Second-generation bypass stent shows promise for lowering IOP

This prospective laboratory study in the June issue of the American Journal of Ophthalmology found that the iStent inject (Glaukos Corporation, Laguna Hills, Calif.), a second-generation bypass stent, increased outflow facility and reduced pressure in cultured human anterior segments. The study's authors conclude that, like its predecessor the iStent, the iStent inject shows promise for lowering IOP via trabecular meshwork (TM) bypass.

The iStent inject system was developed to enable implantation of multiple stents to access more of the Schlemm canal (SC) and thus provide further IOP lowering in primary open-angle glaucoma patients. It is smaller than its predecessor and has a different design, with an injector preloaded with two stents and designed to improve ease of implantation. Multiple stents can be inserted while entering the eye only once.

The study was conducted using anterior segments from seven human donor eyes. One or two iStent inject stents were inserted into the TM within the nasal and/or superior quadrants. Afterward, anterior segments were returned to culture and perfused for an additional 24 hours.

Insertion of one iStent inject into the nasal or superior quadrant of the TM increased outflow facility from 0.16 ± 0.05 µL/min/mmHg to 0.38 ± 0.23 µL/min/mmHg (P < 0.03, n = 7), with concurrent pressure reduction from 16.7 ± 5.4 mmHg to 8.6 ± 4.4 mmHg. The addition of a second stent approximately 90 degrees superior to the first one further increased outflow facility to 0.78 ± 0.66 µL/min/mmHg (n = 2) and reduced pressure by another 5 mmHg.

Scanning electron microscopy showed the iStent inject flange compressed against the uveal region of the TM. Dilation of SC was noted around the iStent inject head and SC cell disruption was observed at the iStent inject insertion site. 3D micro-computed tomography confirmed iStent inject placement.

The authors note that the underlying principle of both the iStent and iStent inject remains the same: that bypassing the TM will improve fluid flow from the anterior chamber into SC. Similar to its predecessor, the iStent inject can be implanted via a corneal paracentesis. The authors say both generations of the iStent show increased outflow facility after placement of two stents, most likely by accessing additional portions of the SC and collector channels such that overall outflow resistance is reduced.