Page 126 - Read Online

Komzak et al. Mini-invasive Surg 2021;5:13 I http://dx.doi.org/10.20517/2574-1225.2020.103 Page 11 of 14

Xen: Mechanism of action and effectiveness
The XEN gel implant (Allergan inc, Irvine, CA, USA) was a form of MIGS targeting aqueous outflow to
the subconjunctival space; however, in November 2019, Allergan Australia Pty Ltd. announced that there
would be a voluntary global recall of all un-implanted XEN units due to a portion of them failing quality
[27]
control. They did not recommend the explantation of implants that had already been placed .

The XEN gel stent was implanted into the trabecular meshwork with a needle through an ab-interno
approach, which was then advanced to puncture the sclera entirely and pass the flexible stent into the sub-
conjunctival space. This then creates a channel for aqueous humour outflow and creates an internal bleb
to reduce IOP. XEN was indicated for moderate to advanced glaucoma, as it was a bleb-based procedure
[22]
with the associated risks/complications associated with this. Karimi et al. investigated the efficacy of
XEN alone or in combination with phacoemulsification with a 259 eye consecutive case series. The results
showed that mean IOP (of both groups combined) was reduced from 19.3 ± 6.0 mmHg at baseline to 13.5 ±
3.3 mmHg at 18-month follow-up, and medications were reduced from 2.6 ± 1.1 to 1.1 ± 1.3 at 18 months.
It was also interesting to note that simultaneous cataract extraction or solo stent implantation did not
significantly impact outcomes, as these groups had an IOL of 13.8 ± 2.6 mmHg and 14.3 ± 4.7 mmHg at
[22]
12-month follow-up, respectively (P = 0.5367) .
As a form of bleb forming procedure, it is also important to compare the XEN gel stent with trabeculectomy,
which is still the predominant incisional procedure for glaucoma. Wagner et al. compared the 2 as standalone
[23]
procedures performed in a 171-eye study, which demonstrated that complete surgical success at 12 months
post-operative follow-up was higher in the trabeculectomy group at 65.5% (95%CI: 55.6%-75.9%) compared
with the XEN gel stent group at 58.5% (95%CI: 47.6%-69.4%). There was however no significant difference
between both groups’ surgical outcomes (P = 0.16). In addition, an IOP reduction at 12-month follow-up
of 7.2 ± 8.2 mmHg in the XEN group and 10.5 ± 9.2 mmHg in the trabeculectomy group were observed
from baseline values of 19.0 mmHg (95%CI: 16.8-25.0 mmHg) and 21.0 mmHg (95%CI: 17.0-27.0 mmHg),
respectively (P = 0.003). Medication reduction was also reduced to 0.3 ± 0.5 and 0.2 ± 0.4 in the XEN and
trabeculectomy cohorts, respectively from baseline values of 2.0 (95%CI: 1.0-3.0) and 3.0 (95 CI: 2.0-4.0),
[23]
respectively .
The XEN gel stent was also shown to have comparable efficacy in other secondary forms of open angle
[24]
glaucoma, including pseudo exfoliation glaucoma as demonstrated by Gillmann et al. , where 110 eyes
with either pseudoexfoliative OAG or POAG underwent either XEN as a standalone or with cataract surgery
(with data combined). In this study the mean medicated IOP was 14.2 ± 3.8 mmHg (a 28.3% reduction) in
the pseudoexfoliative group compared with 14.5 ± 3.6 mmHg (a 26.8% reduction) in the POAG group after
2 years, a reduction from 19.8 ± 8.2 mmHg and 19.8 ± 5.8 mmHg respectively. Medication reduction was also
comparable, with a drop from 2.0 ± 1.3 to 0.4 ± 0.7 in pseudoexfoliation glaucoma and from 1.9 ± 1.6 to 0.6 ±
0.9 in POAG. Success rates were not different to a statistically significant degree, and the rate of adverse effects
[24]
and rates of needling were similar in both groups (42.8% POAG vs. 43.2% pseudoexfoliative) . There were no
studies showing evidence of the efficacy of the XEN implant in pigmentary or steroid induced glaucoma.

Xen: Safety profile
Important to note is that 40.9% of cases required post-operative management including bleb needling
or the administration of an antimetabolite injection, and adverse events included IOP spikes of ≥ 30
mmHg (12.7%), follow-up glaucoma filtration surgery (9.3%), exposure of the implant (2.3%) aswell as
some cases of persistent hypotonous maculopathy, persistent choroidal effusions, a cyclodialysis cleft and
[22]
endophalmitis following bleb resuturing . This is partially to be expected with a bleb forming operation
and reflects the safety profile of this class of procedure.

Preserflo microshunt: Mechanism of action, effectiveness, and safety profile