I completed my glaucoma fellowship in 1991, and have devoted my academic and clinical career to glaucoma for the past 20 years. These years of experience have led me to ask the question: is the old trabeculectomy procedure I learned as a resident still the glaucoma surgeon's best surgical option? The purpose of glaucoma surgery is to control IOP so that we may preserve patients' visual function and ultimately maintain their quality of life. IOP control is the endpoint by which glaucoma surgery is measured, but it is equally important that the glaucoma surgery not create any avoidable complications. This article reviews the benefits and drawbacks of trabeculectomy versus other procedures to control IOP.
THE PROS AND CONS OF TRABECULECTOMY
Trabeculectomy has not changed much in the past 20 years, although each small change has improved its success or decreased complications. Other than slight differences in flap construction, anti-scarring strategies, or wound closure, the procedure still entails diverting aqueous from the anterior chamber to the subconjunctival space and hoping for sufficient but not excessive resistance to outflow. We continue to perform trabeculectomy because we believe it is effective at lowering IOP, although the Tube Versus Trabeculectomy study1 suggests that perhaps the procedure is not as effective in the long run as we would like to believe.
The drawbacks of trabeculectomy are that its efficacy is unpredictable, and there are too many complications. Patients' postoperative IOP can be too low or too high. Their wound-healing response can be modulated, but not always sufficiently. Also, the procedure requires intensive postoperative care to achieve a favorable result. I tell my patients that half the work of trabeculectomy is done in the OR, and the other half is done postoperatively, when we identify the pattern of healing and adjust our interventions accordingly. My daily patient schedule is filled with post-trabeculectomy visits. Although we glaucoma surgeons have done our best over the years to modify the technique to minimize complications, I think we have to question the long-term success of this procedure. Only a few studies have looked at the 3- and 5-year success rates of trabeculectomy. The 5-FU Filtering Surgery study2 showed a 50% rate of failure at 5 years—the same as in the Tube Versus Trabeculectomy study.
CONSIDERATIONS FOR TRABECULECTOMY SURGERY
Prior to performing trabeculectomy, we must identify the surgical risk factors and plan our surgical approach in the office, rather than on the table in the OR. Intraoperatively, I feel that certain strategies have significantly improved my surgical efficiency and reduced my intraoperative and early postoperative complications. For example, after I switched to using topical anesthesia, I no longer struggled with bleeding or hydration in the conjunctiva or Tenon's capsule. Switching to an incision at the limbus (fornix-based) improved my exposure and reduced the need for a skilled assistant.
A modification of the trabeculectomy procedure is to use a short tube under the scleral flap rather than create an ostium in the sclera or peripheral cornea. One such device that can be implanted under a scleral flap is the EX-PRESS Glaucoma Filtration Device (Alcon Laboratories, Inc., Fort Worth, TX; Figure 1). This device has been available for several years, and we continue to gain experience with it. In one prospective study, de Jong randomized 78 glaucomatous patients to receive either the EX-PRESS device or trabeculectomy.3 Although the mean IOP was statistically the same between the two groups, there was a greater rate of success (defined as an IOP of less than or equal to 18 mm Hg) in the patients who received the EX-PRESS device at 1 year follow-up.
At best, trabeculectomy results in desired long-term control of IOP, but the patient will have a bleb for the rest of his or her lifetime, which entails a 1% risk per year of endophthalmitis (Figure 2). It is trabeculectomy's unpredictability and the risk of complications and infection that has led practitioners to seek alternative approaches to lowering IOP surgically.
AQUEOUS-DIVERSION STRATEGIES TO CONTROL IOP
Tubes
Aqueous humor serves a purpose in the eye, and the reduction of IOP by aqueous diversion is more physiologic that aqueous suppression. There are only a few convenient spaces to which we can divert aqueous flow: the conventional outflow pathway, the subconjunctival space, and the uveoscleral space. The subconjunctival space can be accessed via trabeculectomy or tubes: long tubes; short, full-thickness, transscleral tubes (no longer advocated); or short tubes under a scleral flap. In my opinion, the biggest advance in our understanding of diverting aqueous to the subconjunctival space was the thoughtful, prospective study of tubes versus trabeculectomy conducted by Stephen Gedde, MD, and colleagues that has reported 3- year results.1 In the study, more than 200 patients were randomized to undergo either trabeculectomy with mitomycin C or to receive a Baerveldt implant (Abbott Medical Optics Inc., Santa Ana, CA). While there are always limitations to generalizing from clinical trials, these investigators reported that tube shunt surgery had a higher success rate than trabeculectomy with MMC during the first 3 years of follow-up; the failure rate was greater in the trabeculectomy group than in the tube group.
