Improvement in outflow facility by two novel microinvasive glaucoma surgery implants

Abstract

Purpose: To determine improvement in outflow facility (C) in human anterior segments implanted with a novel Schlemm's canal scaffold or two trabecular micro-bypasses.

Methods: Human anterior segments were isolated from 12 pairs of eyes from donors with no history of ocular disease and then perfused at 50, 40, 30, 20, and 10 mm Hg pressures for 10 minutes each. Baseline C was calculated from perfusion pressures and flow rates. The scaffold was implanted into Schlemm's canal of one anterior segment, and two micro-bypasses were implanted three clock-hours apart in the contralateral anterior segment. Outflow facility and resistance were compared at various standardized perfusion pressures and between each device.

Results: Compared to baseline, C increased by 0.16 ± 0.12 μL/min/mm Hg (74%) with the scaffold, and 0.08 ± 0.12 μL/min/mm Hg (34%) with two micro-bypasses. The scaffold increased C at perfusion pressures of 50, 40, 30, and 20 mm Hg (P < 0.005). Two micro-bypasses increased C at a perfusion pressure of 40 mm Hg (P < 0.05).

Conclusions: Both implants effectively increased C in human eyes ex vivo. The scaffold increased C by a greater percentage (73% vs. 34%) and at a greater range of perfusion pressures (20 to 50 mm Hg vs. 40 mm Hg) than the two micro-bypasses, suggesting that the 8-mm dilation of Schlemm's canal by the scaffold may have additional benefits in lowering the outflow resistance. The Hydrus Microstent scaffold may be an effective therapy for increasing outflow facility and thus reducing the IOP in patients with glaucoma.

Keywords: Schlemm's canal; drainage device; glaucoma anterior segment; outflow facility.

Figure 1

(A) Hydrus Microstent is 8 mm long with an open SC scaffold coupled with a trabecular meshwork bypassing inlet. (B) iStent micro-bypass has a snorkel with a 120-μm lumen and a 1-mm rail fitting into SC.

Figure 2

Representative photos of implants in the inferior nasal quadrant of anterior segments. Left column: Anterior segment (OS) with implanted scaffold. Arrows indicate flanks of scaffold. Right column: Anterior segment (OD) receiving two micro-bypasses. Arrows indicate a single stent. S, superior; N, nasal.

Figure 3

Calculated outflow facilities (C) for anterior segments with implanted scaffold or two micro-bypasses. Bars represent SEM. *P < 0.05 for scaffold versus baseline 1. †P < 0.05 for two micro-bypasses versus baseline 2. Baseline measurements from contralateral eyes were not significantly different (NS).

Figure 4

Changes in outflow facility (top graph) and resistance (bottom graph) from baseline by the scaffold or two micro-bypasses. Data are represented as mean ± SEM. *P < 0.05 change by scaffold versus change by micro-bypasses.

Figure 5

Combined baseline outflow facilities of both Hydrus and iStents receiving eyes (n = 24) at five perfusion pressures. Outflow facility at a perfusion pressure of 40 mm Hg was less than at 10, 20, and 30 mm Hg. *P < 0.05 compared with outflow facility at 40 mm Hg.

Figure 6

(A) Histological section of the scaffold window region in situ showing significant TM stretch and SC dilation. (B) Histological section of the micro-bypass rail in situ showing placement inside SC.