Outflow Facility Effects of 3 Schlemm's Canal Microinvasive Glaucoma Surgery Devices

Abstract

Purpose: To study the effect of 3 Schlemm's canal (SC) microinvasive glaucoma surgery (MIGS) devices on outflow facility.

Design: Paired comparisons, randomized design, baseline-controlled study.

Participants: Thirty-six pairs of dissected anterior segments from donated human eye bank eyes without glaucoma were studied. A baseline measurement was collected from each eye to serve as its control.

Methods: Using a constant pressure perfusion method, outflow facility was measured in paired eyes from human donors. Measurements were made at perfusion pressures of 10 mmHg, 20 mmHg, 30 mmHg, and 40 mmHg. Outflow facility was measured before (baseline control) and after the implantation of an SC glaucoma drainage device or sham procedure. Three sets of experiments were carried out comparing 1 and 2 iStent Trabecular Micro-Bypass Stents and 2 iStent Inject implants with the Hydrus Microstent.

Main outcome measures: Change in outflow facility from baseline or contralateral eye.

Results: After Hydrus placement, the outflow facility increased from 0.23±0.03 μl/minute per millimeter of mercury at baseline to 0.38±0.03 μl/minute per millimeter of mercury (P < 0.001). The percent increase in outflow facility was 79±21% for the Hydrus and 11±16% for the 2 iStent Inject devices, a difference that was significant (P = 0.018). Outflow facility with 1 iStent (0.38±0.07 μl/minute per millimeter of mercury) was greater than baseline (0.28±0.03 μl/minute per millimeter of mercury; P = 0.031). The 1 iStent showed a greater increase in outflow facility from baseline (0.10±0.04 μl/minute per millimeter of mercury) compared with the sham procedure (-0.08±0.05 μl/minute per millimeter of mercury; P = 0.042). No other significant differences were found.

Conclusions: The longer the MIGS device, and thus the more SC that it dilates, the greater the outflow facility.