IOP reduction in OAG

Clinical data shows that when a single iStent is inserted in conjunction with cataract surgery, it lowers IOP by 33% on average, without significantly impacting the safety profile of cataract surgery alone.¹ That is no small accomplishment, especially as patient expectations following cataract surgery continue to raise the bar for surgeons. However, there are cases when mining of the conventional outflow pathway for aqueous does not provide sufficient lowering of intraocular pressure (IOP).

Clinical potential

The uveoscleral outflow stent was tested in 73 eyes with uncontrolled glaucoma with two medications, to gauge the efficacy of one stent and one medication (Travoprost). The group of all phakic eyes had a mean IOP of 20.4 ± 2.4 mmHg on two medications at the time they were admitted to the study, and a mean IOP of 24.8 ± 1.7 post-washout. The mean best-corrected visual acuity was 0.7 ± 0.3 (decimal notation; ~20/30) at baseline.

Following implantation of the device in all eyes without complications, 98% met the primary endpoint of ≥20% reduction of IOP, with a mean reduction of 47%. All eyes met the secondary endpoint of IOP ≤ 18 mmHg with the stent and one hypotensive medication (Travoprost). For the 32 eyes that were followed through 18 months, the mean IOP was 12.6 mmHg on one medication. Final study results will be published once all patients reach 24 months follow-up.

Peri- and postoperatively, the iStent supra demonstrated efficacy with a low risk safety profile. Two eyes experienced transient hypotony at 1 week, which resolved by the 1-month postoperative evaluation. One of these eyes also manifested a choroidal detachment, which resolved by the 3-month postoperative evaluation. Two subjects had progression of pre-existing cataracts. Otherwise, visual acuity remained unchanged. These data suggest that this third generation device is capable of significant IOP reduction, along with medication reduction, when implanted as a sole procedure in patients with primary open-angle glaucoma (POAG).

Conclusions

Studies have shown that filtration surgery is associated with a decrease in the size of Schlemm's canal,³ a finding that is not characteristic of OAG patients who are treated with medication. Thus, restoring physiologic outflow with a MIGS device that provides a superlative safety profile should be the first objective. If necessary, a prostaglandin can be added to one or two trabecular bypass devices to reach desired target pressures. When this is not sufficient, an iStent supra device may be implanted for additional benefit. The pipeline of low-risk, minimally invasive surgical treatment options for glaucoma will continue to grow in the near future.

References

1. T.W. Samuelson et al., Ophthalmology, 2011;118(3):459–467.

2. G. Auffarth, 'Results of ab interno suprachoroidal stent implantation and postoperative travoprost for treatment of open-angle glaucoma'. Presented at the annual meeting of the ASCRS, April 2013; San Francisco, California, USA.

3. D.H. Johnson and Y. Matsumoto, Arch. Ophthalmol., 2000;118:1251–1256.