Trabeculotomy by Internal Approach: Trabectome

23 Trabeculectomy by Internal Approach: Trabectome

Kevin Kaplowitz, Igor I. Bussel, and Nils A. Loewen

Trabeculectomy performed ab interno with the Trabectome (NeoMedix, Tustin, CA) is an established minimally invasive glaucoma surgery (MIGS) with a decade’s worth of published results.1,2 The surgery is designed to increase conventional outflow via the physiological route. This chapter discusses the indications and technique for, and results and complications of, the using the Trabectome in primary and adjunctive surgery. The Trabectome can be expected to decrease the intraocular pressure (IOP) to an average of 15 mm Hg and the number of medications by one. IOP reduction depends on flow resistance downstream of the trabecular meshwork (TM) and is independent of preoperative IOP. The risk of vision-threatening complications is reported to be less than 1%. Thus, the Trabectome offers an effective and safe option for a wide range of glaucoma patients.

Case Presentation

An 81-year-old woman presents with worsening chronic angle-closure glaucoma having had a Descemet’s stripping automated endothelial keratoplasty with cataract surgery several years before. Her visual acuity has decreased to 20/150, with an IOP of 20 mm Hg despite maximal medical treatment including three topical medications and oral acetazolamide. The corneal specialist felt that the number of medications was contributing to anterior corneal edema. There was nearly 180 degrees of peripheral anterior synechiae with iridocorneal touch along the nasal circumference, and the patient was pseudophakic. The visual field showed a superior greater than inferior arcuate defect, and the vertical cup-to-disk ratio was 0.75 with inferior thinning. Surgery was performed with goniosynechialysis using the Trabectome tip to expose the nasal TM, followed by ablation of the TM (Fig. 23.1). After 1 year, the IOP had decreased to 12 mm Hg on only timolol drops, which helped allow the cornea to clear and improved the vision to 20/60.

The Procedure

Trabeculectomy was originally described as a mechanism of plasma surgery with a bipolar 550-kHz electrode that could ablate a nasal arc of TM through a gonioscopic view. It was designed to improve the aqueous outflow in cases of open-angle glaucomas while reducing the side-effect profile of external filtration procedures. The Trabectome system consists of four components: the disposable handpiece, the foot pedal, the cautery generator with a peristaltic irrigation-aspiration console, and the stand (Fig. 23.2).

Rationale Behind the Procedure

By removing the TM, the aqueous has direct access to Schlemm’s canal, which should significantly increase the rate of outflow by decreasing the amount of aqueous outflow resistance. Previous work over several decades has shown that the juxtacanalicular TM and endothelial cells in Schlemm’s canal offer the greatest source of aqueous outflow resistance.3 Because it is believed that only 35% of total resistance to aqueous outflow is found beyond the inner wall of Schlemm’s canal, techniques to allow the aqueous to bypass this region should greatly facilitate aqueous egress.4 There is a nonlinear relationship between the decrease in resistance and the increased area of trabeculotomy, at least partly because Schlemm’s canal is septated and is actually wider near the collector channel orifices,5 so a long ablation arc may expose more collector channel orifices directly to the anterior chamber.

Because the procedure does not rely on external filtering of the aqueous, only a single clear corneal incision is made. By leaving the conjunctiva untouched and without retaining any hardware in the eye, the side-effect profile of the procedure is much closer to that of phacoemulsification than that of traditional glaucoma filtration surgery.

Patient Selection

In the initial clinical report,1 the Trabectome was described for use in open-angle glaucomas (angles open to at least 20 degrees), because an adequate view of the meshwork is required to engage the instrument. It may be that with a smaller surface area, a narrow angle has a greater propensity for fibrosis or peripheral anterior synechiae (PASs) to close the surgical cleft made after removing the meshwork. This theory has been challenged with clinical data (see Safety, Efficacy, and Results, below). We now routinely operate on cases with a wide range of etiologies, including narrow angles, trauma, scleral buckles, and uveitis, as well as following failed trabeculectomy.6,7

