Surgical management of glaucoma

Surgical highlights from the American Glaucoma Society’s annual meeting included the initial reporting of results from the Tube versus Trabeculectomy (TVT) study and a description of a novel technique known as canaloplasty.

The TVT Study

Steven J. Gedde, MD, and Leon W. Herndon, MD, announced at the American Glaucoma Society meeting for the first time the 1-year results of the TVT study.¹ In this multicenter trial, 212 patients (ages 18 years to 85 years; mean age 71 years) with a history of previous trabeculectomy, cataract extraction and/or IOL implantation and an IOP >18 mm Hg and < 40 mm Hg (mean IOP 25 mm Hg) were randomized to undergo placement of a 350-mm ² Baerveldt glaucoma implant (n=107) or trabeculectomy with mitomycin C (n=105) 0.4 mg/mL for 4 minutes.

Although the incidence of intraoperative complications was similar between groups, trabeculectomy was associated with a significantly higher incidence of postoperative complications compared with tube shunt surgery.
—Leon W. Herndon, MD

IOP was significantly lower during the first 3 months in the trabeculectomy group compared with the tube group; however, there were no significant differences between the groups after 6 months and 1 year. Treatment failure was defined as IOP >21 mm Hg, failure to achieve 20% IOP reduction by 3 months, loss of light perception or need for repeat glaucoma surgery. The failure rate was significantly higher in the trabeculectomy group compared with the tube group (13.5% vs 3.9%). More qualified successes occurred in the tube group, but more complete successes occurred in the trabeculectomy group, consistent with the greater need for medical therapy in the tube group. Additional glaucoma surgery was needed in one patient in the tube group compared with six patients in the trabeculectomy group (P=.045). The researchers proposed that these efficacy data should be interpreted in light of the associated surgical complications, which were higher in the trabeculectomy group.

Leon W. Herndon, MD, and colleagues discussed the intraoperative and postoperative complications for both groups.³ No significant differences existed between the tube and trabeculectomy groups with respect to the incidence of intraoperative complications (7 patients vs. 10 patients; P=.59). Postoperative complications occurred in 36 patients in the tube group and in 60 patients in the trabeculectomy group (P=.001) and included choroidal effusion (17 vs. 20 patients), shallow or flat anterior chamber (12 vs. 10), wound leak (one vs. 12), hyphema (two vs. eight) or persistent corneal edema (seven vs. three). Eight patients in the tube group and five patients in the trabeculectomy group required reoperation for complications (P=.51), a difference that was not significant. Multivariate analysis demonstrated that anterior chamber shallowing was the only surgical complication that independently predicted cataract progression. Wound leak and hypotony maculopathy were independently predictive of treatment failure. Patients with persistent corneal edema and choroidal effusion were more likely to experience a decline in vision. Although the incidence of intraoperative complications was similar between groups, trabeculectomy was associated with a significantly higher incidence of postoperative complications compared with tube shunt surgery. Patients with postoperative complications experienced greater vision loss than patients without complications.

Canaloplasty

Specific treatment of the canal to restore natural outflow of aqueous is a viable and safe means of treating patients with glaucoma.
—Richard A. Lewis, MD

Richard A. Lewis, MD, described a novel technique of cannulating Schlemm’s canal using a fiberoptic flexible microcatheter and then applying a prolene suture to place tension on the canal.⁴ This technique referred to as canaloplasty involved the creation of a scleral flap followed by a second internal flap to gain access into the canal. The canal was then intubated with a cannula (Surgical Ophthalmic Microcannula, iScience) that had a lighted beacon and the ability to infuse viscoelastic (Healon GV, Advanced Medical Optics) to facilitate the passage. The microcatheter was used to pull a prolene suture into the entire circumference of the canal and the ends were tied to provide tension to the trabecular meshwork. The flap was tied tightly to avoid bleb formation. Dr. Lewis presented results from an ongoing multicenter study. To date, 133 patients (aged 43 to 89 years) with POAG and IOP >21 mm Hg have been enrolled in the study. Exclusion criteria included the presence of angle closure or secondary glaucoma or a history of more than one laser trabeculoplasty, postoperative bleb or previous surgery in or around Schlemm’s canal. Ninety-nine patients had the suture successfully placed. These patients had a mean preoperative IOP of 23.3 mm Hg and were taking a mean 2.1 medications. Data were available on 20 of the 99 patients at the 6-month follow-up visit. The mean IOP decreased to 13.7 mm Hg and patients were taking a mean 0.2 medications. Adverse events associated with the procedure included hyphema (the most common), hypotony (n=1), Descemet membrane tear, irregular pupil and transient elevated IOP. One patient required follow-up trabeculectomy. In addition to these primary clinical end points, Dr. Lewis shared a number of observations with the audience. Overall, IOP tended to stabilize in 6 to 8 weeks following the procedure. The extent of the IOP lowering depended on the degree of suture tensioning, which was quantitatively determined by the amount of “tenting” of the scleral spur as measured by postoperative high-resolution ultrasound. The amount of viscoelastic injected into the eye was critical and the tension of the canal suture was an important component that determined the efficacy of the procedure. Some limitations of the study were that no control group was present, a learning curve existed from the standpoint of the study as well as from the investigators learning the technique, patient variability and the undetermined role of drug therapy. Other critical variables included the amount of viscoelastic injected into the eye and the tension of the canal suture. However, the overall results of the study show that understanding and controlling the outflow system are the keys to treating glaucoma. Canaloplasty is a nonpenetrating approach to glaucoma surgery that utilizes circumferential flow of the canal of Schlemm into the outflow system. The role of postoperative medications and what happens to the suture of the canal are areas for future research.

References

Gedde SJ, Schiffman JC, Feuer WJ, Parrish RK, Heuer DK, Brandt JD. The tube versus trabeculectomy study: Design and baseline characteristics of study patients. Am J Ophthalmol. 2005;140(2):275-287.
Gedde SJ, Schiffman JC, Feuer WJ, Herndon LW, Brandt JD, Budenz DL. Treatment outcomes in the Tube Versus Trabeculectomy (TVT) study after one year of follow-up. Paper presented at: Annual Meeting of the American Glaucoma Society; March 3, 2006; Charleston, SC.
Herndon LW, Gedde SJ, Brandt JD, Budenz DL, Schiffman JC, Feuer WJ. Surgical complications in the Tube Versus Trabeculectomy (TVT) Study during the first year of follow-up. Paper presented at: Annual Meeting of the American Glaucoma Society; March 3, 2006; Charleston, SC.
Lewis RA, Fellman R, Kearney J, Ball S, Stegman R, Tetz M. Canaloplasty: Enhancing circumferential outflow using a flexible micro-catheter in schlemm’s canal in POAG patients: Interim results from a multi-center clinical trial. Paper presented at: Annual Meeting of the American Glaucoma Society; March 3, 2006; Charleston, SC.