Traditional glaucoma surgeries are effective at lowering
the intraocular pressure (IOP) but with a relatively high
incidence of complications, that can amount to 77%
(early and late) (1). In contrast, microincisional glaucoma
surgeries (MIGS) have a complication rate that is 10 to 20
fold lower(2)but were only in less advanced glaucoma until
recently(3-5). Although often advertised as new, procedures
that qualify as MIGS have been performed for more than
a century: for instance, Tailor performed angle surgery
in 1891 and Heine introduced suprachoroidal drainage
procedures in 1900(6). Many more MIGS types are now
available, including trabecular meshwork (TM) bypass stents
(iStent G1 and iStent G2 Inject, Glaukos, Laguna Hills, CA;
Hydrus, Ivantis, Irvine, CA, USA), TM ablation (Kahook
Dual Blade, New World Medical, Rancho Cucamonga,
CA, USA; Trabectome, Neomedix Inc, Tustin, CA, USA)
or disruption (Trab360, Sight Sciences, Menlo Park, CA,
USA) devices. There are subconjunctival (XEN, AqueSys,
Irvine, CA, USA) or suprachoroidal shunts (Gold Shunt,
SOLX, Waltham, MA, USA; CyPass, Transcend Medical,
Menlo Park, CA, USA; iStent G3 Supra, Glaukos, Laguna
Hills, CA, USA), and endocyclophotocoagulation (Endo
Optiks, Little Silver, NJ, USA). The CyPass is implanted via
an interno approach which is less invasive than ab externo as
necessary with the older SOLX Gold Shunt or the Aquashunt
(Opko Health, Miami, FL, USA) (7). Although both used
inert and biocompatible materials (gold and polypropylene),
a high rate of fibrosis can be seen even when combined
with antifibrotics(8-10). This is not surprising as the same
fibroblasts are present in the suprachoroidal space as in the
sub-tenon space that epibulbar devices face.
Although vessel scan been countered in the
suprachoroidal space, an earlier study with the very similar
Glaukos iStent Supra indicated that no serious complication
are normally seen (11). Despite being in direct contact with
the choroid, no progressive thinning has been reported as
seen with epibulbar devices. The newer CyPass microstent
is now FDA approved, and presents as a tubular polyimide
implant with a 310 μm internal diameter and many smaller
openings of 76 μm at the distal end. This material is a
synthetic resin in which the polymer units are linked by
imide groups, as used chiefly for heat-resistant films and
coatings but also applied to neuroelectrodes because it
allows conductivity.
The results from the Two-Year COMPASS Trial (12) have now become available (12) and confirm the safety and
efficiency of the CyPass. Vold et al. assessed this device for
mild-to-moderate primary open angle glaucoma patients
undergoing phacoemulsification. This study was well
designed, and the manuscript is well written. It provides
a convincing and in-depth assessment of methods and
results by detailing power calculations, statistics, and
group compositions. The authors used an image that we
published in 2013 (13) to highlight the device’s features
but mislabeled it as ocular coherence tomography (OCT)
while this transscleral imaging requires ultrasound biomicroscopy (UBM).
A total of 505 patients were enrolled and randomized
into phacoemulsification alone group (n=131) and compared
to a combined surgery group (CyPass microstent plus
phacoemulsification, n=374) at a ratio of 1:3. The baseline
IOPs and numbers of medication were the similar in both
groups (24.5±3.0 vs. 24.4±2.8 mmHg, 1.3±1.0 and 1.4±0.9,
P>0.05, respectively). At 24 months postoperatively, 21%
of IOP reduction in phacoemulsification alone group and
30% of IOP reduction in the combined surgery group
were achieved respectively (P<0.01). The 77% of patients
from the combined surgery group obtaining over 20% of
IOP reduction, compared with 60% in phacoemulsification
alone group (P=0.001), suggesting an additional IOP
lowering effect exists by CyPass microstent implantation.
A slightly lower number of glaucoma drops were needed
in the study group (0.2±0.6 vs. 0.6±0.8, P<0.001) at the
24 months. In total, 84.8% of combined surgery patients
were medication free compared to 59.1%. No visionthreatening
complication was encountered. BCVA loss ≥2
lines, visual field loss progression, iritis, corneal edema,
hyphema, stent obstruction, cyclodialysis cleft, postoperative
ocular hypertension, and hypotony were recorded, but most
of them were transient. About 5% of patients in the both
groups needed a secondary glaucoma surgery. All ab interno
MIGS procedures, including this one, are not affected by
conjunctival scar formation (5) and can be performed as
secondary procedures as long as the angle can be visualized,
a requirement that is not necessary with ECP or secondary
tubes or trabeculectomies. It is surprising that a cyclodialysis
forming procedure like the CyPass produces an IOP of around
16.5 mmHg, very similar to the other MIGS that are limited
by the episcleral venous pressure (2) which may not be low
enough for advanced glaucoma. Cleft forming procedures
that are device free (14) can, in theory, achieve much lower
pressures and are a major cause of hypotony unless the flow
is restricted by fibrosis or tissue juxtaposition.
As seen in several publications and consistent with this
paper, the Cypass has a favorable safety profile (12,15-18).
The incidence of stent obstruction was 2.1% (12) to
8.8% (15), mainly due to synechiae formation (16), too deep
insertion into the supraciliary space (16) and overgrowth
of iris cells (18). Transient hypotony was more common
[from 2.9% (12) to 15.8% (18)] than ocular hypertension
[3% (16) to 10.8% (17)]. Transient hyphema occurred
between 1.2% (16) and 6.2% (17). Repositioning and
explantation sometimes were necessary (16,18) due to the
dislocation of the implant. A few patients had endothelial contact with the stent (16,18) a potentially serious issue
which can lead to corneal decompensation.
In conclusion, this publication shows that the CyPass
holds promise as a new route to lowering IOP with relative
ease and safety. As with many new glaucoma surgeries,
surgeons have to take into consideration that the sample
size and follow-up is still relatively limited and no direct
comparison to other glaucoma surgeries exist (12,15-18). It
would be remarkable if the material used here, polyimide,
is so fundamentally different from prior used ones that it
allows a sustained, fibrosis free function.
