Greater Outflow Facility Increase After Targeted Trabecular Bypass in Angiographically Determined Low-Flow Regions Compared to High-Flow Regions

Abstract

Purpose : To investigate the impact of trabecular bypass surgery targeted to angiographically-determined high- versus low-aqueous humor outflow areas on outflow facility (C) ex vivo.

Methods : From porcine (n= 14) and human (n=13) post-mortem eyes, anterior segments were dissected, mounted onto a perfusion chamber, and perfused using Dulbecco’s phosphate buffered solution containing glucose at a constant-flow rate to achieve a stable baseline facility (C). Fluorescein was perfused into the anterior chamber and used to identify high- and low-flow regions of the conventional outflow pathways. A 5 mm needle goniotomy was performed in either baseline high- or low-flow areas. Subsequently, C was quantitatively re-assessed and compared between “high-flow” and “low-flow” surgery eyes.

Results : : In all anterior segments, high- and low-flow regions could be identified. Performing a 5 mm goniotomy increased C to a variable extent depending on their baseline. In the porcine high-flow group (n=8), C increased from 0.31 ± 0.09 to 0.39 ± 0.09 µL/mmHg/min (P = 0.12). In the porcine low-flow group (n=6), C increased from 0.29 ± 0.03 to 0.56 ± 0.10 µL/mmHg/min (P< 0.001). In the human high-flow group (n=6), C increased from 0.38 ± 0.20 to 0.41 ± 0.20 µL/mmHg/min (P = 0.02). In the human low-flow group (n=7), C increased from 0.25 ± 0.11 to 0.32 ± 0.11 µL/mmHg/min (P< 0.001). There was statistically significant greater C increase comparing low- to high-flow groups in both porcine (0.07 ± 0.09 vs 0.27 ± 0.13, P = 0.007 µL/mmHg/min, high- vs. low-flow) and human (0.03 ± 0.03 vs 0.07 ± 0.02, P = 0.03 µL/mmHg/min, high- vs. low-flow) eyes. In porcine eyes, there was a 27.83 ± 32.78% and 95.96 ± 56.65% (P = 0.02) increase in C for goniotomies in high- and low-flow regions, respectively. In human eyes, there was a 10.01 ± 13.63 % and 36.31 ± 21.71% (P = 0.03) increase in C for goniotomies in high- and low-flow regions (P = 0.02), respectively.

Conclusions : Targeting trabecular meshwork bypass surgery to low-flow areas of the trabecular meshwork yields greater outflow facility (C) increase compared to surgery in high-flow areas. In-vivo studies are needed to confirm this finding and translate it to improved efficacy of common MIGS procedures.

This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.