GATT: Novel 360º ab interno glaucoma procedure

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Gonioscopy-assisted transluminal trabeculotomy is a circumferential trabeculotomy performed via a minimally invasive, ab interno approach. Results from follow-up of 6 to 12 months in a series of 85 adult eyes with uncontrolled glaucoma show high IOP lowering, along with a reduced need for medication.

Dr. Grover

By Cheryl Guttman Krader; Reviewed by Davinder S. Grover, MD, MPH 

Dallas-Gonioscopy-assisted transluminal trabeculotomy (GATT) is a novel, minimally invasive, ab interno glaucoma surgery that has demonstrated good safety and success in eyes representing a variety of types of open angle glaucoma, reported Davinder S. Grover, MD, MPH.

“Suture trabeculotomy has become the gold standard for glaucoma surgery in children, and there is good evidence supporting its effectiveness in adults with primary open angle and secondary glaucomas, said Dr. Grover, attending surgeon and clinician, Glaucoma Associates of Texas, Dallas. “However, ab externo trabeculotomy is a time-consuming, relatively invasive operation that requires numerous conjunctival and scleral sutures, and violates the conjunctiva so that it may preclude or diminish the success of subsequent trabeculectomy.

“GATT is a 360° ab interno procedure that is sutureless, spares the conjunctiva, and is relatively safe,” he continued. “Our preliminary experience demonstrates that it lowers intraocular pressure (IOP) and reduces medication burden equally to, if not better, than ab externo circumfererential trabeculotomy, and now we look forward to analyzing our results from longer follow-up.”

Dr. Grover credited Ronald Fellman, MD, Glaucoma Associates of Texas, with being the “mastermind” behind GATT, but also acknowledged the role his colleagues, Drs. David Godfrey and Tosin Smith, played in the development of this technique.

Understanding GATT

The procedure involves creating a goniotomy, cannulating Schlemm’s canal, and passing a suture or a micro-catheter 360°, circumnavigating the canal. The distal end of the suture/catheter is then retrieved and carefully externalized completing the trabeculotomy, without ever touching the conjunctiva.

“The procedure is easier to perform with the iTrack catheter (Ellex) because the illuminated tip allows the surgeon to know the exact location of the microcatheter at all times, unlike the suture tip,” noted Dr. Fellman.

Dr. Grover presented results of GATT from a retrospective analysis of data from 85 eyes with uncontrolled glaucoma. More details about the outcomes and the procedure can be found in an article published in Ophthalmology online ahead of print [Grover DS, et al. Ophthalmology. 2014 Jan 9 Epub ahead of print]. Follow-up was available to 6 months in 81 eyes and to 12 months in 36 eyes. The low follow-up rate at 12 months was explained by insufficient follow-up time and not loss due to failed outcome or other reasons.

The series included 57 eyes with primary open angle glaucoma (POAG) that were further divided for outcomes analyses into three subgroups based on whether they were pseudophakic or phakic and had GATT alone or combined with phacoemulsification. The other 28 eyes had various types of secondary glaucomas and either underwent GATT alone or with cataract extraction.

Mean preoperative IOP ranged from 23.8 to 25.6 mm Hg in the POAG subgroups and was higher (27.6 mm Hg and 31.8 mm Hg) in the two secondary glaucoma subgroups. Across all five subgroups, patients were using an average of 2.2 to 3.5 glaucoma medications.

Study results

After 6 months, patients with POAG had a mean 7.7 mm Hg decrease in IOP and were using 0.9 fewer glaucoma medications. Among the POAG eyes followed to 12 months, the mean IOP decrease was 11.1 mm Hg, and the medication burden was reduced by a mean of 1.1 agents.

The results were even better in the secondary glaucoma group, where at 6 months IOP had decreased by a mean of 17.2 mm Hg and medication use by a mean of 2.2. At 12 months, the mean decrease in IOP was 19.9 mm Hg and patients were using 1.9 fewer medications on average.

“The outcomes were better in eyes with secondary glaucomas where we know the pathology was in the trabecular meshwork,” Dr. Grover said. “Our data also showed results were similarly good regardless of lens status and that concurrent cataract surgery had no impact on outcomes.”

With failure defined as IOP >21 mm Hg after 6 or more months-or IOP not lowered at least 20% from baseline after 6 or more months, or need for another glaucoma surgery-Kaplan-Meier survival analysis showed the cumulative proportion of failure at 1 year ranged from 0.1 to 0.32 across the five subgroups. Eight eyes (9%) underwent further glaucoma surgery.

There was only one intraoperative complication-a case of capsular bag dehiscence and need for anterior vitrectomy in an eye with a secondary glaucoma undergoing a combined procedure. The most common postoperative complication was hyphema, which was mostly transient and seen at rates from 23% to 37% across the five subgroups at the 1-week follow-up. Five eyes experienced a steroid-induced IOP spike during the first month after surgery. The only other complication involved choroidal folds in one eye during the first postoperative week.

Davinder S. Grover, MD, MPH

E: dgrover@glaucomaassociates.com

Dr. Grover has no relevant financial interests to disclose.

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