The Tube Versus Trabeculectomy (TVT) study1 published last year brought glaucoma tube devices back into the forefront of surgical discourse. The well-designed, prospective study conducted by Steve Gedde, MD, and colleagues in Boston randomized 212 glaucomatous patients to receive either a Baerveldt 350-mm glaucoma implant (n=107) or to undergo trabeculectomy with wound management (n=105). The results of this study caused the investigators to conclude that the implant was a more effective procedure than trabeculectomy with a lower incidence of complications in patients who had already undergone some type of previous surgery. These findings raised the question: is trabeculectomy still a viable option, or does the glaucoma implant change our standard of care? Let's consider the data carefully and then examine the appropriate answer.
TVT TRIAL OUTCOMES
Success and Failure
I believe that glaucoma tubes are valuable for eyes
that have undergone previous surgery, but their value
may be overstated in terms of a routine glaucoma filtering
surgery. The device implant group in the TVT trial
experienced a 15% failure rate at 3 years, compared with
a 30% failure rate in the trabeculectomy group. However,
although most of the eyes in the trabeculectomy
group were good candidates for a tube device, the failed
trabeculectomy eyes were not ideal candidates for a trabeculectomy.
Thus, half of the eyes had already failed
one arm of the study prior to surgery. The definition of
success in the TVT trial at 3 years was an IOP of less
than 21 mm Hg and reduced by 20% with no medications.
Forty percent of the trabeculectomy patients met
this definition of success, compared with only 28% of
the tube device patients. Therefore, medications played
a significant role in these patients' eventual success. The
rate of late and serious complications was similar for
both groups, but the trabeculectomy procedure was
blamed for a greater number of early complications (60
versus 36 in the device group). Twelve of those 60 complications
were wound leaks, and eight were hyphemas.
The device group experienced three intraoperative scleral
perforations—something I do not consider insignificant.
IOP and Visual Acuity
Although both groups in the TVT study experienced significantly
reduced IOP, a truly effective reduction of IOP to
14 mm Hg was achieved in only 58% of the trabeculectomy
patients and 62% of the tube device patients at 3 years postoperatively.
There was no significant difference in the rate of
visual loss between the two procedures, but it was concerning
that one out of three patients in both groups lost 2 or
more lines of Snellan acuity. This result in itself attests to the
complexity of treating these challenging cases. In short, the
trabeculectomy was effective in 70% of patients and with
fewer medications than the tube device group. Furthermore,
a recent follow-up study to the TVT trial found new
motility problems in 10% of patients in the tube device
group (and none in the trabeculectomy group).2
General Issue of Safety With Devices
A study by Kim et al that was presented at ARVO in
2008 examined the loss of endothelial cells in patients
who have undergone Ahmed tube device surgery out to
24 months.3 The operated eyes had 15% mean cellular loss
at 12 months and 18.3% at 24 months versus 2.8% at
12 months and 4.2% at 24 months in the unoperated eyes.
Interestingly, the percentage of cell loss was much greater
in the superior temporal zone, where the tubes were
placed. These findings are important when considering the
long-term safety of glaucoma tubes. We must recognize
that some complications can occur beyond 3 years.
In summary, the results of the TVT study cast tube devices in a favorable light in patients who have undergone previous conjunctival surgery. I certainly consider using these devices in eyes that have conjunctival fibrosis or conditions unfavorable for trabeculectomy. The role of glaucoma drainage tube devices in clear corneal pseudophakic eyes and primary glaucoma surgery is not at all clear, in my opinion. A primary tube versus trabeculectomy study is currently underway in the hope of clarifying this issue.
CANALOPLASTY
The idea of nonpenetrating canal surgery has
received a lot of attention among glaucoma surgeons.
The 2-year results from uncontrolled studies conducted
by iScience Interventional (Menlo Park, CA) have
now been published.4 The series included 84 patients
with 2 years of follow-up, and it found a 30% mean
reduction in IOP (from 23.2 to 16.3 mm Hg). This procedure
is not always simple or predictable, however,
and the surgeons were unable to find the canal or complete
the implantation of the microcatheter in 15% of
the cases. If we broadly compared the results of the
canaloplasty trial with the Collaborative Initial
Glaucoma Treatment Study (CIGTS),5 trabeculectomy
has an impressive track record (Table 1). It appears that
trabeculectomy is still the gold standard for achieving
super-low IOP in primary glaucoma surgery.
THE EX-PRESS GLAUCOMA FILTRATION DEVICE
It is important to make the procedure in the OR as
smooth, precise, controlled, and predictable as possible,
and the idea of standardizing trabeculectomy to
achieve this goal has been discussed before. When I
first encountered the EX-PRESS Glaucoma Filtration
Device (Alcon Laboratories, Inc., Fort Worth, TX), I
wondered how it might help me better manage glaucomatous
eyes and if it could give me better control
intra- and postoperatively. A retrospective study published
by Peter Netland, MD, and his group6 induced
me to try the device in surgery. In a routine case with
the EX-PRESS Glaucoma Filtration Device, I dissect my
scleral flap in the usual manner (Figure 1). Depending
on the specific device, I use a 26- or 27-guage needle to
create the entry for insertion. Once I insert the device
(Figure 2), there is immediately more stability in the
anterior chamber, and the surgery feels more controlled.
In the OR, this stability makes suturing the flap
less hurried. The Netland study included 100 eyes, 50
implanted with the EX-PRESS Glaucoma Filtration
Device and 50 without. There was no difference in IOP
between the groups, but the eyes implanted with the EX-PRESS device experienced less hypotony and
choroidal effusion early in the postoperative period.
Also, one of the first things I noticed when I started
using this device was the dramatic reduction in early
postoperative hyphema, a finding that was also significant
in the Netland study.
Another surgical switch I made about a decade ago was to fornix-based flap surgery (see the video, “Closing the Fornix-based Conjunctival Flap” on Eyetube.net) in order to improve on bleb morphology by allowing for more diffuse wound management exposure and a more posterior diffuse bleb (Figure 3). A major criticism with the fornixbased flap approach was a purportedly greater likelihood of wound leaks compared with limbal-based flaps. I did not want to make the change unless I was convinced I could achieve an equally effective wound closure. A review of my results with a fornix-based conjunctival flap approach performed after 2001 versus my limbus-based flaps performed before 2001 revealed no difference in terms of wound leaks requiring repair. Thus, I feel that combining this technique with wound-management application and use of the EX-PRESS Glaucoma Filtration Device gives me reliable control and more reproducible and favorable results in filtering surgery.
Clinically, and in postmortem evaluation, the EX-PRESS device appears to be remarkably biocompatible; it shows minimal evidence of surrounding inflammatory reaction when compared to the Ahmed or Baerveldt plate. A postmortem study conducted by de Feo et al7 found no difference in the corneal endothelial cell count in the eye that had the EX-PRESS device compared with the unoperated eye. Furthermore, the device has been found safe for MRI procedures.8
CONCLUSION
When it comes to complications, any step forward is a
step in the right direction. Although I still believe the trabeculectomy
is the gold-standard procedure, as glaucoma
surgeons, we must continuously raise bar for safer and more
effective surgery with new approaches that enhance our current
techniques and produce more favorable outcomes.
Garry P. Condon, MD, is an associate professor of ophthalmology at Drexel University College of Medicine in Pittsburgh. He is a speaker for Alcon Laboratories, Inc., but acknowledged no financial interest in the products or other companies mentioned herein. Dr. Condon may be reached at (412) 359-6298; garrycondon@gmail.com.
