Article

New insights into Trabectome

Analyses of our outcomes data with advanced statistical methods indicate an expanded use range.

Minimally invasive glaucoma surgery (MIGS) has changed the landscape of glaucoma treatment by offering a less-invasive option than filtering surgery or tube shunts. The main difference compared with traditional filtering surgeries is the reduced risk of complications,1 with reasonable effectiveness even after failed traditional surgeries.2,3

One of these minimally invasive modalities, the plasma-mediated ab interno trabeculectomy performed with the Trabectome (NeoMedix Corp), received FDA approval in 2004 for use in adult and pediatric glaucomas. It was more extensively described in 2006.4 The high-frequency bipolar electrodes generate a plasma cloud that is confined to the space in between the outer protective footplate and the two electrodes molecularizing tissue, similar to photodisruptive lasers (Figure 1). It is not a form of cautery and, unless excessive power levels are used, does not cause thermal coagulative damage due to a highly confined heat diffusion zone; this is commonly misunderstood when aspects of mechanical trabecular meshwork (TM) excision are discussed.5 This surgical procedure belongs to the family of ab interno trabeculectomy, which also includes erbium:YAG goniopuncture,6 excision with a goniotomy instrument,5 and peeling with subretinal forceps.7

Figure 1. Sketch of the tip of the Trabectome handpiece inserted into the trabecular meshwork. Plasma is generated between the active and return electrode that molecularizes the trabecular meshwork, similar to photodisruptive lasers. Thermal damage as seen in cautery does not occur. An active irrigation and aspiration system removes debris and maintains the chamber.

Trabeculectomy, long performed in pediatric glaucoma but historically with poorly sustained pressure reduction in adults with open-angle glaucoma (OAG),8 has experienced a rekindled interest in the form of ab interno-introduced Schlemm’s canal catheters9 and sutures.10 The key difference is that this type of trabeculectomy ablates the TM with a clean margin while trabeculotomy techniques leave irregularly torn TM edges. The outcomes of these different approaches have not been directly compared.

Although surgery with the Trabectome was previously felt to be relatively contraindicated for some types of glaucoma, clinical experience and recent literature have led to its expanded use. In this article, we review specifics of surgical technique, discuss expanded indications and examine the safety profile of Trabectome.

SURGICAL TECHNIQUE

Microincisional angle surgery presents unique challenges compared with traditional incisional glaucoma surgery. Here, we review the recommended surgical technique for trabeculectomy, although the general principles of working in the angle apply to other microincisional modalities.

Trabectome is often combined with phacoemulsification. In these cases, the angle procedure should be performed first to guarantee optimal visualization. If desired, Trypan blue can be injected to stain the trabecular meshwork.

A 1.8-mm keratome is used to create an iris-planar, clear corneal incision approximately 2 mm anterior to the temporal limbus. The surgeon should also make sure to flare the internal edges of the wound to accommodate the Trabectome (Figure 1).

If the larger keratome used in cataract surgery were employed, there would be too much fluid leak and surge. Unlike in other MIGS procedures, no viscoelastic is injected at this stage, as viscoelastic can carbonize Trabectome electrodes during ablation and create blurry density interfaces. Continuous irrigation and aspiration maintains the chamber well and allows the surgeon to perform goniosynechiolysis while debris is aspirated.

Next, the patient’s head is rotated away from the surgeon, and the microscope is tilted in the opposite direction. Slight pressure is placed on the posterior lip of the incision using the Trabectome handpiece; this induces hypotony and allows the surgeon to quickly identify Schlemm’s canal due to refluxing blood that highlights the target. The irrigation is turned on, and the Trabectome handpiece is inserted through the main incision. After a surgical goniolens is placed on the eye, the Trabectome tip can be visualized in the angle.

For right-handed surgeons, it is usually easiest to ablate in the counterclockwise direction first. The tip is engaged into the TM by pointing 45° upward just anterior to the scleral spur. The device is held strictly parallel to the TM with no outward pressure towards the canal wall while advancing. Then, the ablation continues for as far as visualization allows.

