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72
EW RESIDENTS
November 2012
EyeWorld journal club
Review of “Using multiple trabecular
patients to treat open-angle glaucoma”
by Ambika Hoguet, M.D., Timothy Sullivan, M.D., Kevin Rosenberg, M.D., Peter Chang, M.D., and Paul A. Sidoti, M.D.,
program director, New York Eye and Ear Infirmary, New York
Paul A. Sidoti, M.D.
This month, I invited the New York Eye
and Ear Infirmary residents to review
this paper on micro-bypass stents,
which is very timely in light of the
recent FDA approval of the iStent.
—David F. Chang, M.D.,
EyeWorld chief medical editor
he iStent implant (Glaukos
Corp., Laguna Hills, Calif.)
is an ab interno trabecular
bypass device that was
recently FDA approved for
use in patients with open-angle
glaucoma who are undergoing
cataract surgery. The iStent is among
T
a small but growing number of minimally invasive surgical treatments
for glaucoma that are associated
with significantly reduced rates of
serious complications (such as infection, suprachoroidal hemorrhage,
choroidal effusion, and ocular
hypotony) relative to traditional
external drainage procedures such as
trabeculectomy and aqueous shunt
implantation. There is growing literature supporting the relative effectiveness of the iStent in increasing
the outflow facility of aqueous
humor from the eye. Several authors
have reported the effectiveness of
single stent implantation in lowering IOP for patients with mild to
moderate glaucoma.1-4
In “Using multiple trabecular
micro-bypass stents in cataract
patients to treat open-angle glaucoma,” published in the November
Using multiple trabecular microbypass stents in cataract patients
to treat open-angle glaucoma
Graham W. Belovay, M.D., Abdulla Naqi, M.D., Brian J. Chan, B.H.Sc.,
Mahmoud Rateb, M.D., Iqbal (Ike) K. Ahmed, M.D.
J Cataract Refract Surg (Nov) 2012; 38: 1911-1917
Purpose: To evaluate the efficacy of multiple trabecular micro-bypass
stents combined with cataract surgery in patients with open-angle
glaucoma (OAG) and cataract.
Setting: Private practice, Mississauga, Ontario, Canada.
Design: Comparative case series.
Methods: Eyes with OAG had implantation of 2 or 3 micro-bypass stents
with concurrent cataract surgery and follow-up through 1 year. Efficacy
measures were intraocular pressure (IOP) and topical ocular hypotensive
medication use. Safety assessment included complications and corrected
distance visual acuity (CDVA).
Results: The study comprised 53 eyes (47 patients); 28 had implantation
of 2 stents and 25 had implantation of 3 stents. The overall mean 1-year
post-operative IOP was 14.3 mm Hg, which was significantly lower than
pre-operative IOP overall and in each group (P<.001). The target IOP was
achieved in a significantly higher proportion of eyes at 1 year versus preoperatively (77% versus 43%; P<.001). Overall, 83% of eyes had a decrease
in topical ocular hypotensive medication at 1 year from pre-operatively,
with a 74% decrease in the mean number of medications (from 2.7 to 0.7)
at 1 year (P<.001). The 3-stent group was on significantly fewer
medications than the 2-stent group at 1 year (0.4 versus 1.0; P=.04).
Conclusions: Using multiple micro-bypass stents with concurrent cataract
surgery led to a mean post-operative IOP of less than 15 mm Hg and
allowed patients to achieve target pressure control with significantly fewer
medications through 1 year.
Financial disclosure: Dr. Ahmed is a consultant to Glaukos Corp. No
other author has a financial or proprietary interest in any material or
method mentioned.
issue of the Journal of Cataract &
Refractive Surgery, Belovay, et. al.
discuss the effects of using multiple
trabecular micro-bypass stents at the
time of cataract surgery to lower IOP
and reduce medication burden in
patients with coexisting glaucoma
and cataract. The purpose of this
study was to evaluate the safety and
effectiveness of multiple stent implantations and to determine
whether additional stents provided
any incremental benefit with respect
to IOP reduction and the need for
glaucoma medications. As glaucoma
remains a leading cause of blindness
worldwide, we applaud the authors
for attempting to further elucidate
the clinical effectiveness of this new
surgical alternative for lowering IOP
and potentially limiting or preventing disease progression in patients
with open-angle glaucoma.
