SC has attracted considerable interest in recent years, due to the unique microstructure of the endothelial cells in the inner wall and its potential function in keeping IOP stable.
20,21 The aqueous humor flows through the conventional pathway, comprised of the trabecular meshwork and SC, and drains into the collecting channels and aqueous veins. Outflow resistance is mainly generated near SC, but the precise location and mechanism by which this dissipation occurs, remain a matter of contention. Some investigators have proposed that the resistance arises in the juxtacanalicular connective tissue (JCT) in particular, because of the abundant extracellular matrix and collagens.
22 However, the hydraulic conductivity, which reflects the flow resistance across the connective tissue, is extremely low in the JCT (about 65 × 10
−14 cm
2 as calculated by porous media theory
23 and 2000–10,000 × 10
−14 cm
2 based on photomicrographs
24). Accordingly, numerous investigators have concluded that the JCT would generate an insignificant fraction of outflow resistance.
23–26 The pores and giant vacuoles of the endothelium of the SC are also thought to modulate the aqueous humor outflow resistance.
27 In morphologic studies, mathematical modeling revealed that the dilation of SC led to an increased outflow facility.
28,29 By using a morphometric analysis system, Allingham et al.
30 found that the reduction in SC dimensions in eyes with primary open-angle glaucoma may account for approximately half of the decrease in the outflow facility. In our study, after the acute IOP elevation, there was a significant decrease in the SCAR, which was accompanied by a decrease in the outflow facility in the healthy subjects; however, the thickness of the trabecular meshwork remained unchanged. Changes in the SCAR from 0 to 4 minutes after the external pressure elevation, correlated significantly and positively with the outflow facility coefficient. Thus, reduction in SC area accounts for the decrease in the outflow facility in the healthy subjects in vivo.