After completing the counterclockwise direction, the handpiece is flipped, and ablation is continued in the opposite direction. By tilting the goniolens towards the brow or the cheek, the superior and inferior angle is better visualized, and almost 180° of the trabecular meshwork can be treated.

After removing the Trabectome, the surgeon uses viscoelastic to tamponade the reflux of blood from the nasal angle. This reflux is desirable as it demonstrates successful ablation of the TM. If cataract surgery is planned, then the microscope and patient’s head are rotated back to primary position. To enlarge the incision for the phacoemulsification handpiece, the larger keratome is threaded through the previous incision with the heel of the keratome depressed. This creates a self-sealing, bi-planar wound suitable for phacoemulsification.11

We developed a pig eye training model for new surgeons that provides a safe training environment and allows the measurement of outflow change caused by this procedure.12,13 In our experience and in the operating room, trainees require on average 2.5 eyes to reach the half-maxima of their learning curve,14 indicating that five eyes are enough to become comfortable and safe with trabeculectomy in this species — trainees need nearly 30 eyes to excel and repeatedly produce reliable, high outflow improvement.

INDICATIONS AND USAGE

Combined with phacoemulsification

Trabeculectomy has been convincingly demonstrated to be a cost-effective option for the treatment of glaucoma.15 A range of OAGs can be treated that include pigmentary,16 steroid induced,17 pseudoexfoliation18 and uveitic glaucoma.19 As glaucoma and cataracts are often co-morbid conditions in our patients, combining these procedures is an excellent option for treating IOP and improving vision, while simultaneously limiting anesthesia and recovery times.

A patient undergoing phacoemulsification combined with Trabectome surgery can expect a roughly 18% decrease in IOP as patients with a mixed indication, often having a lower baseline IOP.20 In other words, contemplating the IOP reduction as a percentage of the preoperative IOP is misleading because Trabectome in phaco-Trabectome patients is not less effective than Trabectome surgery performed alone. In studies that use exact matching of phakic patients — who remain phakic — undergoing trabeculectomy, to phakic patients undergoing phaco-Trabectome, all patients have a similar pressure reduction, approximately 16 mm Hg postoperatively.21

This is a result of the Goldmann equation22 that predicts that, after TM removal, only the downstream elements (and the uveoscleral outflow) matter. Phacoemulsification also lacks a significant IOP reduction (only 0.7 mm Hg) when phaco-Trabectome is compared to Trabectome in patients who already had cataract surgery as shown in a separate study.23

Trabectome alone

Trabectome alone may also be a reasonable choice for patients who already underwent cataract surgery, as well as for patients who do not yet have visually significant cataracts. Reviews of patients undergoing trabeculectomy alone compared to phacotrabeculectomy demonstrate roughly equivalent postoperative IOPs in both groups (within about 1 mm Hg).23,24 In a recent review of phakic patients undergoing trabeculectomy alone as compared with phacotrabeculectomy, the phakic patients had a slightly larger decrease in IOP, suggesting that phacoemulsification is not a significant contributor to IOP-lowering in these patients.21

Figure 2. Steps of Trabectome surgery (from left to right): With the patient looking up into the microscope and the surgeon in temporal position, a clear corneal incision is fashioned that is parallel to the iris and relatively anterior (2 mm) to prevent iris prolapse. After the head is rotated away by 30° and the microscope is tilted towards the surgeon by the same amount, the incision is gaped to allow fluid egress and hypotony. This will cause reflux of venous blood into Schlemm’s canal and highlight the ablation target. The Trabectome is inserted and the TM is engaged towards the left, pointing up in a 45° angle. After entering Schlemm’s canal, the surgeon should keep the tip parallel to the TM and avoid outward pressure.

Narrow angles and angle closure glaucoma

Narrow angles were previously deemed a contraindication to trabeculectomy due to a perceived propensity towards synechiae and scarring. However, a recent review of patients undergoing trabeculectomy or phacotrabeculectomy did not find any difference in IOP lowering, number of medications or success rates in patients with narrow angles (Shaffer grade 2 or less) compared with open angles (Shaffer grade 3 or more).25

In the presence of anterior peripheral synechiae,25 the presence of an irrigation and aspiration system provides a view of the anterior chamber angle that is currently unrivaled by other instruments which rely on viscoelastics to maintain the space. This allows glaucoma surgeons to perform surgeries in secondary glaucoma or as a secondary procedure, as discussed below.

