360-Degree Ab Interno Trabeculotomy

27 360-Degree Ab Interno Trabeculotomy

Steven R. Sarkisian, Jr. and Evan Allan

Case Presentation

An 80-year-old man presents to clinic with controlled intraocular pressure (IOP) in the mid-teens on two medications. He is phakic, and has mild-to-moderate open-angle glaucoma (OAG) by Humphrey visual field. Given his mild level of disease and relatively controlled IOP, treatment is cataract motivated. He likely does not need a filtration surgery and the associated risks. Surgery with the TRAB360™ surgical instrument (Sight Sciences, Menlo Park, CA) is a potential option that can be done in conjunction with phacoemulsification to minimize IOP spikes after cataract surgery and to decrease the medication burden.

The Procedure

The gold standard for the surgical treatment of glaucoma has historically been trabeculectomy with the use of antifibrotics. However, despite effectively lowering the IOP, the trabeculectomy procedure is not without the risk of postsurgical complications. Postsurgical hypotony and a lifetime risk of blebitis are two of the most serious postoperative complications after a trabeculectomy procedure.

More recently, increasing interest in rejuvenating the natural trabeculocanalicular outflow pathway has led to advancement in the surgical approach to treating OAG that avoids shunting aqueous humor to a nonphysiological drainage site and is less likely to result in postoperative hypotony.

Trabeculotomy lowers the IOP by improving the flow of aqueous through Schlemm’s canal and adjacent collector channels without bleb formation.15 Currently, the most common approach to trabeculotomy is ab externo, which requires an extensive conjunctival and scleral flap dissection that may diminish the success rate of a subsequent trabeculectomy. A few ab interno methods have been described, including using the Trabectome (NeoMedix, Tustin, CA) and gonioscopy-assisted transluminal trabeculotomy using either suture or novel dual-blade devices.6 A drawback to the Trabectome is its inability to perform 360-degree trabeculotomy.

A novel device that can perform 360-degree ab interno trabeculotomy is the TRAB360. This procedure is a minimally invasive way to surgically treat OAG. Further, this procedure results in lower the IOP without the formation of a conjunctival bleb.

The TRAB360 surgical Instrument is a “trabeculotome,” a nonpowered instrument intended for the manual cutting of the trabecular meshwork, or trabeculotomy (Fig. 27.1). It can be used to mechanically cut up to 360 degrees of trabecular meshwork.

Rationale Behind the Procedure

The TRAB360 offers several advantages over traditional, incisional glaucoma surgery and even other currently performed minimally invasive glaucoma surgery (MIGS).

First and foremost, traditional filtration or shunting surgery is fraught with both early and late complications, such as bleb leak, hypotony, suprachoroidal hemorrhage, blebitis, and endophthalmitis. The consequences can be severe. Patients with earlier disease burdens, may be amenable to more conservative surgery. Because the TRAB360 is bleb-less and conjunctiva-sparing, if the patient loses control of the IOP over time, further filtration or shunting options can still be used.

Research already has demonstrated the safety and efficacy of trabeculotomy in the adult population. Data for trabeculotomy in adults shows a sustained effect with good IOP lowering. This has been traditionally done externally and can be done either for 180 degrees or 360 degrees.711 The TRAB360 enables 360 degrees of trabecular meshwork unroofing.

Other MIGS procedures have downsides, which include difficult dissection or intraocular maneuvers, the high cost of equipment, and the need for a power source. Moreover, one does not need to worry about identifying Schlemm’s canal externally, which can be difficult in external trabeculotomy or canaloplasty. Lastly, there is no need for capital investment in equipment or a power source.

Patient Selection

During a surgeon’s learning curve with the device, suitable patients would include those with mild-to-moderate glaucoma that is generally controlled on medications. Once a surgeon is familiar with the use of the device, the procedure may be considered for more advanced OAG patients or those with higher IOP. Patients can be either phakic or pseudophakic, but they must have an open angle with a good view of the angle. The patient also should be able to tolerate some postoperative blurring secondary to transient hyphema. Other candidates for the procedure are patients for whom the surgeon does not want to subject to the risks of a filtration or shunting procedure, and patients with extremely poor conjunctiva (thin or scarred) or ocular surface disease.

Surgical Technique

The surgeon begins by using a keratome (1.5 to 2.8 mm) to make a temporal incision. Care must be taken to avoid any blood vessels at the limbus, as any bleeding can obscure the view by interfering with the interface. If the surgery is being performed topically, topical anesthetic will be instilled into the anterior chamber followed by a cohesive viscoelastic. It is important not to underinflate, as the view will be distorted more easily, but overinflation will collapse Schlemm’s canal, causing distortion of angle anatomy or difficulty entering the canal. Viscoelastic is then placed on the cornea.

The most important step surgically is obtaining a view of the angle anatomy and recognizing the structures. The patient’s head should be rotated away from the surgeon ~ 30 degrees and the microscope tilted toward the surgeon ~ 30 degrees. This is similar to other angle-based surgeries. A gonioprism or double mirror such as the Swann Jacobs, Hill, Vold, or Ritch lenses are used to assess the view of the angle. Often it is beneficial to increase magnification. It is essential to know the angle anatomy, because intraoperative gonioscopy with viscoelastic in the eye can be different from gonioscopy in the clinic as the viscoelastic may change the iris approach. It is not unheard of in patients with lightly pigmented trabecular meshwork and an overinflated anterior chamber for the surgeon to mistakenly identify the anterior ciliary body as the trabecular meshwork.

Next, the trabecular meshwork is incised with the tip of the device and the probe is advanced into Schlemm’s canal (Fig. 27.2). The device should be parallel to the iris, lest the surgeon distort the view by pushing on the posterior lip or the side of the incision. Sometimes the surgeon may have to back up the tip of the device from the insertion site and guide the probe into Schlemm’s canal. At this juncture, it is important not to guide the probe posterior to trabecular meshwork or to allow the probe to deflect off of the trabecular meshwork. If this should occur and not be recognized, the result can be trauma to the iris, iris root, or ciliary body. A cyclodialysis cleft can also occur.

Once the probe has been advanced 180 degrees, the surgeon uses a push-pull motion to unroof the trabecular meshwork to achieve 180 degrees of trabeculotomy (Fig. 27.3). Care must be taken not to allow the probe to back itself out during the trabeculotomy. Healon is placed to tamponade bleeding, and the device is reversed to perform the same procedure on the other 180 degrees of the angle.

Oct 29, 2018 | Posted by in OPHTHALMOLOGY | Comments Off on 360-Degree Ab Interno Trabeculotomy
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