spotlight on technology & technique
An Ab Interno Trabeculectomy for Open Angle Glaucoma
The Trabectome penetrates into Schlemm's canal to ablate trabecular meshwork and facilitate filtration.
By John Parkinson, Associate Editor

Glaucoma has garnered significant attention in recent years as new treatments have been created and new patient management options developed. One current effort to improve the surgical approach is the Trabectome system from NeoMedix.

This device enables the surgeon to perform an ab interno electrosurgical trabeculectomy. This new method ablates a segment of the trabecular meshwork and removes it as opposed to the traditional method of creating a filtering bleb.

The keystone feature of this system is a handpiece with a 19-gauge infusion sleeve, 25-gauge aspiration port, electrosurgical electrodes and an insulated footplate at its tip. The moderately sharp footplate can penetrate the trabecular meshwork, enter Schlemm's canal and feed the trabecular meshwork to the ablative electrodes with simultaneous infusion and aspiration controlled by a footswitch. A mobile console provides the infusion, aspiration, and electrosurgical energy.

George Baerveldt M.D., professor and chairman of the department of ophthalmology at the University of California, Irvine, and co-inventor of the Trabectome, began thinking about ways to remove a portion of the trabecular meshwork safely with a laser when he came upon the idea for this system. "I realized I needed a footplate to protect the collector channels in Schlemm's canal from the energy that was produced by the laser blasts. When I did that [conceived the footplate concept], I could use various other energies including electrocautery." Dr. Baerveldt found the idea of using electrosurgical elements appealing as this technology is well established in ophthalmic surgery.

The Trabectome system is equipped with an irrigation/aspiration console and high frequency generator, which are both mounted on the system's roller stand.

Screening and Prep

Donald Minckler M.D., professor and emeritus director of glaucoma services at the University of Southern California's Medical School, who participated in clinical studies of the Trabectome, suggests the procedure should be limited to patients who possess eyes with open angles and clear anatomy.

"The angle landmarks need to be clearly visualized; the ideal angle is grade 3 to 4 by the Schaefer scheme (Schaefer Advanced Glaucoma Evaluation System); and the trabecular meshwork needs to be easily identifiable," he explains. Open angles are important in order to navigate across the chamber, and easily identifiable meshwork pigment is important for recognizing the surgical target.

Dr. Baerveldt typically uses retrobulbar anesthesia for a Trabectome procedure. General anesthesia may be utilized in high myopes with very large globes, and in cases where retrobulbar cannot be delivered safely.

Surgical Technique

After the patient is prepped and draped, a 1.5-mm temporal clear corneal incision is made. The Trabectome is introduced and advanced across the anterior chamber with the infusion activated by the footswitch. The infusion deepens the anterior chamber and angle. A gonio lens is used to visualize the nasal angle. The footplate is advanced through the trabecular meshwork into Schlemm's canal.

The aspiration and cautery are activated while the surgeon advances the tip clockwise or counterclockwise, removing a 30š to50š strip of trabecular meshwork over Schlemm's canal, exposing the collector channels. The Trabectome is then removed from the eye.

A variable amount of reflux bleeding occurs as the intraocular pressure decreases. To control the blood reflux, irrigate with balanced salt solution, suture the corneal incision, and introduce an air bubble into the anterior chamber to increase the intraocular pressure.

Dr. Baerveldt surmises that the endothelial cells in the collector channels swell and create a valve mechanism to stop the blood reflux.

Post-Op

Dr. Baerveldt has been using prednisolone acetate (Pred Forte) 1% along with pilocarpine (Pilocar) 1.0% or 0.5% both q.i.d. for 2 weeks following surgery to maintain a constricted pupil and to help the meshwork cleft remain open.

The Trabectome has a specially designed bipolar surgical handpiece, which controls irrigation and aspiration. Operation is carried out with a footswitch.

Results

Thirty-seven adult open angle glaucoma patients were enrolled in a prospective clinical study of the Trabectome. One eye of each of the participants was studied. Only one patient's intraocular pressure (3%) failed to be controlled.

The mean preoperative pressure was 28.2 ± 4.4 mm Hg. The mean postoperative IOP at 1 day was 18.4 ± 10.9 mm Hg; 1 month 17.1 ± 5.4 mm Hg; 6 months 17.4 ± 3.5 mm Hg; and 13 months 15.5± 1.6 mm Hg. Intraoperative blood reflux occurred in all patients with clearing of the blood by 1 week.

As this type of surgery is not like a trabeculectomy with antimetabolites, the complications associated with bleb formation such as hypotony, bleb leaks, and bleb failure do not occur.

Physician Commentary

Anterior segment surgeons who are familiar with goniotomy in children will find this procedure easy to master according to Dr. Minckler. "It boils down to offering, potentially at least, a very simple way to accomplish an improvement in the outflow of aqueous that probably won't take a skilled operator more than 3 to 5 minutes," says Dr. Minckler.

Doctors have already achieved long-term results performing goniotomies or trabeculectomies on children due in large part to the makeup of children's meshwork. Dr. Minckler notes children's increased elastic tissue as opposed to adults' lack of elasticity in this area. Dr. Minckler is hopeful this new type of trabecular surgery can provide permanent filtration in adults.

"The theory we propose as to why this procedure works in adults," says Dr. Minckler, "is that because you are removing a strip of tissue, the gape you create persists. Whereas, if you just slice through this tissue, which is what's done with goniotomy, or rupture the meshwork inward as in trabeculectomy, you leave tissue behind. You don't actually remove a strip of tissue, you just disrupt it.

"The presumption is that in adults, because you don't remove the strip of tissue, there is a lot of debris and tissue fragments that can reconnect, seal, and scar so that the opening does not remain patent."

To solidify this theory, surgeons are continuing their studies of this potential breakthrough in surgical filtration.

Contact Information

The Trabectome system has been FDA approved, but is not yet available on the market. To find out more about the instrument and the procedure, call NeoMedix at (949) 248-7029 or visit the company Web site at www.neomedix.net.