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Nonpenetrating technique could be future of glaucoma surgery
Although still the gold standard, trabeculectomy can involve multiple complications. A transition away from filtering procedures is under way, doctor says.
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Transitioning from filter to nonpenetrating surgery could be the future of glaucoma, according to one physician.
Bradford J. Shingleton, MD, spoke at the OSN New York Symposium about techniques in glaucoma surgery. He said a dialogue should be started about making the transition from filters with penetrating, incisional surgery to bleb, or bleb-free, nonpenetrating surgery.
Trabeculectomy remains the gold standard of glaucoma surgery, he said, as it is one of the most effective ways of lowering IOP. It also reduces the number of medications and has a long track record. However, it potentially has multiple complications connected to the creation of the bleb, including hypotony, bleb leak, shallow anterior chamber, choroidal detachment and cataracts.
He said although newer technologies have not yet become standard practices, they could be the future of glaucoma surgery.
“We have modes of being able to make the transition for general ophthalmologists, but it takes some time,” Dr. Shingleton said. “Technology is certainly moving in that direction, and it’s not something that should be foreign to all of us. You can indeed make the transition with the conventional techniques that you’re using.”
Types of procedures
Ideally, nonpenetrating procedures do not create a bleb, Dr. Shingleton said. Ab externo approaches include viscocanalostomy, canaloplasty and EyePass from GMP. Ab interno approaches include excimer laser trabeculostomy, Trabectome from NeoMedix and the iStent from Glaukos.
Alternative procedures are also important, he said. Those procedures are mainly incisional and do not typically create blebs.
“In a sense, they are ‘nonpenetrating’ because they are not associated with trabeculectomy-type blebs,” Dr. Shingleton said. These procedures include tube shunts, goniotomy, trabeculectomy and goniosynechiolysis.
He said there are basically two types of nonpenetrating procedures. One group creates blebs, but is different from the traditional mitomycin-C trabeculectomy bleb, and one group uses implants. These procedures tend to have a more moderate, sustained lowering of IOP. They also reduce the number of medications, but there is a short track record, he said.
“The critical thing here is we don’t have all these hyperfiltering blebs,” Dr. Shingleton said. “As a result, the complications definitely are reduced in the early and the later postoperative period.”
Surgery technique
 Bradford J. Shingleton |
At the meeting in New York, Dr. Shingleton showed video of his nonpenetrating surgery and explained how he performs it. The surgical techniques are a filter procedure that is penetrating and creates a bleb, goes to a transition procedure and then a new nonpenetrating approach.
To transition to the nonpenetrating surgery, a fornix-based flap should first be created, he said. To achieve good exposure superiorly, he places a 6-0 silk suture at the inferior limbus and tucks it under the lid speculum.
After creating a “typical” triangular flap, Dr. Shingleton said he does something different to phase the penetration to nonpenetrating surgery. He creates a deeper flap and enters Schlemm’s canal. The deep flap must be created just above the suprachoroidal space with a thin “veneer” of sclera present over the choroid, he said. Schlemm’s canal will be unroofed as it is approached with this deep dissection. A clear Descemet’s window should be created with aqueous percolation present, he said.
“It’s incredible how often you can lift up juxtacanalicular tissue at the level of Schlemm’s canal and visualize it as a stiff, thick, rigid material. When you strip that off, it’s extraordinary how this tends to improve flow through that Descemet’s window,” Dr. Shingleton said.
Dr. Shingleton said he then does a dilation of Schlemm’s canal in viscocanalostomy. He said surgeons could stop there and not transition to a filter.
“If one wishes to transition to a filter, the deep scleral flap is closed and an incision is made into the anterior chamber underneath the superficial flap,” he said. A Descemet’s punch is used to create a posterior lip sclerectomy. A peripheral iridectomy is performed and the scleral/conjunctival flaps are closed as one would normally do for a filter, he said.
“Exposure of Schlemm’s canal is … the most technically challenging of the surgical techniques I’ve come to master. I feel comfortable with it now, but it takes time,” Dr. Shingleton said. New technology allows for a canaloplasty to be performed using the iScience technique, he said. It expands Schlemm’s canal for 360°.
Dr. Shingleton said he cannulates the fiber optic probe, placing the small beacon at the end of the probe into Schlemm’s canal and viscodilating the canal as it passed through Schlemm’s canal for 360°. It proceeds “remarkably smoothly,” he said. The microcannula exits out the other cut end of Schlemm’s canal.
“Tie one or two sutures to the tip of the microcannula, and pull it out. It will traverse in the reverse direction,” Dr. Shingleton said. “We will have successfully dilated first and cannulated Schlemm’s canal with a suture.”
He said evidence seems to suggest that tying the suture puts tension on Schlemm’s canal, which may facilitate the ultimate pressure control.
Finally, the flap is truncated and amputated. The superficial flap is tightly closed to create a space or “lake” underneath the flap, Dr. Shingleton said.
For more information:
- Bradford J. Shingleton, MD, can be reached at Ophthalmic Consultants of Boston, 50 Staniford St., Suite 600, Boston, MA 02114; 617-367-4800; fax: 617-589-0552; e-mail: bjshingleton@eyeboston.com. Dr. Shingleton is a consultant for or receives research grant support from Alcon, Allergan, Bausch & Lomb, iScience and Pfizer.
- Erin L. Boyle is an OSN Staff Writer who covers all aspects of ophthalmology.