Article

Goniotome Trabecular Meshwork Excision

A cost-conscious solution to ab interno trabeculectomy with pristine angle view.

The demand for microincisional glaucoma surgeries (MIGS) has been steadily increasing as well informed patients demand safer alternatives to traditional filtering procedures.1 Almost all MIGS have an improved safety profile, a minimal recovery time, and a good long-term efficacy in several types of glaucoma2-6 and across a spectrum of disease severity that includes more advanced stages.7,8 Faster surgeries with fewer complications and that allow rapid recovery also help address the costs caused by an increasing glaucoma prevalence. In 2020, 80 million individuals will have this blinding disorder.9

MIGS may enhance the conventional outflow by bypassing or removing the trabecular meshwork (TM), facilitating uveoscleral outflow, increasing subconjunctival absorption, or reducing the aqueous humor production.10 Advances in the engineering of microsurgery devices have expanded MIGS instrumentation and enabled new strategies. Two of the most successful MIGS modalities in use for 15 years, Trabectome surgery (NeoMedix Corporation)11 and endocyclophotocoagulation (ECP; Endo Optiks),12 require a significant financial investment and are often adopted primarily by glaucoma specialists. The Trabectome is a device that molecularizes the TM in a microscopic, collapsible plasma cloud and provides an elegant, drag-free ablation but requires a high-frequency generator. Until recently, the pristine view and angle stability that an irrigation and aspiration system provides could only be obtained by making this commitment. The recent introduction of the Goniotome (NeoMedix) acknowledges this need and enables surgeons to provide a precise TM excision in a highly controlled and reliable fashion. The Goniotome was first described and patented by George Baerveldt and Roy Chuck in 2005. The Goniotome allows for the removal of the TM with a serrated, ramping, diverging two-blade device. It does not require a console, and can be used under viscoelastic, or with irrigation and aspiration from any device such as a phacoemulsification machine.

Enhancing Physiologic Outflow

Ab interno angle surgeries differ in how they remove or bypass the TM and how the anterior chamber is maintained. The Trabectome uses pico-lightning to generate plasma that disrupts the TM with minimal heat dissipation, the Kahook Dual Blade (KDB; New World Medical) excises the TM with dual blades, GATT (gonioscopy-assisted transluminal trabeculotomy) and Trab360 (Sight Sciences) tear through the TM using an illuminated catheter or curvilinear rod. The iStent (Glaukos Corporation) and the Hydrus (Ivantis Inc.) bypass the TM with a permanent implantable stent.

Many MIGS come with specific challenges, such as the need for additional viscoelastic device to form the anterior chamber, which may be associated with progressive angle narrowing during the procedure and trapping of regurgitating blood and bubbles.13 Placing stents near collector channels can be challenging. Mere visibility of a collector channel need not indicate a sufficient outflow capacity.14 Single entrance access to Schlemm canal typically achieves outflow limited to approximately 30 degrees of angle structures on each side.15 GATT and Trab360 can cause the leading end to deviate into the suprachoroidal space. GATT, Trab360, and ECP all require viscoelastic to maintain visibility. Progressive narrowing and indirect movements of the iris and lens occur when these devices are moved around in the anterior chamber. MIGS places an extreme demand on the surgeon’s motor control and equipment. Because it is so crucial to visualize the angle well in MIGS, any interference by viscoelastics, blood, or debris can be a serious obstacle. Until recently, the only system that actively maintained the anterior chamber with an irrigation-aspiration system was the Trabectome.16 The Goniotome was introduced to provide the same benefits without the need to invest in capital equipment.

Excising Trabecular Meshwork With Visual Clarity

In contrast to stents and scaffolds, a trabecular meshwork ablation creates a larger opening of Schlemm canal with direct access to the collector channels.17 Pediatric goniotomy creates a fine linear incision in the center of the TM creating lips that may approximate or adhere to collector channel orifices, the main reason that it has not been adopted more broadly in adult patients. GATT leaves similar TM lips that are ragged.

The Goniotome has a pointed tip that penetrates the TM with ease like that of the Trabectome (Figure 1) but instead of using 2 electrodes, it guides the TM onto a ramp, stretches it, and cuts it with serrated blades. These blades are “V” shaped from narrow to wide and make for easy entry without getting wedged into a tight Schlemm canal. The serrated edges of the blades ensure a reliable cut initiation that can perhaps best be compared to cutting bread with a serrated bread knife compared to with a smooth chef’s knife. Serrated edges more easily overcome the tissue breaking point and allow for immediate, repeat attempts if a cut is not initiated with the first tooth edge of the serrated blade. The TM is aspirated into the center of the Goniotome and held taut, simultaneously removing any debris, pigment, and blood.

