THE AHMED VERSUS BAERVELDT STUDY ONE-YEAR TREATMENT OUTCOMES
Christakis PG, Kalenak JW, Zurakowski D, et al*
Ophthalmology, September 2011
This or That
Among other reasons, the field of glaucoma is particularly
fascinating because many debates within the specialty
remain unsettled. Is glaucomatous optic neuropathy
caused by mechanical or ischemic stress? Should glaucoma
initially be treated with laser therapy, medications, or
surgery? Is tube implantation better than trabeculectomy?
Which tube is better, the Ahmed Glaucoma Valve
(New World Medical, Inc., Rancho Cucamonga, CA) or
Baerveldt glaucoma implant (Abbott Medical Optics Inc.,
Santa Ana, CA). Prospective randomized multicenter
clinical trials have been helpful in addressing these classic
debates.
We glaucoma specialists learned that initial treatment with laser trabeculoplasty is at least as efficacious as treatment with topical medications,1 and medication seems to preserve the visual field as well as trabeculectomy, even if this surgery achieves a lower IOP.2 Even the tube versus trabeculectomy debate has been addressed, with 3-year data from the Tube Versus Trabeculectomy (TVT) Study's demonstrating a higher failure rate in trabeculectomy with mitomycin C (31%) compared to a 350 mm2 Baerveldt glaucoma implant (15%). This outcome was also evident when both treatments were associated with rather high complication rates (60% and 39%, respectively).3
The publication of the 1-year treatment outcomes from the Ahmed Versus Baerveldt (AVB) Study will help surgeons decide which tube shunt to implant.4 In an international, randomized trial performed by 10 surgeons at seven international sites, 238 patients with inadequately controlled glaucoma refractory to conventional medicinal, laser, and surgical therapy were randomized to receive an Ahmed FP7 (n = 124) or Baerveldt-350 (n = 114). Failure was defined as an IOP reduction of less than 20% from baseline or an IOP of more than 18 mm Hg or less than 5 mm Hg at two consecutive visits occurring past the 3-month postoperative mark. Patients enrolled in the study had a baseline IOP of 31.4 mm Hg and were, on average, taking three glaucoma medications, with 37% having undergone a previous trabeculectomy. Roughly half of the patients had open-angle glaucoma, 21% had neovascular glaucoma, and 10% had uveitic glaucoma. As could be expected, the early postoperative IOPs were lower in the first month with the Ahmed versus the Baerveldt implant, but this difference disappeared by 1 month. After 1 year, the mean IOP was 16.5 mm Hg (47% reduction from baseline) in the Ahmed group and 13.8 mm Hg (57% reduction from baseline) in the Baerveldt group (P = .001), with slightly fewer glaucoma medications required in the Baerveldt group compared to the Ahmed group (1.2 vs 1.6, P = .03). Kaplan-Meier survival plots demonstrated that a higher proportion of patients in the Baerveldt group survived at 1 year compared to the Ahmed group when using the primary criteria (IOP of 5-18 mm Hg) but not using less stringent criteria (IOP 5-21 mm Hg). Most failures occurred due to high IOP, and only one patient (Baerveldt, of course) developed persistent hypotony. Visual acuity was similar between the two groups at 1 year. As with most prospective studies where the investigators are actually looking for and documenting all adverse events, complication rates were high in the two groups (45% for Ahmed, 54% for Baerveldt; P = .19), and more patients in the Baerveldt group required intervention for these complications (26% Ahmed vs 42% Baerveldt; P = .009). In general, the interventions themselves were modest and mostly included anterior chamber reformation, anterior chamber paracentesis, and bleb needling. A few more substantial interventions were required, including cataract extraction, vitrectomy, and tube revision.
Will the results of the AVB study change clinical practice? For the answer to this question, we can consider other randomized clinical trials such as the Advanced Glaucoma Intervention Study (AGIS), the Collaborative Initial Glaucoma Treatment Study (CIGTS), and the Glaucoma Laser Trial (GLT) and how they have not influenced practice. Before attributing the rise in the popularity of tube shunt surgery to the TVT study, we should remember that this trend occurred prior to the publication of the study's results. In some cases, we may be hesitant to make clinical changes based on the results of a study, because we feel the inclusion criteria, study protocol, patient population, surgical technique, or duration of follow-up are not what we would desire in order to make an informed decision for our patients. For many of us who use both glaucoma drainage devices, the clinical scenario (eg, degree of preoperative IOP elevation or disease stage) may determine which device we implant, and the AVB study cannot provide specific guidance in this arena. Finally, as Joseph Caprioli, MD, said in a thoughtful editorial on the results of the TVT study, “The sheer inertia of longestablished clinical practice is often difficult to change.”5
*Financial disclosures: the authors stated that they hold no proprietary interest in the materials discussed herein.
INCIDENCE OF, RISK FACTORS FOR, AND COMBINED MECHANISM OF LATE-ONSET OPEN-ANGLE GLAUCOMA AFTER VITRECTOMY.
Koreen L, Yoshida N, Escario P, et al*
Retina, July 2011
Is Pars Plana Vitrectomy Associated With Primary
Open-Angle Glaucoma?
