Differences in Outflow Facility between Angiographically Identified High- versus Low-flow Regions of the Conventional Outflow Pathways in Porcine Eyes

Abstract

Purpose : To investigate differences in outflow facility between angiographically determined high- and low-flow segments of the conventional outflow pathway in porcine eyes.

Methods : Porcine anterior segments (n = 14) were mounted in a perfusion chamber and perfused using Dulbecco’s phosphate buffered solution with glucose. Fluorescein angiography was performed to determine high- and low-flow regions of the conventional outflow pathways. The trabecular meshwork (TM) was occluded using cyanoacrylate glue, except for residual 5 mm TM areas that were either high- or low-flow at baseline. This step designated these eyes as "residual high-flow” or “residual low-flow” eyes. Subsequently, outflow was quantitatively re-assessed and compared between “residual high-flow” and “residual low-flow” eyes followed by indocyanine green angiography.

Results : Fluorescein aqueous angiography demonstrated high-flow and low-flow regions. Before TM occlusion, baseline outflow facilities were 0.320 ± 0.08 and 0.328 ± 0.10 ml/min/mmHg (p=0.676) in eventual “residual high-flow” and “residual low-flow,” respectively. After partial trabecular meshwork occlusion, outflow facility decreased to 0.209 ± 0.07 µl/min/mmHg (- 32.66 ± 19.53 %) and 0.114 ± 0.08 µl/min/mmHg (- 66.57 ± 23.08 %) in residual high- and low-flow eyes (p=0.035), respectively. There was a significant difference in the resulting IOP increase (31.03 ± 8.51 mm Hg [residual low-flow] vs. 21.30 ± 6.57 mm Hg [residual high-flow]; p=0.034). Various aqueous humor outflow patterns were seen after occlusion using indocyanine green angiography.

Conclusions : Angiographically determined high- and low-flow regions in the conventional outflow pathways differ in their segmental outflow facility. Thus, there is an uneven distribution of local outflow facility across different parts of the TM. Future investigation into these regions across different parts of the TM could offer potential therapeutic targets regarding IOP regulation and lowering.

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