Article

Matching glaucoma severity and surgical risk

Knowing when the patient’s situation calls for a Trabectome, tube or trabeculectomy.

With the MIGS revolution, glaucoma specialists have so many more options. The question is no longer a binary question of whether to trab or to tube. We now have the ability to exploit and enhance the conventional outflow system via Schlemm’s canal-based procedures as well as explore the suprachoroidal space. While we are still trying to better tailor the surgery to the patient, there are some guiding principles that we can depend on. Generally, patients with very mild disease have healthy collector channels and may not need a large portion of the canal opened. Patients with mild to moderate open angle glaucoma usually have an intact collector system; however, they typically benefit from having a larger section (or 360 degrees) of Schlemm’s canal opened. That said, it is generally agreed that patients with very advanced open angle glaucoma usually have a damaged and atropic collector system. These advanced open angle glaucoma patients almost always need a new outflow system (trab or tube). While we still do not have a method for evaluating outflow capacity in our patients, this categorization can be used as a proxy for outflow capacity until we have something better. – Davinder S. Grover, MD, MPH

There are now so many glaucoma surgery options it has become difficult to select the most appropriate one. Because glaucoma is a chronic, long-term disease, it follows that surgeons often make conservative, time-proven decisions and are skeptical of new devices and techniques. It is prudent to balance the reduced risks that new MIGS promise with knowledge about their long-term effectiveness of established procedures.

We feel there are three basic categories of glaucoma surgeries and recommend mastering one surgery in each.

  • The first type of surgery restores conventional outflow along its natural route.
  • The second bypasses a nonworking, conventional outflow tract by shunting aqueous into the subconjunctival or suprachoroidal space.
  • The third group achieves a very low intraocular pressure.

SPECIFICS

The most common procedures we perform in those categories in our practice are:

  1. Trabectome (NeoMedix) or Goniotome (NeoMedix) ab interno trabeculectomies
  2. Ahmed glaucoma drainage implants combined with Trabectome
  3. Trabeculectomies.

Because there are more surgical technique variations than there are glaucoma surgeons, we would like to explain our rationale and share our surgical pearls for these three procedures.

A PRISTINE VIEW

The Trabectome surgical system creates a high-frequency alternating current at the tip to molecularize and aspirate the trabecular meshwork.1,2 The energy is confined to the 50-micron space between the two electrodes and guarded towards the outer wall by a protective footplate. The mechanism is like ablative lasers that can create a highly confined plasma microbubble. Because it is surrounded by aqueous humor, it collapses immediately. In contrast to cautery, heat dissipation is negligible.

The most obvious difference between Trabectome surgery and MIGS procedures that have to be performed through a viscoelastic is the outstanding view of the anterior chamber angle and the trabecular meshwork. While viscoelastics are barely noticeable during cataract surgery, MIGS procedures require the surgeon to move and tilt the eye to view the nasal angle. This may cause viscoelastic to escape through the incision. The anterior chamber and angle may shallow progressively during the procedure.3 This causes depressurization and reflux of blood from Schlemm’s canal, which mixes with the remaining viscoelastic, further aggravating the view. However, the Trabectome and Goniotome3 each have an irrigation and aspiration port similar to cataract surgery. While the Trabectome comes with its own high-frequency generator and peristaltic pump, the Goniotome can be plugged into existing phacoemulsification or vitrectomy units.

NEW SKILLS

Over many years, we have developed several pearls to prepare beginning surgeons and allow them to excel at Trabectome and Goniotome surgery.1,2,4 Angle surgery is a new skill even for the most experienced cataract or cornea surgeon and requires patience and humility. The average beginner requires at least five eyes to become safe and comfortable with manipulation in the angle.4 However, it takes approximately 30 eyes to learn how to maximize outflow and achieve optimal results.4 Technique keys2 are: having an excellent microscope with sufficient tilt; creating a relatively anterior, iris planar, clear corneal incision that is slightly flared for a striae-free view through the cornea; avoidance of viscoelastic that can trap ablation bubbles; engagement of the TM slightly more towards the nondominant hand that holds the goniolens and with the tip pointing up at a 45-degree angle; hovering in Schlemm’s canal to avoid damage to the outer wall with its many collector channels; maximizing the ablation length in both directions; and combining pressurization with saline and viscoelastic at the surgery’s conclusion to avoid immediate post-procedural hypotony and blood reflux.

At the conclusion of surgery, we inject 100 microliters of undiluted moxifloxacin, using a cannula, under the iris that aims a gentle stream through the zonules. We also place 300 microliters of decanted triamcinolone under the upper conjunctiva with a 27-gauge needle. No postoperative drops are needed. We stopped postoperative pilocarpine years ago due to patient complaints of poor vision and we have not observed a difference in outcomes. All glaucoma drops are discontinued and can be added as deemed necessary. We instruct patients to not lift heavily and avoid pool and ocean water for one week. A clear shield is worn at night.