In his 2006 LXII Edward Jackson lecture titled “Open-
Angle Glaucoma After Vitrectomy,” Stanley Chang, MD,
proposed that there is an increased risk of open-angle
glaucoma after vitrectomy.6 In an article recently published
in Retina, Dr. Chang and colleagues revisited this
issue using a retrospective cohort and matched casecontrolled
study design for 285 vitrectomized eyes.7
They found that 11.6% (n = 33) developed glaucoma
within 6 months of vitrectomy. The only variable significantly
associated with the development of glaucoma was
cataract extraction, whether it had been performed prior to or
during the vitrectomy (odds ratio = 16.4; 95% confidence interval,
2.1-127.4; P = .007). For phakic eyes, the incidence of glaucoma
was low at 1.4%, and the incidence in nonphakic eyes was
15%. The authors concluded that patients with lens extraction
prior to or during vitrectomy surgery should be carefully monitored
for the development of open-angle glaucoma. This work
suggests that a discussion of the risks of glaucomatous development
should be a part of the informed consent process for
some patients requiring vitrectomy.
*Financial disclosures: the authors stated that they hold no proprietary interest in the materials discussed herein.
LOWER CORNEAL HYSTERESIS IS ASSOCIATED WITH MORE RAPID GLAUCOMATOUS VISUAL FIELD PROGRESSION
De Moraes CG, Hill V, Tello C, et al*
Journal of Glaucoma, June 2011
Corneal Thickness or Hysteresis?
Despite some continued controversy on the subject, a
lower central corneal thickness (CCT) has been independently
associated with the onset and progression of glaucoma.
8-10 In 2006, Nathan Congdon, MD, MPH, and colleagues
reported that a measure of corneal stiffness
(corneal hysteresis) was associated with visual field progression
and that CCT was not, although CCT was associated
with the structural state of glaucomatous damage
(cup-to-disc ratio).11 De Moraes and colleagues recently
revisited the issue by evaluating factors associated with
visual field progression in 153 patients who had taken
more than five visual field tests (mean, 8.5) over an average
of 5 years of follow-up.12 The investigators found that 16%
of progressing eyes had lower corneal thickness (525.0 ±34.2 μm vs 542.3 ±38.5 μm, P = .04) and lower hysteresis
(7.5 ±1.4 mm Hg vs 9.0 ±1.8 mm Hg, P < .01) compared
to nonprogressing eyes. In a multivariable analysis, peak
IOP, age, and corneal hysteresis (but not thickness) were
significantly associated with progression. This study provides
a strong rationale for the investigation of corneal
hysteresis in prospective studies of glaucomatous progression.
Furthermore, it suggests that, in the future, we
may depend on corneal biomechanical properties to
help guide our therapeutic decisions.
*Financial disclosures: the authors stated that they hold no proprietary interest in the materials discussed herein.
CANALOPLASTY: THREE-YEAR RESULTS OF CIRCUMFERENTIAL VISCODILATION AND TENSIONING OF SCHLEMM CANAL USING A MICROCATHETER TO TREAT OPEN-ANGLE GLAUCOMA.
Lewis RA, von Wolf K, Tetz M, et al*
Journal of Cataract and Refractive Surgery, April 2011
Three-Year Data for Canaloplasty
Lewis and colleagues reported 3-year safety and efficacy data for 157 patients who underwent either canaloplasty or combined cataract extraction and canaloplasty.13 In the canaloplasty procedure, after the creation of a scleral flap, the surgeon used a flexible microcatheter through an ab externo (transconjunctival, transscleral) approach to viscodilate the full circumference of Schlemm canal and placed a 10–0 Prolene trabecular-tensioning suture (Ethicon Inc., Somerville, NJ). At 3 years, the overall mean IOP fell to 15.2 ±3.5 mm Hg from a mean preoperative IOP of 23.8 mm Hg, and the mean use of glaucoma medication fell to 0.8 ±0.9 compared with 1.8 ±0.9 medications preoperatively. These figures correspond to an 8.6-mm Hg or 36% reduction from baseline. The mean IOP of eyes that underwent both cataract and canaloplasty surgery fell to 13.6 ±3.6 mm Hg, and the number of medications needed postoperatively decreased to 0.3 ±0.5. In this group, the mean baseline IOP was 23.5 ±5.2 mm Hg on 1.5 ±1.0 medications (42% IOP reduction). The only significant complications reported were cataract formation in 12.7% of eyes and a transient elevation in IOP in 6.4% of eyes.
The results are encouraging. Although it may not be valid to compare one surgical population's outcome to that of another study, the percentage of IOP reduction and safety profile obtained compare well with those of other surgical trials.14 This noncomparative series certainly provides a rationale for a head-to-head comparison of canaloplasty and more traditional penetrating glaucoma surgeries.
*Financial disclosures: the authors stated that they hold no proprietary interest in the materials discussed herein.
Section Editor James C. Tsai, MD, is the chairman and Robert R. Young professor of ophthalmology and visual science at Yale University School of Medicine in New Haven, Connecticut. He acknowledged no financial interest in the products or companies mentioned herein. Dr. Tsai may be reached at (203) 785-7233; james.tsai@yale.edu.
Nathan M. Radcliffe, MD, is an assistant professor of ophthalmology at Weill Cornell Medical College, New York-Presbyterian Hospital, New York. He acknowledged no financial interest in the products or companies mentioned herein. Dr. Radcliffe may be reached at (646) 962-2020; drradcliffe@gmail.com.