To be positioned properly during the surgery, patients must be able to rotate either their neck or their entire axial core so that the surgeon is ensured a view of the angle through the goniolens. If the patient has a secondary glaucoma from increased episcleral pressure, then the IOP would not be expected to be lowered as significantly, because this procedure relies on the episcleral veins for aqueous drainage. Also, the increased episcleral pressure would increase the frequency of blood refluxing through Schlemm’s canal, potentially causing recurrent microhyphemas, which pose the risk of episodes of decreased vision and increased IOP.8 The only contraindication that has been widely reported in the literature is active neovascular glaucoma. This contraindication is not based on any published reports of complications following use of the Trabectome for neovascular glaucoma, but rather it is thought that attempting to ablate a vascularized angle will lead to excessive hyphema with a resultant higher risk of fibrosis closing the surgical cleft. Finally, because the TM is the target tissue, when there is heavier TM pigmentation, the surgical target site is highlighted. Patients with pigmentary glaucoma may have better IOP outcomes (see Safety, Efficacy, and Results, below).

Surgical Technique

This section describes the key steps to maximize the potential result of a lower postoperative IOP while minimizing potential complications. It is not absolutely necessary to stop systemic platelet inhibitors or anticoagulants, but this can be considered if it is safe to do so. Stopping blood thinners does not reduce the frequency of postoperative hyphemas because they are the result of flow reversal during early postoperative low pressure. However, if iris vessel bleeding results from traumatic injury with the tip, then the potential for bleeding is increased with these agents.

Stand-Alone Procedure

The tip of the 19.5-gauge handpiece is coated in a proprietary multilayered polymer with a pointed tip necessary to engage the TM while protecting the surrounding tissue from dissipated heat.9 The electrocautery unit operates at 550 kHz at 0.1 to 10 W.

The aspiration port is only 0.3 mm away from the electrode tip, so that ablated debris is quickly and effectively aspirated to keep the view clear, while the irrigation also helps keep the anterior chamber deep and improves the view.9 The irrigation and aspiration is controlled with the foot pedal. Position 1 activates continuous, nonlinear aspiration, and position 2 activates ablation. The aspiration has a maximum flow rate of 10 mL/minute.10 The foot pedal also has a black ball that activates continuous irrigation when it is tapped.

The preoperative preparation is identical to that for topical clear cornea phacoemulsification, with the addition of gonioscopy to confirm that the TM is visible. The surgeon sits temporally. As with phacoemulsification, a paracentesis should be created to inject 1% preservative-free lidocaine. The irrigation bottle should be raised as high as deemed safe for the optic nerve status, because this deepens the angle and improves the view. No viscoelastic is needed and actually could worsen the view by trapping gas bubbles from ablation.

The main incision should be 1.6 to 1.8 mm to enable a tight fit of the handpiece to keep the chamber maintained (Fig. 23.3). The incision should be uniplanar and parallel to the iris to improve the facile insertion of the handpiece. To reduce the risk of iris prolapse through the wound, the incision should be created 1 to 2 mm anterior to the limbus. If a beveled incision is made from the limbus, the entry into anterior chamber will also be 1 to 2 mm anterior to the limbus. To ablate more than 90 degrees in total, we recommend enlarging both internal sides of the wound. With a uniplanar wound and flaring the right and left internal corners, there is more room to sweep the handpiece to each side without causing significant corneal striae that will impair the view significantly.

Once the wound is created, a view of the TM must be established. The most commonly used goniolens is the direct modified Swan-Jacobs gonioscopy lens (Ocular Instruments, Bellingham, WA). No coupling gel is required but balanced salt solution should be applied to the cornea before placing the lens. For the clearest and deepest view, there should be almost 60 to 80 degrees between the chamber and the surgeon: 30 to 40 degrees from rotating the microscope downward, and 30 to 40 from rotating the patient’s head away from the surgeon. If the patient is unable to rotate the neck, then another option is rotating the entire axial core, although this may make it difficult to stabilize the surgeon’s hands. If the view is established but the TM cannot be found, a small amount of fluid egress out of the main wound will enable a temporary hypotony. Hypotony can allow blood to reflux into Schlemm’s canal, highlighting the target tissue (Fig. 23.4). Ablating the wrong structure likely accounts for many cases where excessive hyphemas are seen in the early postoperative period.

