25 Gonioscopy-Assisted Transluminal Trabeculotomy A patient with mild to moderate glaucoma on maximal medical therapy presents with uncontrolled intraocular pressure (IOP) and an open angle with easy-to-define landmarks. The cornea is clear, the anterior chamber is deep, and the patient is not on chronic anticoagulant therapy. The surgeon and patient discuss using a microinvasive technique to improve the flow of aqueous into the patient’s natural clogged drainage system. The patient understands that if the flow cannot be improved into its own natural drain, the patient will need further, and more aggressive, surgery to create a new drainage system for the eye. It is explained that the gonioscopy-assisted transluminal trabeculotomy (GATT) procedure, which does not involve scleral or conjunctival incisions, does not negate the option of using more invasive and traditional glaucoma procedures, should they be required in the future. Depending on the patient’s lens status, this surgery can be safely performed as a stand-alone procedure or in combination with clear corneal cataract extraction. Trabeculotomy lowers the IOP by enhancing the aqueous flow through an incised trabecular meshwork (TM)–Schlemm’s canal complex consisting of the TM, the juxtacanalicular tissue (JCT), and the inner wall of Schlemm’s canal (IWSC); this complex is the area of greatest resistance to aqueous flow. This bleb-less procedure improves aqueous flow through the patient’s natural drainage system. Trabeculotomy has evolved from a loupe-assisted ab externo procedure into a modern-day gonioscopy-assisted ab interno circumferential minimally invasive glaucoma surgery (MIGS). Trabeculotomy was initially designed in 1962 for a young patient with glaucoma secondary to Marfan’s syndrome, with the hope that cleaving open a preexisting malformed angle would reduce the IOP.1 Others extended the surgical concept to adults when they learned of Grant’s2 work, which found that much of the resistance to outflow in adult eyes was in the TM–canal area. Grant believed trabeculotomy reduced outflow resistance by 75%, but subsequent investigations found, at lower perfusion pressures, that trabeculotomy realistically eliminated 40 to 50% of outflow resistance.3,4 Major advancements in trabeculotomy included the ability to navigate the canal, initially with a suture demonstrated by Redmond Smith,5 then identifying the canal under a scleral flap,6 circumnavigating the canal for 360 degrees,7 and later with a lighted microcatheter.8,9 Further advancements include the ability to open the canal for 360 degrees from an ab interno approach, without violating the conjunctiva or sclera, namely the GATT procedure.10 It is generally recognized that limited trabeculotomy with McPherson’s11 or Harms’s trabeculotomes yields suboptimal long-term results in adults. However, over the past decade, progress in technique and technology has improved outcomes in adult glaucomas, especially with circumferential trabeculotomy. For example, Chin et al12 found that 360-degree suture trabeculotomy ab externo was significantly more effective in lowering the IOP in adult primary and secondary glaucomas than was a limited metal trabeculotomy; the success rate was higher with the circumferential trabeculotomy, 84% versus 31%. Over the past decade, the indications for circumferential trabeculotomy have widened to encompass more adult glaucomas.13 This is due to the desire to reduce complications from filtration surgery, particularly bleb-related issues, and instead try to salvage the natural outflow channels of the eye. In addition, over the past decade, there has been a major surge in interest and innovation for angle-based procedures in the treatment of open-angle glaucoma, exemplified by the Trabectome (NeoMedix, Tustin, CA), canaloplasty, and trabecular microbypass with devices such as the iStent (Glaukos, Laguna Hills, CA) or the Hydrus (Ivantis, Irvine, CA). Canal-based MIGS includes either a trabecular bypass device (iStent) or opening the canal with a Trabectome, suture, or micro cather. All of these microinvasive techniques enable the surgeon to tailor the glaucoma procedure to the patient’s needs, lifestyle, degree of glaucoma damage, and inherent drainage system functionality. This is a major advancement in glaucoma care. The ability to enhance the circumferential flow of aqueous humor into the patient’s diseased natural drainage system is a major step forward in glaucoma surgery. Flow into the patient’s inherent collector system prevents all of the problems associated with trying to establish an artificial drain, through subconjunctival filtration. This minimally invasive approach avoids the problems related to blebs and tubes, and facilitates a rapid recovery. In addition, MIGS works well in conjunction with modern-day cataract surgery. One problem with MIGS is the inability to assess the condition of the collector channels before surgery. Understanding the status of the patient’s inherent drainage system is vital because there may be damage to the intrascleral portion of the collector channels in certain types of open-angle glaucomas. Even if the surgeon successfully implants a trabecular device, or cleaves the trabecular meshwork, the downstream collector channels may not be functional and thus the procedure may be doomed to fail (see Chapter 26). Patient selection is critical to the outcome of all ophthalmologic procedures, but especially to the outcome of glaucoma surgeries in which both the health of the collector channels and the unpredictability of wound healing may significantly alter success. Patient selection regarding canal-based surgery is difficult because the success of the canal procedure is tied to the health and integrity of the downstream collector channels, and as of yet, we do not have a reliable preoperative methodology to visualize and assess the collector channels. If the collector channels are badly damaged or occluded, then a canal procedure’s effect may be limited. Various studies have reported disparate MIGS outcomes, and we believe that the key factors that correlate with damaged collector channels are more severe disease, long duration of the disease, poorer condition of the ocular surface, and the presence of an intraoperative episcleral venous fluid wave (EVFW).14 Thus, younger patients are likely to be better candidates for canal-based procedures, as their collector channels have had less time to atrophy. This surgical approach is the opposite of filtration surgery, in which older patients