TRABECULECTOMY
Technical Progress
In his keynote address,1 Robert Weinreb, MD, of the Hamilton Glaucoma Center in San Diego shared the Association of International Glaucoma Societies' recently published “consensus guidelines.”2 They address issues in glaucoma surgery for open-angle glaucoma (OAG), including the indications for as well as pros and cons of various surgical procedures. For most patients, medical treatment is still primary. “For most, but not all patients, trabeculectomy is considered the procedure of choice in previously unoperated eyes,” said Dr. Weinreb.1,2
Peng Khaw, PhD, FRCS, of Moorfields Eye Hospital in London elegantly demonstrated several practical modifications to trabeculectomy techniques to enhance the procedure's success rates and reduce potential complications3 (Figure 1). Among his suggestions was to avoid discomfort for the patient by positioning the bleb entirely beneath the upper lid. He said a fornix-based approach, with a diffusely applied antifibrotic covering a larger surface area of the conjunctiva, may help to reduce the occurrence of cystic, focal blebs (Figure 2). To maintain posterior flow, he suggested a flap of adequate size with its sides intact 1 mm posterior to the limbus. Dr. Khaw also remarked that the intraoperative use of continuous infusion may permit a better assessment of flow and avoid sudden intraoperative decreases in IOP. He further noted that adjustable sutures allow a controlled, gradual reduction in IOP, and he uses transconjunctival forceps to adjust the sutures' tension. Finally, Dr. Khaw also commented that meticulous attention to corneal/conjunctival closure can avoid leaking blebs.
Figure 1. Dr. Khaw illustrated surgical techniques to enhance the success of trabeculectomy, including the application of an antimetabolite to a large treatment area.
Figure 2. The incorporation of the trabeculectomy techniques described in Figure 1 promotes diffuse, low, filtering blebs (right eye) and reduces the risk of focally elevated blebs (left eye).
Reduced IOP Fluctuation
Swiss researchers prospectively compared IOP fluctuations in patients with well-controlled IOP who had undergone trabeculectomy (n = 20), deep sclerectomy with a collagen implant (n = 20), or therapy with latanoprost 0.005% once daily (n = 20).4 They evaluated diurnal IOP measurements taken between 8:00 am and 9:00 pm at 3-hour intervals.
At baseline, the IOPs were significantly lower in the trabeculectomy group (10.0 ± 4.4 mm Hg) compared with the deep sclerectomy (13.9 ± 2.8 mm Hg) and latanoprost (15.5 ± 2.0 mm Hg) groups. At all time points, the fluctuations in diurnal IOP were significantly lower in the trabeculectomy group than in the latanoprost or deep sclerectomy group.
Efficacy in Asian American and White Patients
Researchers at the Jules Stein Eye Institute in Los Angeles compared the efficacy and survival of trabeculectomy with intraoperative mitomycin C between Asian American (n = 29) and white patients (n = 29).5 Patients were matched case to case for age, type of glaucoma, preoperative IOP, medication history, and surgeon. The mean follow-up durations were 40.11 ± 22.5 months and 38.8 ± 17.7 months for Asian Americans and whites, respectively. Success was defined as an IOP of less than 22 mm Hg or a greater than 20% reduction in IOP. Trabeculectomy survival at 1 and 4 years for Asian Americans was 76% and 57%, respectively, versus 83% and 67%, respectively, in whites. There were no significant differences for the rates of surgical success, failure, or complications such as decreased vision, hypotony, and cataract development between Asian American and white patients undergoing trabeculectomy.
NONPENETRATING GLAUCOMA SURGERY
Overview
An innovator in glaucoma surgical techniques, Dr. Mermoud discussed the experience with and results of nonpenetrating glaucoma surgery.6 The primary goal of nonpenetrating techniques is to direct aqueous humor from the anterior chamber to Schlemm's canal by removing the main site of resistance at the level of the trabeculum and inner wall of Schlemm's canal.
Although nonpenetrating glaucoma surgery is generally considered to have a low rate of short-term postoperative complications, reports indicate that it is technically more difficult to perform than trabeculectomy and requires more time. Evidence in the literature to support nonpenetrating glaucoma surgery's efficacy is somewhat conflicting. Research shows a similar or reduced effect compared with trabeculectomy in the short and medium terms. Nonpenetrating surgical approaches may result in higher postoperative IOP levels compared with trabeculectomy, and many patients will require late goniopuncture.7
Deep Sclerectomy With Microshunt
Dr. Mermoud suggested that posterior deep sclerectomy in combination with a microshunt between the anterior chamber and intrascleral space may obviate the need for goniopuncture. He described a pilot study in which nine patients with primary open-angle glaucoma underwent deep sclerectomy and the insertion of the Optonol DS version microtube (Optonol Ltd., Zug, Switzerland) into the anterior chamber. At the 5-month follow-up, preliminary data indicated that the procedure was well tolerated, the implant was correctly placed, and the IOP had decreased.8 Studies are ongoing, and medium-term results are expected soon.
