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Page 6 of 14 Komzak et al. Mini-invasive Surg 2021;5:13 I http://dx.doi.org/10.20517/2574-1225.2020.103

iStent and iStent inject: Effectiveness
[5]
Hooshmand et al. found that iStent and iStent inject (both combined with phacoemulsification) had
comparable effectiveness in practice, with their study of 145 eyes with primary OAG showing 56.0% of
the iStent and 51.3% of the iStent inject eyes achieved an IOP value of ≤ 18 mmHg and were medication
[10]
free at 12 months. In a randomised prospective trial conducted by Samuelson et al. , iStent inject with
phacoemulsification was compared with phacoemulsification alone in terms of safety and efficacy. The
proportion of eyes that had achieved an IOP reduction of ≥ 20% from baseline at 24-month follow-up was
75.8% in treatment eyes compared with 61.9% of eyes in the control group. 84% of treatment eyes compared
[10]
with 67% of control eyes were medication free at the 23-month follow-up .
[9]
It has also been demonstrated in an RCT by Katz et al. that increasing the number of iStent devices
implanted as a standalone procedure leads to an increased treatment effect. Whilst all patients in this trial
were taking between one to three topical medications pre-implantation, all were taken off post-operatively,
and in the 1-iStent group 18/38 participants required the addition of a topical medication by 42 months,
[9]
compared with 4/41 in the 2-iStent group and 3/40 in the 3-iStent group .

iStent trabecular microbypass devices have also demonstrated efficacy in secondary OAG. In one 24-eye
study of iStent in combination with phacoemulsification in pigmentary glaucoma there was a reduction
in IOP from 19.50 ± 6.7 mmHg at baseline to 14.68 ± 3.0 mmHg (P < 0.01) at 36 months in addition to a
[6]
reduction in medications from 0.75 ± 1.0 topical medications to 0.59 ± 0.6 (P > 0.05) . Pseudoexfoliation
[7]
glaucoma was also investigated by Ferguson et al. , with iStent implantation in combination with
phacoemulsification in 115 eyes leading to a statistically significant reduction in mean IOP and topical
medication usage at 2 years. No studies were identified that solely investigated iStent or iStent inject in
steroid induced glaucoma.

iStent and iStent inject: Safety profile
[10]
Samuelson et al. reported the overall adverse events to be less frequent in the intervention group
who received iStent and phacoemulsification (54.1%) vs. the control group (who only received cataract
extraction) (62.2%), and the majority of these were minor complications, the most common being ocular
surface disease, stent obstruction, intraocular inflammation, secondary surgical inflammation and ocular
allergies. Of those who had stent obstruction (n = 24), 3 had a laser revision to clear the blockage and these
[10]
were all successful .
Hydrus: Mechanism of action and effectiveness
The Hydrus microstent (Ivantis inc, Irvine, CA, USA) is an 8-mm intracanalicular scaffold that dilates an
entire 90˚ quadrant of Schlemm’s canal to increase aqueous humor flow through the trabecular meshwork
(displayed in Figures 2 and 3). The Hydrus implant is introduced in a fashion similar to other trabecular
microbypass stents, through a clear corneal incision with phacoemulsification or as a single procedure, and
with the application of a topical corticosteroid and antibiotic solution during the post-operative period.
The indication for Hydrus is mild to moderate glaucoma with the aim of reducing dependence on topical
[26]
medication and to control IOP within a suitable target .

The efficacy of Hydrus in combination with phacoemulsification compared to phacoemulsification alone
was investigated in the recent HORIZON study by Samuelson et al. In this 369-eye study, an unmedicated
IOP reduction of > 20% was achieved in 77.3% of Hydrus eyes compared with 57.8% of control eyes at 24
months. There was a mean reduction of 7.6 ± 4.1 mmHg in the Hydrus group and 5.3 ± 3.9 mmHg in the
phacoemulsification alone group. Mean medication burden was reduced from 1.7 ± 0.9 pre-operatively
(baseline value in both intervention and control was equivalent) to 0.3 ± 0.8 in the Hydrus group and to 0.7
[4]
± 0.9 in the phacoemulsification alone group .