Excimer laser trabeculostomy (ELT) reestablishes physiologic aqueous outflow through endogenous drainage pathways without creating an external filtration bleb. The procedure involves fiber-optically delivering a 308-nm excimer laser light across the anterior chamber through a limbal paracentesis in order to connect the anterior chamber with the canal of Schlemm, thereby reducing outflow resistance and decreasing IOP. This article describes this promising, new, minimally invasive glaucoma surgery and highlights clinical data verifying its efficacy at lowering IOP, especially in combination with cataract surgery.
Glaucoma Therapies
Today, medications are often the first line of glaucoma therapy, but they are associated with adverse, sometimes severe side effects.4 In addition, medication regimens may change due to tachyphylaxis and the availability of newer drugs. The costs of medical glaucoma control over a lifetime can also be prohibitive for some patients, a fact that creates a need for safe and effective surgical interventions. After medication use, the most common glaucoma treatments today are argon laser trabeculoplasty (ALT), selective laser trabeculoplasty (SLT), and manual filtering surgical procedures such as trabeculectomy. ALT and SLT increase conventional aqueous outflow through the trabecular meshwork,5 but these procedures have limited efficacy and duration of effect. Complications of trabeculectomy include hypotony, a shallow or flat anterior chamber with or without choroidal effusion, suprachoroidal hemorrhage, hyphema, and, most commonly, eventual failure as the filtering bleb heals itself.6 Patients often find the external conjunctival bleb to be uncomfortable, and it can become thin and avascular, thereby increasing the risk of bleb leaks and endophthalmitis.7 Trabeculectomy tends to be less successful in young eyes and in eyes that produce large amounts of scar tissue. In the case of failed filtration surgery, repeated operations may be necessary, but the chances for success decrease as the sclera and conjunctiva are subjected to repeated surgical insults.
Another IOP-lowering procedure involves placing a glaucoma drainage device (tube shunt) such as the Molteno Implant (Molteno Ophthalmic Limited, Dunedin, New Zealand), Baerveldt shunt (Pfizer Inc., New York, NY), Krupin Eye Valve (Hood Laboratories, Pembroke, MA), and Ahmed Glaucoma Valve (New World Medical, Rancho Cucamonga, CA).8,9 The surgeon places the tube into the anterior chamber and secures a space-maintaining plate in the sub-Tenon's space. Shunts have a relatively high success rate, but the nature of their designs and placement technique puts the patient at a greater risk for complications than do nonimplant surgeries such as trabeculectomy.10
ELT Technique
The concept of treating the pathology of most open-angle glaucoma via outflow obstruction at the juxtacanalicular trabecular meshwork is well established. To be successful, however, a procedure to bypass this obstruction must be accurate and stealthy, producing little or no healing response. Excimer laser-tissue interactions fulfill both requirements. Because the 308-nm wavelength allows the removal of trabecular meshwork by photoablation without inducing thermal damage, it minimizes the healing response and scar formation. ELT reestablishes physiologic aqueous outflow through endogenous drainage pathways without creating an external filtration bleb. The surgeon excises a defined area of the trabecular meshwork and juxtacanalicular tissue. The laser removes tissue while producing minimal thermal mechanical damage to the surrounding tissue, thereby reducing postlaser healing responses. ELT increases aqueous outflow into the canal of Schlemm and thereby lowers IOP.11-14
In ELT, the surgeon makes a paracentesis incision and stabilizes the anterior chamber with a viscoelastic. The laser is passed across the anterior chamber via the paracentesis incision and toward the opposite chamber angle to contact the trabecular meshwork. The surgeon applies laser energy (AIDA Excimer Laser System; TuiLaser AG, Germering, Germany) directly to the trabecular meshwork by means of a fiber-optic delivery system (LAGO 200 or LAGO 200 ENDO; TuiLaser AG), which traverses the anterior chamber via a paracentesis incision (Figure 1).
Figure 1. This schematic diagram of ELT shows how the fiber-optic approaches the trabecular meshwork across the anterior chamber.
Currently, ELT involves creating about 10 laser excisions (trabeculostomies) distributed over approximately 90ยบ. The surgeon monitors the fiber position either with a goniolens or an endoscope. Figure 2 shows an endoscopic view demonstrating the fiber-optic delivery of laser energy to the trabecular meshwork. Figure 3 shows the first trabeculostomy after creation. In Figure 4, Dr. Funk has created the second trabeculostomy, and retrograde blood is visible at the site of the first trabeculostomy.
Figure 2. In this endoscopic view, the fiber-optic delivery approaches the trabecular meshwork.
Figure 3. This endoscopic view shows the first trabeculostomy after its creation.
Figure 4. In this endoscopic view, retrograde bleeding occurs at the site of the first trabeculostomy when a second is created.
COMBINING CATARACT SURGERY WITH ELT
Cataract excision often decreases patients' IOPs. Combining ELT with cataract surgery can further lower IOP and has proven effective clinically for more than 30 months.15 In contrast, combining clear corneal cataract surgery and filtering glaucoma surgery (ie, trabeculectomy) has been less successful than when the procedures occur at two different time points.16 When combined with cataract surgery, ELT is performed through the same corneal incisions with only a minimum of additional time.
Clinical studies have consistently demonstrated a significant IOP reduction after ELT11 to levels in the midteens. Reducing IOP to approximately episcleral venous pressure has been shown to effectively stabilize glaucoma.15,17-20 Figure 5 shows pooled data of combined ELT and cataract surgeries by five surgeons in four German eye clinics. The combined procedures effectively decreased IOP as well as the average number of medications that the patients were taking.