Figure 1. Goniotome has 2 irrigation ports that maintain the chamber (blue arrows). The trabecular meshwork is put under stretch by the ramp of footplate and excised by a left and a right blade. The cut trabecular meshwork strip, blood and debris are aspirated into the tip (purple arrow). Note serrated blades that enhance TM excision. The third image shows the hand piece (A), the aspiration (B), and the Irrigation (C).

The active irrigation of the Goniotome not only ensures a deep angle throughout the procedure but also allows extending the length of the ablation. The tubing of the Goniotome can be connected to any ophthalmic surgical device with aspiration and irrigation. We prefer using phacoemulsification machines that have a well controlled inflow and outflow (Centurion; Alcon). The pressure is set to 80 cm H2O, the aspiration to 10 mL/min, with either fixed or linear control, and the vacuum is limited to 100 mmHg. It is also possible to simply use a pole stand for gravity-driven infusion while reducing the outflow with a clamp. This might be ideal in an environment where sutureless extracapsular cataract surgery is performed, for instance during mission trips.

Getting started with the Goniotome without prior angle surgery experience is surprisingly easy because the anterior chamber is well pressurized and without corneal striae. The surgical steps are similar to trabectome surgery:11,18 the surgeon is seated temporally as for phacoemulsification. First, a left-handed paracentesis is made, and lidocaine is injected and the eye pressurized with it without any viscoelastic. A temporal 1.6-mm to 1.8-mm incision is then made in the right-handed position just anteriorly to the limbus and parallel to the iris plane. If this is a standalone procedure, only the temporal incision is required. This incision is at the same clock hour the surgeon would otherwise use for phacoemulsification and would be the opposite for left-handed surgeons. The incision is slightly gaped to induce hypotony and allow blood to reflux into Schlemm canal. The patient’s head is rotated 30 degrees to 45 degrees away from the surgeon, and the microscope is tilted toward the surgeon by the same amount. Continuous irrigation is clicked on, and the Goniotome is inserted through the incision across the anterior chamber toward the nasal angle. Once in the eye, the active irrigation deepens the anterior chamber and provides a clear view of the angle. The surgical goniolens is placed on the cornea without pressure. This modified Swan-Jacob goniolens has a handle attached to the left of the lens for right-handed surgeons, but it requires a different model that has the handle attached to the right instead for left-handed surgeons. Other goniolenses that may have a half-Thornton ring attached to provide counter traction and facilitate implantation in the suprachoroidal space are not recommended, because they limit the free-floating lens rotation necessary to maximize the TM ablation length.

The tip of the Goniotome is inserted into Schlemm canal, aspiration is started, and excisional ablation continued counterclockwise for approximately 45 degrees to 90 degrees. The TM can be amputated by increasing the aspiration and slightly angling the instrument or by turning it around and engaging the strip from the other side. The instrument is turned around, inserted at the original starting point and the TM is removed into the opposite direction over a similar length. A maximal treatment of 180 degrees can provide an outflow of up to 270 degrees of outflow structures due to the additional 30 degrees of outflow beyond the ablation end points on each side. The active irrigation removes the TM, blood reflux, and debris to maintain clear media throughout the surgery (Figure 2). If phacoemulsification follows, the anterior chamber is filled with viscoelastic, and the same incision is enlarged with the cataract keratome in heel-down position to give the incision an inverted U-shape and make the incision self-sealing. The postoperative care is identical to Trabectome surgery and other angle surgeries. We flush 200 microliters of moxifloxacin through the zonules into the vitreous with an intracameral cannula and inject 200 microliters of decanted triamcinolone subconjunctivally. Pilocarpine is not required.19 No postoperative drops are needed. All glaucoma drops may be discontinued to avoid hypotony and reflux but can be restarted as needed.

Figure 2. A rounded footplate guides the tip along Schlemm canal and guards against outer wall damages. A footplate lifts the TM on the right and left onto serrated blades that cut the TM, allowing it to be aspirated into the aspiration port. Diverging, serrated blades (A), protective footplate (2), irrigation port (3), aspiration port (4), excised trabecular meshwork (5), intact trabecular meshwork (6a), unroofed Schlemm canal (6b).

