line surgical approach for glaucoma. I tell my patients that this is one of the safest, easiest, and least invasive things we can do in terms of glaucoma surgery, he said. The beauty of the surgery is it doesnt violate the conjunctiva, so its an easy go-to as an initial surgical approach. He explains to patients that if they succeed with GATT, they can potentially avoid a lifelong risk of infection and avoid putting a piece of hardware in the eye that involves concerns about double vision or erosion. He considers the procedure for mild to moderate glaucoma patients who do not need particularly low pressure. They are patients who function well with a pressure in the mid-teens, he said. Also for patients who need cataract surgery who are on several medications, its a great way to treat them.

Patients who are not candidates

GATT is not for everyone, however. If a patient has very advanced glaucoma and I know they need a pressure of 10, they need a trab without question, Dr. Grover said. In addition, because there is some bleeding, although transient, if a patient has a predisposition to bleeding or cannot be taken off blood thinners, Dr. Grover avoids the procedure. Also, theres a lot of manipulation in the anterior chamber, so if the patient has an unstable IOL we dont want to do that because youre going to disrupt the IOL, he said. Likewise, he finds that patients who have undergone penetrating keratoplasty will most likely end up needing a tube, so his bias is to avoid GATT in these cases. Because patients need to lie on their back with their head slightly elevated for about 1 or 2 weeks postop to avoid hyphema, that is a consideration as well, Dr. Grover said.

Take-home message

As Dr. Fellman explained, GATT allows surgeons to tailor the procedure to the patients stage of disease and lifestyle. It fits the lifestyle of a younger, more active patient without, Dr. Fellman said. Dr. Grover said that with trabeculectomy or a tube shunt there is a relatively high rate of hypotony, choroidal detachment, and choroidal effusions; practitioners do not have that fear of hypotony or any hypotony-related complications with a GATT procedure.

When first trying GATT, there can be a bit of a learning process, Dr. Fellman said. It takes a certain skill set to do a scleral flap, for example, when youre doing a trabeculectomy, he said, adding that it is different when you are working in the angle where other techniques are used. Dr. Grover concurred. He advised that those who are interested in learning GATT become comfortable working in the angle. You need to know angle anatomy and be comfortable doing angle-based surgery, holding a gonioprism onto the eye with one hand and manipulating things with the other hand, Dr. Grover said. While GATT is certainly not something anyone can learn in a day, he has found that those who are already well versed at angle surgery will become comfortable much more rapidly. Weve seen skilled surgeons who are comfortable in the angle, and they can pick it up in a short period of time, he said. For those practitioners who have not done angle surgery, the learning curve might ultimately be a little steeper.


1. Fellman RL, Grover DS. Episcleral venous fluid wave: Intraoperative evidence for patency of the conventional collector system. J Glaucoma. 2014 Aug;23(6):34750.

2. Grover DS, Smith O, Fellman RL et al. Gonioscopy assisted transluminal trabeculotomy: an ab interno circumferential trabeculotomy for the treatment of primary congenital glaucoma and juvenile open angle glaucoma. Br J Ophthalmol. 2015 Feb 12. (Epub ahead of print) 3. Grover DS, Godfrey DG, Smith, et al. Gonioscopy-assisted transluminal trabeculectomy, ab interno trabeculectomy: technique report and preliminary results. Ophthalmology. 2014 Apr;121(4):85561.

Editors note: Drs. Grover and Fellman have no financial interests related to their comments.

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