The current study was designed
as an observational, open-label, nonrandomized, prospective, single-center study. A sample size of 53 eyes of
47 patients was included. As the
term observational indicates, there
was no control group or random assignment to treatment groups. Additionally, both the study patients and
investigators were aware of the treatment (i.e., the number of stents)
being administered. The inclusion
criteria for this study were visually
significant cataract “requiring
surgery” and IOP that was poorly
controlled on medications or that
required >3 medications for
adequate control. The severity of
glaucoma for each patient (mild,
moderate, or advanced) was determined using the clinical practice
guidelines of the Canadian Ophthalmological Society. Each patient
enrolled in the study underwent
implantation of two or three iStents
after phacoemulsification and IOL
implantation. Post-op, the IOP and
visual acuity were measured at 1 day,
1 week, and 1, 3, 6, and 12 months.
There was no statistically significant difference in any of the pre-op
characteristics evaluated for patients
in the two-stent versus the threestent group. Overall, the results of
the study pointed toward a favorable
result in patients undergoing
cataract extraction and multiple
iStent placements. The authors
reported a significant decrease in
mean post-op IOP at 1 year, com-
pared with the pre-op level for all
patients (p<0.001), with 70% of eyes
achieving an IOP of 15 mm Hg or
less and 77% reaching their target
IOP. This effect held up when
evaluating the two- and three-stent
groups separately. Although there
was a slightly greater mean reduction in IOP following surgery for
eyes in the three-stent (mean reduction 3.9 mm Hg) versus the twostent (mean reduction 3.5 mm Hg)
group, this difference did not reach
statistical significance (p=0.76). The
mean number of glaucoma medications required to control IOP at 1
year post-op was reduced by 74%
relative to the pre-op number for all
patients (p<0.001). Adjunctive glaucoma medications were decreased
from a pre-op average of 2.7 to an
average of 0.7 one year following
surgery with 83% of patients using
fewer medications. Patients with
three stents required significantly
fewer medications at 1 year (85%
mean reduction relative to pre-op
number) compared with those
receiving two stents (64% mean
reduction relative to pre-op number)
(p=0.04).
During the 1-year follow-up period of the study, few complications
were reported. The most common
was blockage of the stent lumen,
which was treated successfully using
a YAG or argon laser in six of the
eight eyes in which this occurred.
From the authors’ description, it
appears that the proximal opening
of the stent in the anterior chamber
became obstructed in these patients.
It is unclear how frequently distal
obstruction of a stent (not visible on
examination or amenable to laser
treatment) may have occurred.
Other complications included one
eye with hyphema and two eyes
with a presumed steroid-induced
IOP elevation. As the authors point
out, this is a relatively safe procedure for most patients. The visual
acuity outcome for patients in this
study is somewhat concerning. The
authors report that 15 (29%) of the
patients had a corrected distance visual acuity (CDVA) at 1 year following surgery of 20/50 or worse. Five
of these eyes demonstrated worsening CDVA relative to their pre-op
level. Unfortunately, no explanation
for either the reduction of CDVA or
failure of CDVA to improve at 1 year
November 2012
EW RESIDENTS
73
micro-bypass stents in cataract
New York Eye and Ear Infirmary ophthalmology residents (left to right) Ambika Hoguet, M.D., Kevin Rosenberg, M.D.,
Timothy Sullivan, M.D., and Peter Chang, M.D.
Source: Paul A. Sidoti, M.D.
following surgery is provided. The
authors imply in the discussion that
“advanced glaucoma” may have
been the cause, but no information
is provided to validate the extent to
which this is the case or to exclude
other factors.
There are some significant
limitations to this study that must
be considered in evaluating the
strength of the authors’ conclusions.
No specific exclusion criteria are
provided, and it is unclear if consecutive patients meeting the inclusion
criteria were offered enrollment or if
selected patients were excluded from
participation based on factors such
as the density of the cataract, the
degree of IOP elevation, or the
severity of glaucoma damage.
Selective enrollment of patients,
even if unintentional, may have
had an effect on the study results.
