Schlemm’s Canal Outflow Resistance System (SCORS) visualized by Clarification and Immunohistochemistry (IHC)

Abstract

Purpose : Schlemm’s canal (SC) inner wall forms funnel-shaped regions that enter SC, narrow to form a tubular conduit with an endothelial-lined lumen and cross SC lumen to attach to the external wall in humans and NH primates. These SC inner wall valve-like (SIV) conduits attach to mobile leaflets forming a second SC outer wall valve-like arrangement (SOV) at collector channels (CC). The TM adheres to SOV-hinged flaps through SIV. Real-time OCT imaging demonstrates that the linkage permits pressure-induced TM motion to modulate CC entrance size. The purpose of our study is 1) To describe a novel combination of techniques permitting IHC to image a distal resistance system. 2) To further characterize the walls, lumen, and connections of the SIV.

Methods : Anterior segments of 16 M. Nemestrina primates underwent IHC labeling; 14 perfused with fluorescent microspheres (MS). Limbal tissues divided into quadrants, viscoelastic introduced into SC, and tissues fixed. Radial segments were cut, tissues clarified, confocal microscopy performed, imageJ 3D projections encompassing the TM, SC, and distal pathways obtained.

Results : 3D relationships between SIV, SOV, and CC were obtained with IHC confocal imaging. Imaging demonstrated CD 31, Collagen Type 1 & 4 in the walls surrounding the SIV lumen and distal pathways. In four eyes, 231 segments were examined, and 293 SIV were identified; 9.2% of the SIV contained microspheres.

Conclusions : Increased imaging depth with clarification and IHC permits the identification of SIV linkage between the TM and SOV. The SIV walls are continuous with SC inner wall endothelium; CD 31 vascular endothelial labeling is identical. Perfused MS demonstrated TM and lumen continuity. The attachments of the SIV to hinged flaps at SC external wall create the SOV. The relationships thus provide a mechanism to control CC entrance dimensions and regulation of distal resistance. The SIV-SOV relationships may provide a SC outflow resistance system.

This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.

 

Fluorescent microspheres (MS) enter and exit SC valve-like structures. Z-stack image depth following IHC with (A) Merged CD 31 (red), DAPI (blue), and 500 µm MS (green) channels. Two SIV attach to SC external wall. Complex distal attachment create a SOV. (B-D) The same SOV structure rotated around the Y-axis. (E-F) Merged IHC channels add the Nomarski view to better show the structure of the SIV and attachments to SC distal wall.