Fig. 17. Schlemm’s canal outlet valves: Pressure-dependent appearance.

In vivo fixation, while maintaining an IOP in (A) of 0 and (B1–B3) of 25 mm Hg. Images in serial sections of (B1–B3) illustrate the transition from a collector channel entrance to a circumferentially oriented deep scleral plexus (CDSP). Hinged collagen flaps (HCF) at collector entrances (CCE) are free at one end. The HFC can move freely in response to TM movement induced by pressure changes, thus permitting them to have a pressure-dependent valve-like function at CCE. In (B2 and B3), a long septum (S) separates SC from a circumferentially oriented deep scleral plexus (CDSP). In (A and C), a HCF is far from the corneoscleral wall (CSW) of SC. The next serial section, not shown but depicted in C, contains a transcanalicular attachment extending from the TM to the tip of the HCF. In image (B1), the hinged collagen flap at the entrance to a CCE is in apposition (App) to the CSW. Collagen fibers at the base of the hinge in (B1–B3) are circular running orthogonal to the plane of section, but are parallel in the hinged septum, providing a pivot point for motion. Septa dividing SC from CDSP are collagenous structures and differ from the aqueous valves that are transcanalicular endothelial-lined conduits spanning SC. Features of images (C and D), derived from (A) and (B), are color-coded as follows: Red, blood, blue, aqueous; green, hinged collagen flap; yellow, cylindrical attachments connecting to TM. Note blood in (B1) and (D) distal to the HCF. The apposition of the HCF to SC external wall prevents blood from entering the canal. (E) Ex vivo fixation of human eye at IOP of 50 mm Hg with TM distending or herniating into SC at a CC entrance at a fusiform dilation (FD) of SC external wall. A long HCF is present at the CC entrance. Tissue source: Primate, Macaca mulatto. From Johnstone, Howe Laboratory of Ophthalmology, Harvard Medical School 1972. Video - CC Open and Close 1-s2.0-S1350946220300896-mmc7.mp4.