Figure 5. Pooled data from several surgeons show a reduction in IOP versus time after combined ELT and cataract surgery.18
COMPARING ELT, COMBINED SURGERY, AND THE EFFECT OF DIFFERENT POSTOPERATIVE MEDICATIONS
Methodology
Drs. Giers and Kleineberg are collaborating with Lutz Pillunat, MD, of the University of Dresden in Germany on a study in Detmold, Germany. Its purpose is to compare the IOP-lowering effect of ELT as a stand-alone procedure versus a combined procedure with cataract surgery. The investigators also are comparing the effect of different postoperative medications after otherwise identical surgeries. The study is evaluating three groups: ELT alone with postoperative steroids t.i.d. for 10 days (group 1, N=22); ELT alone with postoperative nonsteroidal anti-inflammatory drugs (NSAIDs) t.i.d. for 10 days (group 2, N=15); and combined ELT/cataract surgery with postoperative steroids t.i.d. for 28 days (group 3, N=23).
All subjects are older than 18 years. They had open anterior chamber angles (Shaffer III-IV), an initial IOP of less than 40 mm Hg, and either primary open-angle glaucoma or secondary open-angle glaucoma (such as pseudoexfoliation). The indications for surgery were an increased IOP under maximum tolerated medical therapy, progressive glaucomatous damage under maximum tolerated therapy, allergies to medication, and noncompliance with medical therapy. The exclusion criteria were a narrow anterior chamber angle (Shaffer I-II), neovascularization of the iris, an abnormal iris configuration, and dysplasia of the trabecular meshwork. Postoperative follow-up has occurred 1 day, 8 days, 4 weeks, 3 months, and 6 months after the operation. The investigators are monitoring subjects' IOPs, visual fields, visual acuities, and imaging results with the GDx VCC (Laser Diagnostic Technologies, San Diego, CA).
Results
The average IOP reduction 6 months after surgery in group 1 was 34%. Five of 22 patients have had to remain on antiglaucomatous medication. The visual field results improved in five of 22 patients, deteriorated in one, and remained unchanged in 16. Three patients responded to steroids and underwent treatment with NSAIDs instead. Two suffered allergic reactions to postoperative medication.
Subjects in group 2 also experienced an average IOP reduction of 34% 6 months after surgery. Four out of 15 patients have had to remain on antiglaucomatous medication, although all at lower amounts than before ELT. Visual field results improved in one patient and remained unchanged in 14. One patient developed conjunctivitis and required treatment with an additional topical steroid.
In group 3, subjects experienced an average 42% reduction in IOP 6 months after surgery. Four of 23 patients have had to remain on antiglaucomatous medication, although at lower amounts than before surgery. Visual field measurements improved in five of 23 patients, remained unchanged in 17, and deteriorated in one. Six of 20 patients responded to steroids and were treated with NSAIDs instead. One patient developed conjunctivitis and received treatment with a topical combination steroid-antibiotic q2h.
Figure 6 shows the average IOP for all groups 6 months postoperatively (the study continues to monitor longer periods). These results demonstrate that the IOP reduction is greatest when ELT is combined with cataract surgery.
Figure 6. In this graph of IOP reduction by ELT, the error bars designate maximum and minimum measurements in groups 1 through 3.
CONCLUSION
No serious complication of ELT has been reported after hundreds of procedures at multiple centers. ELT creates no filtering bleb or hypotony, and it leaves the conjunctiva intact. Prior surgery does not constitute a contraindication, but we anticipate that procedures that compromise distant outflow channels (such as extensive ALT) may also compromise the efficacy of ELT.
This promising, new, minimally invasive glaucoma surgery is particularly effective in lowering IOP when combined with cataract surgery. Techniques and protocols are evolving, and controlled clinical trials are in progress.21 Clinical data to date confirm ELT's safety and its efficacy at lowering IOP.
Iqbal Ike Ahmed, MD, FRCSC, is employed by the University of Toronto in Canada. He disclosed no financial interest in the technologies, products, and companies mentioned herein. Dr. Ahmed may be reached at (905) 459-0088; ike.ahmed@utoronto.ca.
Michael S. Berlin, MD, is Professor of Ophthalmology at the Jules Stein Eye Institute, University of California, Los Angeles. US patent 4,846,172 was issued to Dr. Berlin, but he disclosed no other financial interest in the technologies, products, and companies mentioned herein. Dr. Berlin may be reached at (310) 855-1112; berlin@ucla.edu.
Jens Funk, MD, PhD, is employed by the University Eye Clinic in Freiburg, Germany. He disclosed no financial interest in the technologies, products, and companies mentioned herein. Dr. Funk may be reached at +49 761 270 4046; funk@aug.ukl.uni-freiburg.de.
Ulrich Giers, MD, is employed by the Praxisklinik Elisabethstr in Detmold, Germany. He disclosed no financial interest in the technologies, products, and companies mentioned herein. Dr. Giers may be reached at +49 5231 3090 0; ugiers@doc4eye.de.
Lea Kleineberg, MD, is employed by the Praxisklinik Elisabethstr in Detmold, Germany. She disclosed no financial interest in the technologies, products, and companies mentioned herein. Dr. Kleineberg may be reached at +49 5231 3090 0; lea.kleineberg@htp-tel.de.
Mona Pache, MD, is employed by the University Eye Clinic in Freiburg, Germany. She disclosed no financial interest in the technologies, products, and companies mentioned herein. Dr. Pache may be reached at +49 761 270 4001; pache@aug.ukl.uni-freiburg.de.
Sonja Wilmsmeyer, MD, is employed by the University Eye Clinic in Freiburg, Germany. She disclosed no financial interest in the technologies, products, and companies mentioned herein. Dr. Wilmsmeyer may be reached at +49 761 270 4092; wilmsmeyer@aug.ukl.uni-freiburg.de.
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