Viscocanalostomy Versus Phacoviscocanalostomy
In a prospective, consecutive study of 135 surgical procedures in Buenos Aires, Argentina, surgeons performed viscocanalostomy (n = 83) and phacoviscocanalostomy (n = 54) in white patients (mean age, 64 years) mainly suffering from OAG.9 Success was defined as an IOP lower than 20 mm Hg; the need for medication was considered a partial success. At 5 years, total and partial successes were 59% and 26%, respectively, for viscocanalostomy versus 77% and 21.6%, respectively, for phacoviscocanalostomy. Goniopuncture was needed in 26% of viscocanalostomy and 17% of phacoviscocanalostomy cases.
GLAUCOMA DRAINAGE DEVICES
Investigators presented the prospective Tube Versus Trabeculectomy Study, in which enrolled patients (N = 212) underwent either standard trabeculectomy or tube shunt surgery with a 350-mm2 Baerveldt implant (Advanced Medical Optics, Inc., Santa Ana, CA).10 The IOP results were reportedly similar, although slightly lower in the trabeculectomy group. The intraoperative complications appeared to be comparable between the two groups as did the need to return to the OR. The detailed, 1-year results of this study should be published soon.
Researchers from Toronto reviewed the records of 83 eyes of 77 patients undergoing either the superior or inferior placement of an Ahmed Glaucoma Valve (New World Medical, Inc., Rancho Cucamonga, CA).11 There were no differences in the age, gender, number of prior glaucoma surgeries, preoperative IOP, or number of preoperative medications between these two groups. Success was defined as a postoperative IOP of between 5 and 21 mm Hg and at least a 20% IOP reduction. Success rates between the superiorly and inferiorly placed valves did not differ significantly and, at 30 months, were 66.7% and 70.9%, respectively. The investigators reported higher complication rates (eg, hyphema, uveitis, diplopia, and the need for reoperation) in subjects receiving an inferiorly placed implant.
NEW SURGICAL METHODS
Trabectome in Adult OAG
Investigators from Irvine, California, and Geneva presented their surgical outcomes with the Trabectome (Neomedix Inc., San Juan Capistrano, CA), a device that ablates the trabecular meshwork.12 The removal of a strip of trabecular meshwork overlying Schlemm's canal was expected to provide access to the collector channels.
A prospective, nonrandomized study assessed the surgical outcomes of the Trabectome in one eye of each of 49 patients with OAG (mean age, 63 ± 11 years; follow-up, 3 to 24 months).12 Investigators removed 60º of trabecular meshwork by clear corneal incision. The mean preoperative IOPs decreased from 28.4 ± 4.2 mm Hg to 17.9 ± 3.5, 17.0 ± 2.2, and 15.7 ± 2.2 mm Hg at 6, 12, and 18 months, respectively. Complications included localized peripheral anterior synechiae and blood reflux in the first postoperative week (n = 14) and transient Descemet's changes (n = 6).
360º Canaloplasty With Microcatheter and Suture
In an attempt to enhance circumferential outflow by microsurgery within Schlemm's canal, investigators developed the technique of introducing a flexible microcatheter into Schlemm's canal from a scleral cut-down.13 After injecting viscoelastic to dilate the canal and performing 360º of catheterization of the canal, the surgeon pulled a Prolene suture (Ethicon Inc., Somerville, NJ) into the canal and tied the ends in an effort to provide tension to the trabecular meshwork. The scleral flap was sutured tightly to avoid bleb formation. High-definition ultrasound imaging identified the canal pre-and postoperatively, with follow-up to 12 months.
A prospective, surgical study involving US, European, and South African sites is evaluating this technique in a multicenter trial of patients with primary OAG and an IOP higher than 21 mm Hg with or without medication. Among the 66 patients enrolled, the safety profile appears to be acceptable, and, at 6 months, a reduction in IOP is evident. Additional data are forthcoming from this ongoing study.