Figure 1. Goniotome and Trabectome. Left: The Goniotome has a serrated dual blade design with irrigation and aspiration ports for active chamber management. Right: The Trabectome with I&A and a high frequency generator for frictionless ablation.

LONG SAFETY RECORD

The Trabectome and Goniotome were conceived approximately 15 years ago.2 While the Trabectome allows for a completely drag-free ablation when used correctly, the Goniotome excises the TM with dual, serrated blades that ramp up and prestretch the TM before the strip is aspirated.3 The serrated blade design is unique to this device and produces a highly reliable, simultaneous dual cut.

In our opinion, the Goniotome represents a cost-conscious solution to TM ablation that is compatible with existing irrigation and aspiration systems. However, the experienced MIGS surgeon will prefer a full Trabectome unit to avoid any traction along the TM, and the iris and ciliary body processes that often insert into its distal portion. It has the longest track record of efficacy and safety of all MIGS, while the body of experience with the Goniotome or dual blade surgeries absent active chamber management is limited.3,5,6

In addition to primary open angle glaucoma, this procedure is effective in different types of glaucomas including pseudoexfoliation,7 inflammatory,8 pigmentary,9 steroid induced 10 and angle closure glaucoma.11 Active neovascularization is an absolute contraindication. Trabectome surgery is effective even in eyes that have failed trabeculectomies12 or tube shunts.13 Eyes with narrow angles can also be operated on, regardless of same session cataract surgery or not.11 Advanced glaucoma is not a contraindication to Trabectome or Goniotome surgery,1416 but the caveat is these eyes may be more likely to have an abnormal outflow resistance distal to the TM and may not be able to afford a nonresponse. However, for patients who are unafraid of potentially needing a second surgery with a tube shunt implantation or trabeculectomy, going through a primary Trabectome surgery that can be combined with cataract removal is a good choice that we perform often. That said, adding cataract surgery to Trabectome surgery does not result in improved outcomes.17,18

UNSTABLE ADVANCED GLAUCOMA

Since the Tube Versus Trabeculectomy study,19 more tube shunts are being implanted as primary surgeries,20 although the pendulum has started to swing again slightly toward trabeculectomies.21 Due to its relative ease in handling and favorable risk profile,22 we have adopted the Ahmed glaucoma valve (AGI, New World Medical) over the Baerveldt glaucoma implant (BGI, J&J Vision) as our primary procedure for advanced glaucoma. BGIs achieve a lower IOP than AGIs but have a 10 times higher risk of hypotony (4.5%) and a two-fold higher chance of severe vision loss (7%). Through the valve, AGIs provide predictable flow immediately after insertion. Both AGIs and BGIs often experience a hypertensive phase23 when a capsule forms around the implant. AGIs may be more affected than BGIs due to an earlier influx of aqueous humor and the associated cytokines and physical stretch of the forming capsule.

In our practice, we often combine AGIs with Trabectome surgery to reduce or eliminate the hypertensive phase. We find this minimizes aqueous humor flow toward the plate and reduces capsule formation as we have seen with BGIs.24 We recommend performing the Trabectome surgery first to see the angle clearly. This is followed by cataract surgery and the AGI implantation in the superotemporal quadrant.

We insert the primed device through a 5-mm perilimbal conjunctival incision that is 5 mm posterior to the limbus. It is secured with one single 8-0 nylon pass through one of the islets, about 10 mm posterior to the limbus. After trimming and inserting the tube, we use fibrin glue to place a scleral patch graft of 8x5 mm over the tube. The glue also closes the conjunctiva and can be aided by an additional stay stitch of vicryl on each side of the patch if there is conjunctival traction. We use the same postoperative regimen as above that requires no drops at all.

PRIMARY TRABECULECTOMIES

Despite its risks25 and high variability, trabeculectomy remains a powerful surgery that has potential to achieve low IOPs26 with few topical glaucoma medications.27

We used a small-incision trabeculectomy technique28 that does not require a traction suture or iridectomy (movie example29). The surgeon creates a small 3-mm limbal conjunctival incision at the 12-o’clock position. After opening the sub-Tenon’s space with a Blumenthal Conjunctiva Dissector (Katena Products), mitomycin C-soaked (0.4 mg/mL) sponges are applied for 3 minutes. A shallow, triangular scleral flap is fashioned, and the dissection is advanced with a bent crescent knife to reach into the peripheral cornea. The surgeon then sits temporally to perform any cataract surgery. After reseating to the superior position, the trabeculectomy continues.

Although repositioning adds to the case time, the flap creating can be best controlled in a fully pressurized eye. After fashioning a side port, the surgeon enters the anterior chamber underneath the scleral flap with a keratome and squares off the incision with the side port knife. Three punches are performed with a Kelly Punch (ASICO). The scleral flap is tied down with one to three 10-0 nylon sutures, the knots are buried, and the conjunctiva is closed with two 10-0 nylon wing sutures. The postoperative regimen is as described above, but the IOP can be managed by laser suture lysis, 5-fluorouracil injections and ocular massage. OM

REFERENCES

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