Once the gonioscopic view of the TM has been established, the handpiece is inserted and advanced across the anterior chamber while viewing through the goniolens (Fig. 23.5). The TM should be approached with the tip at an angle. The upward angle helps with the engagement of this thin tissue (Fig. 23.6). The other technique to improve engagement is to avoid approaching the TM from a perpendicular angle. The angle of approach should instead be greater than 90 degrees from the direction of ablation. Once the TM is engaged, the ablation arc should be swept in a smooth motion, because there is very little resistance once the correct space is entered (Fig. 23.7). While the ablation is performed, it is vital to exert a very slight inward force to counteract the natural outward pressure that accompanies the sweep, particularly as the tip nears the edge of the gonioscopic image at the superior and inferior poles, where the curvature is not reflected well in the image. The inward pull helps avoid direct damage from the tip to the small collector channels in the outer wall of Schlemm’s canal.

The ablation should be started at 0.8 mW, as was described in the original cases.1 The ideal power has not been investigated since then. If there is insufficient ablation, the power should not need to be increased by more than 1 to 3 mW. If the power is too high, blackened necrotic tissue will be seen at the ablation lip. The first 60 degrees of ablation can usually be accomplished without many adjustments, and we routinely approach 90 degrees of ablation in each direction. Rotating the goniolens in the direction of ablation can help widen the view at the superior and inferior poles. At the end of the arc, the tip is disengaged from the TM and rotated toward the iris by 180 degrees so that the ablation can be continued in the other direction. By ablating 180 degrees, the aqueous has direct access to at least 240 degrees of outflow because one opening through the TM can provide access to 60 degrees of Schlemm’s canal.11 After the second half of the arc is completed, injecting a viscoelastic crescent near the ablation zone minimizes postoperative hyphema from reflux through Schlemm’s canal. Our technique used in a consecutive series of 192 patients led to an IOP ≤ 18 mm Hg in 81%, IOP ≤ 15 in 52%, and an IOP ≤ 12 in 27% after 1 year.12

In narrow angles with peripheral anterior synechiae, the smooth tip of the Trabectome handpiece makes an excellent instrument for goniosynechialysis (Fig. 23.8). If the PAS is not densely adherent, simply sweeping them downward and posteriorly may remove them from the TM. Forceful movements should not be made, to avoid creating iridodialysis or a cyclodialysis cleft. If the synechiae are more adherent, they can be directly engaged with the tip and very gently peeled off of the TM.

Combined with Phacoemulsification

If the procedure is combined with phacoemulsification, the Trabectome surgery should be completed first. This enables a tighter incision and a watertight chamber during the Trabectome surgery. Following the ablation, the Trabectome is disengaged from the TM and removed from the incision, and viscoelastic can be injected near the ablation arc to minimize hyphema. The main wound can now be enlarged to the necessary size for phacoemulsification, and the wound should now be made triplanar. Capsulotomy and phacoemulsification can proceed as usual. If the angle is quite narrow and does not open with irrigation, the Trabectome surgery is sometimes performed after the removal of the cataract. Indeed, some surgeons prefer this technique to maximize the exposure of the TM. With this technique, the cataract incision should be closed with a suture, and the Trabectome tip can be inserted to one side of the suture. The placement of the suture effectively reduces the incision size to fit the Trabectome tip and helps maintain the anterior chamber. During irrigation and aspiration, some surgeons leave some viscoelastic near the nasal ablation site to minimize postoperative hyphema.

Complications Specific to the Procedure

Trabectome surgery has a safety profile that is similar to phacoemulsification especially when combined with phacoemulsification. An early postoperative hyphema that is the result of temporary flow reversal is common following a Trabectome surgery and should not be viewed as a significant complication. Hyphemas may occur far beyond the immediate postoperative period, but they are extremely rare. A series of 12 patients complained of transient blurring between 2 and 31 months after a Trabectome surgery and were found to have spontaneous reflux that was associated with an increase in IOP that averaged 12 mm Hg higher than the previous visit.8 In our experience of 800 cases, only one patient experienced recurrent hyphema. He had high myopia with an axial length of 27 mm and suffered associated IOP elevations. The hyphema stopped when anticoagulation with aspirin was discontinued and did not recur 6 months later when the aspirin was resumed.

Oct 29, 2018 | Posted by in OPHTHALMOLOGY | Comments Off on Trabeculotomy by Internal Approach: Trabectome
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