Although the authors claim that
77% of eyes achieved their target
IOP at 1 year post-op, they also indicate that, even before surgery, 43%
of the patients already had achieved
their target IOP with a combination
of medications and/or laser trabeculoplasty. Although the authors
stratified the data according to the
number of stents (two versus three)
placed in each patient, we feel it
would be helpful to also see the outcome data stratified by the severity
of glaucoma. The lack of a standardized protocol for discontinuing or
restarting medications following surgery may also have confounded the
results. It is unclear if the mean
number of post-op glaucoma medications would have been decreased
in either or both treatment groups
or if the difference in medication
use at 1 year would have been
affected if such a standardized
protocol had been employed. It is
possible, for example, that there was
a greater tendency on the part of the
investigators to discontinue medications in eyes that had received three
as opposed to two stents or to maintain pre-op medications in patients
with more advanced glaucoma.
As the authors concede, the
observational nature of this study
and lack of random assignment to
treatment groups make it difficult to
ascertain how much of the pressurelowering effect and reduction in
medication burden for these patients
was due to the incremental contribution of each stent. Although the
authors state that patients requiring
“greater IOP control” had three
stents implanted instead of two, no
specific criteria for determining the
desired post-op target IOP or the
desired degree of IOP reduction (as a
percentage of the pre-op IOP or an
absolute value) were provided. Random assignment of patients to the
two-stent or three-stent treatment
groups would allow more accurate
assessment of any additional IOP
lowering, greater or more prolonged
stability of IOP reduction, and additional reduction in the number of
post-op glaucoma medications
achieved by the use of an additional
stent. Additionally, the inclusion of
both eyes of six patients may have
introduced further bias.
Despite its limitations, this
study provides valuable data on the
effectiveness of phacoemulsification
combined with iStent placement in
patients with cataract and coexisting
glaucoma. The authors have demonstrated that the implantation of two
or three trabecular micro-bypass
stents combined with cataract
surgery is both safe and effective,
resulting in clinically significant IOP
and medication reduction and the
potential to achieve target IOP levels
appropriate for all degrees of
glaucoma severity. Moreover, the
relatively greater reduction in the
number of post-op glaucoma medications in the cohort of patients
receiving three stents as opposed to
that receiving two stents indicates
that the effect of multiple stents
may be additive. The excellent risk
profile of this procedure as well as its
minimal invasiveness (performed
through a small corneal incision
without any disturbance to the conjunctiva) minimizes its potential impact on future surgical management
options for glaucoma and may make
iStent placement a reasonable option to enhance IOP control or reduce medication burden in patients
with glaucoma who are undergoing
cataract surgery. Further work is
warranted to clarify the relative
effect of stent placement and con-
current phacoemulsification to the
overall pressure-lowering effect of
the combined surgery.
It is important to bear in mind
that glaucoma is a chronic disease
that is dynamic in many respects.
Longer follow-up of patients in a
study such as this is warranted to
assess continued stability of IOP
control, ascertain whether a differential IOP-lowering effect between
the two- and three-stent groups
develops over time, and determine
whether the need for fewer post-op
glaucoma medications in the threestent group is maintained. Continued monitoring of the study patients
for the development of long-term
complications is also essential.
Further studies comparing the iStent
to different glaucoma treatment
options, assessing its safety and
effectiveness over longer follow-up
periods, and using better guidelines
for determining number of stents
implanted in each patient would be
valuable in understanding the
relative merits of trabecular microbypass stent surgery and its role in
glaucoma management. It will also
be important to assess impact of the
iStent implant in halting disease
progression based on structural
assessment of the optic disc and
functional parameters such as visual
field testing. EW
References
1. Craven ER, Katz LJ, Wells JM et al. Cataract
surgery with trabecular micro-bypass stent
implantation in patients with mild-to-moderate open-angle glaucoma and cataract: two
year follow-up. J Cataract Refract Surg 2012;
38: 1339-45.
2. Fea AM. Phacoemulsification vs. phacoemulsification with micro-bypass stent implantation in primary open-angle glaucoma:
randomized double-masked clinical trial. J
Cataract Refract Surg 2010; 36: 407-412.
3. Samuelson TW, Katz LJ, Wells JM et al.
Randomized evaluation of the trabecular
micro-bypass stent with phacoemulsification
in patients with glaucoma and cataract.
Ophthalmology 2011; 118:459-67.
4. Speigel D, Wetzel W, Neuhann T et al.
Coexistent primary open-angle glaucoma and
cataract: interim analysis of trabecular microbypass stent and concurrent cataract surgery.
Eur J Ophthalmol 2009; 19:393-9.
Contact information
Sidoti: [email protected]