ANTERIOR SEGMENT OCULAR COHERENCE TOMOGRAPHY
Using anterior segment ocular coherence tomography, Charles Pavlin, MD—a pioneer in ultrasound imaging—and co-investigators Richard Lee, BSc, and Dr. Ahmed examined the effect of slit-lamp illumination on angle assessment with gonioscopy.14 They evaluated 20 eyes to assess the changes in angle anatomy under different lighting conditions with Shaffer angle grades of less than 2. A light calibrated to the brightness of a slit lamp was used to simulate gonioscopic illumination, and scans were performed in the dark with light on the iris and within the pupil. Ten eyes demonstrated a change of one equivalent Shaffer angle grade. The investigators concluded that light artifact from slit-lamp gonioscopy may contribute to highly variable examination results. Anterior segment ocular coherence tomography may be helpful in the objective evaluation of the angle under consistently dark conditions.
Neeru Gupta, MD, PhD, FRCSC, DABO, is Associate Professor of Ophthalmology & Vision Sciences and Laboratory Medicine & Pathobiology. Dr. Gupta is Director, Glaucoma and Nerve Protection Unit, St. Michael's Hospital, University of Toronto. She acknowledged no financial interest in the products or companies mentioned herein. Dr. Gupta may be reached at (416) 864-5444; guptan@smh.toronto.on.ca.
1. Weinreb RN. Glaucoma misconceptions and realities. Keynote lecture presented at: The 3rd International Congress on Glaucoma Surgery; May 27, 2006; Toronto, Canada.
2. Weinreb RN, Crowston JG, eds. Glaucoma Surgery: Open Angle Glaucoma, Consensus Series-2. Association of International Glaucoma Societies. The Hague, The Netherlands: Kugler Publications; 2005.
3. Khaw P. Trabeculectomy: state of play. Keynote lecture presented at: The 3rd International Congress on Glaucoma Surgery; May 26, 2006; Toronto, Canada.
4. Mansouri K, Mermoud A, Haefliger I, et al. Fluctuations of IOP in medically controlled versus surgically controlled glaucomatous patients: a prospective trial. Paper presented at: The 3rd International Congress on Glaucoma Surgery; May 27, 2006; Toronto, Canada.
5. Law S, Modjtahedi S, Mansury A, Caprioli J. Intermediate-term comparison of trabeculectomy with intraoperative mitomycin-c between Asian American and Caucasian glaucoma patients: a case-controlled comparison. Paper presented at: The 3rd International Congress on Glaucoma Surgery; May 26, 2006; Toronto, Canada.
6. Mermoud A. Non-penetrating glaucoma surgery: state of play. Paper presented at: The 3rd International Congress on Glaucoma Surgery; May 26, 2006; Toronto, Canada.
7. Anand N. Nd:YAG laser goniopuncture to lower intraocular pressure following deep sclerectomy. Poster presented at: The 3rd International Congress on Glaucoma Surgery; May 26, 2006; Toronto, Canada.
8. Pournaras J-A C, Mermoud A. Safety and efficacy of the Optonol DS version microtube implanted under deep sclerectomy in POAG patients: preliminary results. Poster presented at: The 3rd International Congress on Glaucoma Surgery; May 26, 2006; Toronto, Canada.
9. Zanutigh V, Perrone D, Logioco C, da Silva M. Long term results (5 years) of viscocanalostomy and phacoviscocanalostomy. Paper presented at: The 3rd International Congress on Glaucoma Surgery; May 26, 2006; Toronto, Canada.
10. Reynolds AC. Tube Versus Trabeculectomy Study (TVT): one year results. Paper presented at: The 3rd International Congress on Glaucoma Surgery; May 26, 2006; Toronto, Canada.
11. Rachmiel R, Flanagan J, Buys Y, et al. Intermediate outcome of superior versus inferior Ahmed Glaucoma Valve implantation: surgical success and complications. Paper presented at: The 3rd International Congress on Glaucoma Surgery; May 26, 2006; Toronto, Canada.
12. Baerveldt G, Minckler D, Ramirez M, et al. Surgical outcomes of Trabectome in adult open angle glaucoma. Paper presented at: The 3rd International Congress on Glaucoma Surgery; May 26, 2006; Toronto, Canada.
13. Crandall AS, Lewis RA, Fellman R, et al. 360 degree canaloplasty with novel microcatheter and suture. Paper presented at: The 3rd International Congress on Glaucoma Surgery; May 26, 2006; Toronto, Canada.
14. Lee R, Pavlin CJ, Ahmed IK. Evaluating the effect of slit-lamp illumination on gonioscopy using anterior segment optical coherence tomography (AS-OCT). Paper presented at: The 3rd International Congress on Glaucoma Surgery; May 26, 2006; Toronto, Canada.
