1. Outflow facility in cadaveric eyes increased from a baseline of 0.28 ± 0.10 µL/min/mmHg to 0.44 ± 0.13 µL/min/mmHg after implantation of the Hydrus microstent (p=0.001).
2. Compared to cadaveric eyes implanted with iStents, eyes implanted with the Hydrus scaffold had a significantly greater increase in outflow facility from baseline (increase of 0.08 vs. 0.16 µL/min/mmHg respectively; p=0.03).
Evidence Rating Level: 2 (Good)
Study Rundown: Glaucoma is the most common cause of irreversible blindness globally. Elevated intraocular pressure (IOP) is the only modifiable risk factor in developing glaucoma. Management of glaucoma includes medical and surgical therapy, with surgical techniques aimed at reducing IOP by increasing the outflow of aqueous humor. Multiple surgical stenting or scaffolding devices have been developed to augment outflow. The iStent is an FDA-approved bypass stenting device, while the Hydrus microstent scaffold is a device that is positioned within Schlemm’s canal and is currently in clinical development. In this study, the authors demonstrated that the Hydrus stent significantly improves outflow through cadaveric human eyes, and substantially more than a combination of two iStents (74% vs. 34%; p=0.03). Outflow resistance was decreased significantly with the Hydrus. Limitations of this study include the high standard deviations due to the relatively small sample size. Nonetheless, these data demonstrate that the Hydrus may be a valuable addition to the glaucoma surgical armamentarium.
In-Depth [basic science study]: In this study, researchers obtained twelve pairs of eyes from human donors. Eyes were perfused at five different pressures using a saline solution, after which two different devices were implanted in the eyes. In one of the two paired eyes, the Hydrus scaffold was inserted. In the other eye, two iStents were placed within a distance equivalent to the length of the Hydrus scaffold. Outflow facility, which represents the inverse of outflow resistance, was measured in these eyes after the intervention. Outflow facility in cadaveric eyes increased from a baseline of 0.28 ± 0.10 µL/min/mmHg to 0.44 ± 0.13 µL/min/mmHg after implantation of the Hydrus microstent (p=0.001). Compared to cadaveric eyes implanted with iStents, eyes implanted with the Hydrus scaffold had a significantly greater increase in outflow facility from baseline (0.08 vs. 0.16 µL/min/mmHg respectively; p=0.03). Calculated outflow resistance was significantly lower in the Hydrus group. These data appear to suggest that both devices are effective in augmenting outflow of aqueous humor, but that the Hydrus scaffold may actually outperform the iStent device.
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