Accessing the Conventional Outflow Pathway
Procedures designed to increase the aqueous' access to the conventional outflow pathways are available. Canaloplasty (iScience Interventional, Menlo Park, CA), as it is now performed by most surgeons, involves passing a device around the full circumference of Schlemm's canal and using it to place a suture within the canal that is then tied under tension. This procedure is performed under a scleral flap. Canaloplasty preserves the trabecular meshwork and works either through improving transmeshwork flow, distal flow, or both. Because canaloplasty has been performed in eyes with and without cataracts, it is somewhat challenging to analyze data on this technique. Although no prospective, randomized studies have examined this procedure, the canaloplasty study for open-angle glaucoma by Lewis et al now has 3-year data,4 and it reported IOP-lowering efficacy in the study population. Also, some surgeons are taking the approach of converting canaloplasty to a filtering procedure with goniopuncture, either when IOP lowering is not sufficient or as a planned, staged procedure.
Another approach is ablation of the trabecular meshwork (the Trabectome [NeoMedix, Inc., Tustin, CA]), to decrease outflow resistance. This is often performed in combination with another procedure such as cataract surgery. The Trabectome (Figure 3) is a new way to achieve anatomically what we do with goniotomy, albeit the former is an advancement in that it incises and also ablates tissue. An informal poll of audience members at the recent AGS meeting in Dana Point, California, found that nearly half had access to this technology.
A similar strategy is to bypass the trabecular meshwork by placing an unrestricted stent (the iStent [Glaukos Corp., Laguna Hills, CA; not available in the United States]) from the anterior chamber through the trabecular meshwork and into Schlemm's canal (Figure 4). Thomas Samuelson, MD, has published the results of a randomized evaluation of the iStent implanted after cataract surgery.5 He found an incremental improvement in the number of patients who achieved a successful endpoint, although the cataract surgery lowered the IOP in at least 50% of the eyes. Again, it is challenging to judge the effects of procedures that are done in conjunction with other surgeries that also lower IOP.
Uveoscleral outflow is the physiologic diversion of aqueous to the suprachoroidal space. Choroidal detachment is pathologic. However, any physiologic pathway we create should be accessible. In the past, glaucoma surgeons used cyclodialysis, a very effective IOP-lowering procedure, although it was unpredictable and has largely been abandoned. In a proof-of-concept study published in the Journal of Glaucoma,6 some end-stage glaucomatous eyes were implanted with a silicone tube that ran from the anterior chamber into the suprachoroidal space. This procedure effectively lowered IOP and had a fairly low complication rate. Since then, investigational shunts have been developed to access this space, such as the Solx Gold shunt (Solx, Inc., Waltham, MA; not available in the United States) and the CyPass implant (Transcend Medical, Inc., Menlo Park, CA; not available in the United States; Figure 5). Again, these devices do not yet have prospective, randomized studies to support their efficacy, but this area of the eye is interesting to consider as a potential target for aqueous diversion.
CONCLUSIONS
Is trabeculectomy still our best surgical option? I believe it is for some eyes. Most busy glaucoma surgeons still perform this procedure, although our acceptance of new approaches is growing. As alternatives emerge, we have the option to consider which procedure best fits the clinical situation for each patient. The quality of the study designs and the reporting surrounding these newer procedures varies considerably, however, and we would be well served if surgical clinical trial reports were modeled on the World Glaucoma Association's guidelines on reporting surgical study results.7 Better-designed studies will help us continue to understand whether alternative surgical methods of controlling IOP are safer and more predictable than trabeculectomy.
Robert D. Fechtner, MD, is the director of the Glaucoma Division at the University of Medicine and Dentistry in New Jersey, and he is a professor of ophthalmology at the Institute of Ophthalmology, both at New Jersey Medical School in Newark. He is a consultant to and has received research support from Alcon Laboratories, Inc., and Allergan, Inc. Dr. Fechtner may be reached at (973) 972-2030; ,fechtner@umdnj.edu.
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