Excellent View, Predictable Outcomes

The Goniotome shows negligible depth and angle fluctuation and excellent visibility during intrasurgical measurement with anterior segment optical coherence tomography (ASOCT; Visante by Zeiss Meditec) in an ex vivo model.13 The anterior chamber depth increased by 100% after insertion of the Goniotome and remained unchanged during the procedure. Immediate postoperative outflow enhancement was good. In another ex vivo pig eye study, 3 ab interno trabeculectomy instruments were compared: the Trabectome, the Goniotome, and the KDB.20 While all produced a significant IOP reduction, the Trabectome increased outflow slightly more than the Goniotome and the KDB.

Like the Trabectome, the Goniotome can be used in mild to severe glaucoma and in a variety of glaucoma types (narrow angles, pigmentary, steroid, and pseudoexfoliation glaucoma),3,5,6,21,22 including surgery after failed trabeculectomy7 or tube shunt implantation.23 It can be used in combination with cataract surgery or as a standalone procedure in phakic and pseudophakic glaucoma eyes.24,25 More recently, we reported Baerveldt glaucoma drainage implants with same-session Trabectome surgeries to lower IOP further and reduce medication dependence. This also allows to safely tie off the tube without the need for fenestrations.26 Similarly, when combined with Ahmed glaucoma drainage implants, the hypertensive phase can be avoided.27 Both the Trabectome and the Goniotome leave the conjunctiva intact for any future surgery.

GONIOTOME: A SURGEON’S PERSPECTIVE By Brian Francis, MD

Last year, just before its launch, I had the opportunity to use the Goniotome device in the first live surgeries (Figure 3). The instrument is produced as the Goniotome +I/A, which is attached to irrigation and aspiration and is performed under fluid, and the Goniotome, which has no tubing attached and is performed under viscoelastic. The following are my observations after using the device. The Goniotome IA device was attached to an Alcon Centurion phacoemulsification machine, but it can be paired with any irrigation and aspiration source.

Figure 3. Surgeon’s view of first surgery with Goniotome +I/A. The tip is hovering in Schlemm canal and the TM is stretched onto the dual serrated blades and aspirated. Compared to an anterior-chamber maintained by viscoelastic, the view is clear and free of blood and debris.

The tip is wider than the Trabectome (NeoMedix), due to the need to stretch out the trabecular meshwork (TM) to facilitate cutting the tissue. The Trabectome ablates the TM and does not require stretching it to remove it. The blades are “V” shaped and diverge at a small angle, making the heel of the device slightly wider than other devices. Due to the continuous irrigation and aspiration, the anterior chamber stability of Goniotome +I/A is very similar to Trabectome. The incision should be 1.7 mm to 1.8 mm to prevent fluid from escaping around the device. When combined with phacoemulsification, I prefer to perform the Trabectome and Goniotome +I/A surgery before the cataract removal for several reasons. The view is excellent as the cornea has no edema from the phaco instrument. The smaller incision performed first keeps the chamber more stable than a larger phacoemulsification incision. Due to the irrigation, the anterior chamber is quite deep even before removing the cataract. Since there is no ablation of tissue, the TM is cut in a long strip, which is aspirated into the port of the instrument. It can be severed by turning the tip around and cutting it in the opposite direction. The strip of tissue will then be removed via the aspiration port. Similar to the Trabectome, the continuous irrigation and aspiration wash out any reflux of blood from Schlemm canal, keeping the view clear.

The Goniotome without irrigation and aspiration and KDB procedures are very similar. They are both performed with viscoelastic in the anterior chamber. Both may require injection of more viscoelastic to expand the anterior chamber and push any blood reflux out of the TM view. When performed as a combined procedure with phacoemulsification, it is typically performed after the cataract is removed, due to an expanded anterior chamber. The strip of TM must be removed with Utrata or micro-grasper forceps. After the procedure, the anterior chamber must be flushed to remove viscoelastic and any remaining blood reflux.

Brian Francis, MD, is director of glaucoma services and the Rupert and Gertrude Steiger chair in Vision Research at the UCLA Doheny Eye Institute. Dr. Francis is a surgical trainer for NeoMedix. Reach him at bfrancis@doheny.org.

Conclusion

The Goniotome delivers the original idea of TM ablation as an effective, highly standardized, and easy-to-perform surgery. It can be readily connected to any ophthalmic device with irrigation and aspiration. GP

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