who scar less tend to be better candidates. In addition, trabeculotomy is particularly well suited for patients with primary congenital glaucoma (PCG) and juvenile open-angle glaucomas (JOAG), because their drainage system was malformed and cleavage of the canal restores more normal flow. Careful preoperative gonioscopy is necessary for all GATT patient candidates, and if aberrant angle vessels or extensive peripheral anterior synechiae (PAS) are seen, we do not recommend the GATT procedure. Also, because one must perform several manipulations within the anterior chamber, a loose or unstable intraocular lens/bag complex is a contraindication to the GATT procedure. Patients with pigmentary and pseudoexfoliation glaucoma are good candidates, as excessive deposition of material typically causes increased resistance in the trabecular meshwork, and GATT is able to target the site of pathology. In addition, we have found the GATT procedure is often a reasonable option for patients with failed glaucoma drainage tubes or trabeculectomies as long as the angle is open. In patients with prior incisional glaucoma surgeries, one must evaluate the location of the tube or sclerostomy to ensure that Schlemm’s canal is not involved. We have also had relatively good experience with GATT in patients with steroid-induced glaucoma, glaucoma related to anti–vascular endothelial growth factor (VEGF) treatment, angle recession glaucoma, and certain types of uveitic glaucoma. Following a standard sterile preparation, the eye is draped and a nasal open wire lid speculum holds the eyelids open. A tangential (not radial), 23-gauge needle paracentesis track is placed through either the superonasal or inferonasal cornea. This first paracentesis track serves as the entry site for the microcatheter or thermally blunted suture. A viscoelastic (sodium hyaluronate) is injected into the anterior chamber through the initial tangential paracentesis site. A temporal paracentesis is created. When using a suture, the authors incorporate dye from the tip of the marking pen onto the thermally blunted tip of the 4-0 clear nylon suture (Fig. 25.1). This facilitates visualization of the suture tip as it circumnavigates the globe. This is not necessary with an Ellex lighted microcatheter (Ellex Medical Lasers, Adelaide, Australia), for it incorporates a blinking light at the tip of the catheter, facilitating visualization of the probe in the canal. We recommend mastering GATT with the microcatheter first, as we feel it is easier to learn the key portions of the technique before relying on the suture. Next, the suture or microcatheter is inserted into the anterior chamber through the entry site with the tip resting in the nasal angle. The microscope and the patient’s head are then oriented to allow proper visualization of the nasal angle with a Swan-Jacob goniolens. A 1- to 2-mm goniotomy in the anterior trabecular meshwork is created in the nasal angle with a microsurgical blade through the temporal site. The tip of the blade is used to slightly depress the posterior lip of the cleaved TM tissue to expose the canal. Typically, upon decompression of the eye, blood will reflux into the canal, facilitating identification of angle structures. Microsurgical forceps are then introduced through the temporal site and used to grasp the microcatheter or suture within the anterior chamber. The distal tip of the microcatheter is then inserted into Schlemm’s canal at the goniotomy incision. Within the anterior chamber, the microsurgical forceps are used to advance the catheter through the canal circumferentially for 360 degrees. When using a microcatheter, the surgeon can visco-dilate the canal as the catheter is being passed circumferentially, as this may improve the outcome (this has not been proven). If visco-dilation is performed, one must keep the catheter moving at all times, because if the catheter stops, a Descemet’s detachment can occur. The progress of the microcatheter is noted by observing the illuminated tip. When a suture is used, the progress of the suture can be appreciated through the use of a gonioprism or watching for the dye-stained tip externally through the limbus. After the catheter has passed 360 degrees around the canal, the distal catheter tip is grasped in the nasal angle and externalized through the temporal corneal incision, creating the first half of the 360-degree trabeculotomy. Traction is then placed on the proximal aspect of the catheter, thus completing the 360-degree ab interno trabeculotomy (Figs. 25.2 and 25.3). The viscoelastic is then removed from the anterior chamber by a two-handed irrigation aspiration system (through the previously created corneal paracenteses) to wash the anterior chamber of blood. Near the end of the procedure, a 25 to 50% anterior chamber filled with viscoelastic can be instilled to help tamponade bleeding from the canal. We vary the amount of viscoelastic fill depending on the degree of blood reflux and the extent and quality of an intraoperative EVFW. Leaving Healon in the anterior chamber protects against immediate postoperative hypotony and may decrease the chance of a significant postoperative hyphema. The wounds are hydrated and checked to ensure a watertight closure. Postoperative steroid (subconjunctival or intracameral) and antibiotic drops are given per the surgeon’s discretion. Figs. 25.2 and 25.3 summarize the key surgical steps with both the suture and catheter. In certain cases, the suture or microcatheter cannot be passed 360 degrees in one direction and stops at around 180 to 270 degrees. In these cases, the surgeon should create a new paracentesis site 180 degrees from where the catheter stopped, and use a gonioprism to perform an ab interno goniotomy directly over the site where the distal tip stopped. The distal end is retrieved from this new location, opening up part of the canal. A suture/microcatheter can then be passed in the opposite direction through an additional 23-gauge needle incision, thus completing a 360-degree trabeculotomy (Fig. 25.2). If initially the surgeon is unable to insert the microcatheter or suture into the canal, for example starting from an inferonasal approach, then the surgeon should withdraw and create a second superonasal paracentesis track, relocate the microcatheter or suture, and try again navigating the canal in the opposite direction.
Case Presentation
The Procedure
Rationale Behind the GATT Procedure
Patient Selection
Surgical Technique
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