Failed trabeculectomy or tube shunt

Repeat procedures after failed incisional glaucoma surgery are often challenging due to conjunctival scarring and development of fibrosis. Trabectome does not violate the conjunctiva and therefore may be a viable alternative to repeat filtering or a shunting procedure.

Recent reviews have demonstrated success rates of 81% to 87% for patients undergoing Trabectome surgery after a failed trabeculectomy or tube shunt.2,3 This may result in up to a 36% reduction in IOP; about 25% of patients require further surgical intervention.26

Moderate to advanced glaucoma

We stratified 843 patients by a glaucoma severity index that combines IOP, number of medications and visual field damage to reflect the relative clinical resistance to treatment. A linear regression analysis showed that a higher IOP reduction was seen in more advanced stages of glaucoma after adjusting for age, gender, race, diagnosis, cup-to-disc ratio and angle-opening grade.24,27

The success rate at 12 months was 90% for mild glaucoma and 77% to 71% in moderate and severe glaucoma, respectively. This indicates that Trabectome has a role beyond mild glaucoma and ocular hypertension as the first line of treatment.

Alternative to tube shunting

Literature comparing Trabectome to tube shunts is more sparse. Recent research suggests that although Trabectome does not provide the same IOP-lowering effect that tube shunting does, it has significantly fewer complications and a lower reoperation rate.28,29 In our study that applied propensity score matching of Ahmed29 tube shunts to Trabectome patients and of Baerveldt28 tube shunts to Trabectome patients, glaucoma index results (combining IOP with the number of medications to achieve that IOP) are surprisingly very similar at one year and three years after surgery.

We suggest that patient selection will play a major role when determining the appropriate intervention; if a patient does not require ambitious lowering of IOP, then Trabectome may be an appropriate alternative to tube shunting.

Combined with tube shunting

While tube shunting has become a mainstay in glaucoma treatment, it has obvious drawbacks, including a relatively high complication rate as well as the well-documented hypertensive phase. Non-valved implants also involve an approximately six-week waiting period before the shunt opens.

Recent literature suggests that Trabectome combined with Baerveldt implantation may reduce patients’ IOP lowering medications postoperatively who have similar IOP and visual acuity outcomes; this may translate into an improved quality of life and reduced medication burden.30 Literature examining Trabectome combined with Ahmed implantation is also forthcoming; it is possible that the addition of Trabectome surgery may blunt the problematic hypertensive phase.

COMPLICATIONS

Compared with traditional glaucoma surgery, Trabectome has a highly favorable safety profile.1 A very common early postoperative observation is microhyphema and a layered hyphema that indicate a successful connection to a functioning outflow tract.

Side effects discerned in a meta-analysis that are not typically vision-threatening include peripheral anterior synechiae (14%), corneal injury (6%) and temporary IOP elevation (6%).1 Vision-threatening complications are rare and include prolonged but resolving hypotony (1.5%), iris injury (1%), cystoid macular edema (1.5% when combined with phacoemulsification), cataract progression (1.2%), a cyclodialysis cleft (two cases), aqueous misdirection (four cases), choroidal hemorrhage (one case), and endophthalmitis (one case).1 The rates of these events vary based on surgeon experience, and novice surgeons should expect a higher complication rate at the beginning of the learning curve.

CONCLUSION

Surgical options to treat glaucoma were previously very limited. Twelve years after its introduction, the Trabectome represents a conservative and safe surgical choice with a demonstrated track record. It makes for a compelling addition to the armamentarium of the comprehensive ophthalmologist and the glaucoma specialist. New surgeons can anticipate a learning curve of at least a handful of cases. Experienced surgeons can use the Trabectome even in complex cases, including angle closure, advanced glaucoma or following failed traditional glaucoma surgery. OM

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