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MIGS aimed at creating an outflow channel to the supraciliary space
Mechanism of action, effectiveness, and safety profile.

CyPass: Mechanism of action and efficacy
CyPass (Transcend Medical Inc, Menlo Park, CA, USA) was a tubular stent which aimed to reduce IOP
by shunting fluid through a passage into the supraciliary space. It was performed through a clear corneal
incision, and the stent is placed inferior to the trabecular meshwork and advanced into the suprachoroidal
space. CyPass had proven efficacy in the COMPASS trial which compared CyPass combined with
phacoemulsification to phacoemulsification alone. It was shown that at 2 years, patients who had received
the CyPass microstent had a mean reduction in IOP of 7.4 ± 4.4 mmHg (30%) compared to 5.4 ± 3.9 mmHg
(21%) in the control group (P < 0.001 for CyPass microstent vs. control). A reduction from baseline values
of 17.0 ± 3.4 mmHg and 19.3 ± 3.3 mmHg, respectively. This efficacy was also shown in the reduction in
medications, as medications at 2 years had dropped from 1.4 ± 0.9 to 0.2 ± 0.6 in the CyPass group and
from 1.3 ± 1.0 to 0.6 ± 0.8 in the control group. At 2 years 85% of CyPass recipients had maintained their
[17]
IOP with no medications, compared to 59% in the phacoemulsification alone cohort .

[19]
CyPass has also been compared with iStent in a head-to-head meta-analysis by Fard et al. , and in that
study, they showed that CyPass alone (without phacoemulsification) was a more effective intervention for
reducing IOP than either 1 or ≥ 2 iStents with or without phacoemulsification, but both techniques were
comparable in terms of medication reduction.

CyPass: Safety concerns
The COMPASS XT study was an extension of the original 24-month study for an additional 36 months to
assess the safety of the stent. This study showed comparable safety between the study and control groups,
and while there were 2 sight threatening complications in the CyPass group compared with only one in
the control group, these were deemed to be unrelated to the stent. Despite this, evidence was found for
increased corneal endothelial cell loss compared with the group that underwent phacoemulsification alone,
and due to this it was announced in August 2018 that it would be voluntarily removed from the market by
[18]
Alcon due to the potential risks, with the potential for reintroduction in the future .
iStent Supra: Mechanism of action, effectiveness, and safety profile
iStent Supra (Glaukos Inc, Laguna Hills, CA, USA) is currently an experimental microbypass stent
[20]
which also harnesses the uveoscleral pathway similarly to CyPass. Myers et al. evaluated iStent Supra
in combination with 2 iStents and post-operative Travoprost for the treatment of refractory open angle
glaucoma following trabeculectomy and maximal medical therapy. The pre-operative mean medicated IOP
was 22.0 ± 3.1 mmHg, with 1.2 ± 0.4 medications on average. The post-operative mean medicated IOP
at 48 months was ≤ 13.7 mmHg (12.9 ± 0.9 mmHg at month 48) and unmedicated mean IOP was 18.4 ±
1.4 mmHg at month 49 (post-washout). The safety profile of the suprachoroidal stent was favourable, and
[20]
throughout the 48-month follow-up no patients required additional glaucoma surgery .
Assessing the efficacy of iStent supra in this form of study alone is challenging, as there are confounding
variables in the form of the 2 iStent devices, and the effects of the topical Travoprost. Further studies to
determine the efficacy of iStent supra would be beneficial, preferably in the form of randomised controlled
studies, and in comparison, with other methods or in combination with phacoemulsification.

MIGS targeted at the subconjunctival space
Mechanism of action, effectiveness, and safety profile.