Ab Interno Trabeculotomy
Felipe A. Medeiros, MD; Sameh Mosaed, MD; Andreas Boehm, MD; and Robert N. Weinreb, MD
A 79-year-old white male was first examined in January 2001 and diagnosed with advanced primary open-angle glaucoma. His medical history included anticoagulation for chronic atrial fibrillation. The patient began topical ocular hypotensive treatment followed by argon laser trabeculoplasty, but his IOP remained high. In October 2002, he underwent uncomplicated phacoemulsification with a lens implant combined with trabeculectomy. His IOP was well controlled for 2 years but then increased. The patient underwent another trabeculectomy in November 2004. One year later, his IOP increased again. In July 2006, the patient developed progressive changes to his optic disc and visual field despite maximum tolerated medical therapy.
Comments on the Treatment Options
SM: This patient is on maximum tolerated medical therapy, and he presents with an IOP above the target as well as progressive optic nerve and visual field changes. My surgical options for this patient include another trabeculectomy, the implantation of a glaucoma drainage device, or an ab interno trabeculotomy. Given that the patient is anticoagulated, drainage device surgery would pose a significant risk of hemorrhage. Also, the chances of success with a trabeculectomy are lower, due to his history of two previous failures. Therefore, an ab interno trabeculotomy using the Trabectome (NeoMedix Corporation, Tustin, CA) is my preference.1,2
FAM: In this patient, a substantial decrease in the IOP is necessary to avoid further disease progression. How would this influence your choice of the surgical procedure?
RNW: Trabeculectomy often results in a significant reduction of the IOP. In a patient who has a history of two failed trabeculectomies, however, the chances of the procedure’s success are small. A drainage device may have a better chance of success. In a patient with a bleeding tendency, however, as pointed out by Dr. Mosaed, the risks of hemorrhage and failure are increased. With ab interno trabeculotomy, an IOP in the single digits is rarely achieved, because it cannot decrease below the episcleral venous pressure. Nevertheless, the procedure has the advantages of no conjunctival manipulation and only a small chance of hemorrhage. If additional lowering of the IOP is required after ab interno trabeculotomy, one could add topical medication.
Dr. Mosaed, would you describe the ab interno trabeculotomy procedure using the Trabectome?
SM: The device cauterizes and removes a portion of the trabecular meshwork and the inner wall of the Schlemm’s canal (Figures 1 to 3). The procedure is performed under direct gonioscopic view, and the surgeon usually ablates from 60º to 180º of the trabecular meshwork. Ab interno trabeculotomy essentially re-establishes aqueous drainage in eyes that have a diminished outflow facility. It should reduce some of the risks associated with trabeculectomy or aqueous drainage devices such as hypotony, a flat anterior chamber, or bleb-related infections.
Figure 1. Key features of the Trabectome’s handpiece include I/A ports, the electrocautery element, and an insulating shoe.
Figure 2. In this schematic representation, the trabecular meshwork and inner wall of Schlemm’s canal are ablated to allow the direct flow of aqueous through the aqueous collector channels (arrows).
Figure 3. In this intraoperative view, the Trabectome’s handpiece is engaged in the trabecular meshwork. A small cleft of ablation forms behind the trailing end of the handpiece.
RNW: Is there a difference from conventional goniotomy?
SM: One of the reasons why conventional goniotomy does not work well in adults is that the surgeon simply makes a cut on the trabecular meshwork without excising or cauterizing the tissues. The cut ends of the trabecular meshwork tend to fold back into their original position and scar together. With the Trabectome, the surgeon ablates (excises) the tissue, thus cauterizing the cut ends so they are less likely to reapproximate and close.
RNW: What are your current indications for using the Trabectome?
SM: Only approximately 150 patients have undergone the procedure in the US at the time of this writing. The indications and contraindications for ab interno trabeculotomy with the device have therefore been changing as surgeons acquire more experience. My current indications include patients with IOPs above their target on maximum tolerated medical therapy, those with progressive optic nerve and/or visual field loss despite maximum tolerated medical therapy, or those in whom conventional surgery to reduce their IOP has been unsuccessful.
The relative contraindications for the procedure include opaque corneas or extensive peripheral anterior synechiae, which impair the surgeon’s access to or visualization of the angle structures. I also usually do not recommend this procedure for patients whose IOPs are in the low teens but require further reduction. My colleagues and I have found that the procedure is more effective for patients who start off with higher levels of IOP.
RNW: Have you performed this procedure as an alternative to medical therapy?
SM: Yes, the procedure should be considered in patients who cannot tolerate topical medication or who are poorly compliant.
RNW: Can the procedure be performed in phakic patients?
SM: The Trabectome may be used in phakic patients and also as part of a combined procedure with phacoemulsification and IOL implantation.
FAM: Is there any correlation between the degree of ablation and the reduction of IOP?
SM: We have not yet evaluated this correlation, but we hope to in the future.
RNW: What are the potential complications of this procedure?
SM: A small hyphema, perhaps from a reflux of blood from Schlemm’s canal, occurs in the majority of cases. It usually resolves spontaneously in a few days. There is also a potential risk of infection (because a clear corneal incision is needed for access to the angle structures) and of corneal abrasion from the goniolens.
AB: Is there a risk of an IOP spike in the postoperative period? If so, is it correlated to the amount of ablation?
SM: I have seen IOP spikes in only a few cases. One of the patients had to undergo conventional trabeculectomy to lower his IOP.
FAM: What is the success rate of the procedure in terms of lowering IOP?
SM: My colleagues and I have an 80% early success rate, defined as an IOP of less than 21 mm Hg or a 30% reduction from the preoperative IOP, with or without the simultaneous use of IOP-lowering medications. Fifty percent of our patients required no concomitant treatment after the procedure.
As noted by Dr. Mosaed, ab interno trabeculotomy with the Trabectome is generally safe and can effectively reduce IOP in many, but not all, patients. Additional evaluation is needed to better delineate the appropriate indications for the procedure, specific surgical technique, and postoperative management.
Section editors Felipe A. Medeiros, MD, and Robert N. Weinreb, MD, are glaucoma specialists at the Hamilton Glaucoma Center, University of California, San Diego. Dr. Medeiros is Assistant Professor, and Dr. Weinreb is Distinguished Professor of Ophthalmology and Director. They acknowledged no financial interest in the products or companies mentioned herein. Dr. Medeiros may be reached at (858) 822-4592; email@example.com. Dr. Weinreb may be reached at firstname.lastname@example.org.
Andreas Boehm, MD, is Vice Chair for the Department of Ophthalmology, University of Dresden, Germany. He acknowledged no financial interest in the products or companies mentioned herein.
Sameh Mosaed, MD, is Assistant Professor for the Department of Ophthalmology at the University of California, Irvine. She acknowledged no financial interest in the products or companies mentioned herein.
1. Francis BA, See RF, Rao NA, et al. Ab interno trabeculectomy: development of a novel device (Trabectome) and surgery for open-angle glaucoma. J Glaucoma. 2006;15:68-73.
2. Minckler DS, Baerveldt G, Alfaro MR, Francis BA. Clinical results with the Trabectome for treatment of open-angle glaucoma. Ophthalmology. 2005;112:962-967.
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