Abstract
Purpose :
Definitive microvascular casting (MVC) evidence demonstrates collector channels exit SC, then immediately enter circumferential vascular channels (CVC) parallel to SC. Distal radial channels, noncontiguous with CC, lead from CVC to episcleral veins. OCT shows mobile pressure-dependent septa close the CVC, providing valve-like distal control system. Here, we characterize relationships quantitatively using SEM. MIGS benefits from knowledge of distal aqueous outlfow.
Methods :
Viscoelastic dilated 360 degrees of SC of 74 y/o C/M eye that was then fixed, divided into quadrants, meridional sections bisected along the SC circumferential axis. Counting structures of the corneal portion prevented double counting. SEM was done by standard procedures. ImageJ to measure & analyze images.
Results :
40 total SEM segment preparations: 9, 9, 11, 11 for IT, IN, ST, & SN quadrants, respectively. SC data: total length measured, 30,116 μm; mean SC segment length, 752±150 μm (range (R) 392-1069 μm); mean SC height at cut front edge perpendicular to the long axis, 69.5±23.6 μm (R 34.3-134.5); mean SC area 51,687±21,760 μm2. CC data: n=10. Mean height perpendicular to SC, 13.9±6.6 μm (R 6.0-28.4); length parallel to SC 44.3±24.9 μm (R 17.8-88.9); mean area 570.8±494.9 um2. CVC Data: Distance from SC, 100.2±50.9 μm (R 6.4-221.8); mean CVC height, 21.9±11.5 μm (R 8.3-64.4); mean length, 150.6±113.8 μm (R 35.4-691); Mean aspect ratio, 7.3 ±4.6 μm (R 1.6-29.5). Mean ISCC angle subtended from SC outer wall 9.5± 9.80 (R 0.0-51.7)
Conclusions :
CC extended a mean of 13.9 μm & a maximum of 28 μm into the sclera before abruptly turning circumferentially to join CVC. Flap-like relationships of collagen septum separated the SC and CVC lumens. CVCs coursed for a long distance nearly parallel to SC, consistent with MVC findings. The resultant long septa partition the CVC from SC and have a mean 100.4 μm thickness. The 7.3 mean septa aspect ratio mirrored that of the CVC. The elongated septa separate the CVC from SC, creating a noncontiguous separation of CC and distal radial channel lumens.
SEM confirms prior MVC of CVCs, the parallel outer channels adjacent to SC. Prior OCT motion studies demonstrate that CVCs experience pressure-dependent motion. The CVC can act as compressible conduits controlling the path of aqueous outflow. Improvements in canal-based MIGS depend on a better understanding of CVC relationships.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.