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Page 8 of 14 Komzak et al. Mini-invasive Surg 2021;5:13 I http://dx.doi.org/10.20517/2574-1225.2020.103

Figure 3. Hydrus microstent (Ivantis inc, Irvine, CA, USA) viewed gonioscopically in position in the canal of Schlemm. The device is
partially obscured by the overlying trabecular meshwork. Image copyright of Ivantis, Inc.

without the requirement for suturing. This acts to reduce IOP by dilating the canal of Schlemm and
downstream collector channels to improve aqueous outflow. The indication for ABiC in mild to moderate
glaucoma is either as a solo procedure or in combination with other forms of trabecular microbypass
devices to facilitate further dilation of the collecting channels, and greater outflow than would be achieved
with these devices alone, a similar principle to other non-implantation techniques specifically targeting
improved outflow through Schlemm’s canal.

ABiC has been evaluated as both a sole procedure in phakic eyes and in combination with cataract surgery
[11]
by Davids et al. In one study of 36 eyes (20 pseudophakic and 16 phakic) a reduction in mean IOP was
seen from 19.8 ± 4.1 mmHg pre-operatively to 13.8 ± 3 mmHg 12 months post-operatively across the 2
[11]
groups . There was, however, no statistically significant reduction in the number of medications during
this period, which stabilised at 2.1 ± 1.6 (P = 1.0). This would be an important point to include when
[11]
counselling patients about ABiC as a sole procedure .
[12]
ABiC also has the potential to be used as a combination therapy with other forms of MIGS. Heersink et al.
explored this concept in their 186-eye retrospective study comparing iStent and cataract surgery with
iStent, ABiC and cataract surgery. The results showed a clear favourability for the IOP lowering effects
of iStent with AbiC and phacoemulsification, as this group achieved a mean IOP reduction of 2.9 ±
3.6 mmHg compared with 1.7 ± 3.1 mmHg in the iStent and phacoemulsification groups alone. The
percentage of patients achieving treatment success (a final IOP of ≤ 18 mmHg and a mean reduction in
IOP of > 20%) was 46% in the combined group compared with 35% in the trabecular microbypass and
cataract surgery alone group. In terms of medication, 56% of patients in the combined group were off all
[12]
medications compared with 48% in the control group, a mean reduction of 0.9 and 0.7, respectively .

It is likely that ABiC would be an effective procedure to combine with existing trabecular microbypass
methods. As a sole procedure it is also effective at lowering IOP; however, it has showed limited efficacy in