Skip to main content
. Author manuscript; available in PMC: 2021 Jul 21.
Published in final edited form as: Prog Retin Eye Res. 2020 Nov 17;83:100917. doi: 10.1016/j.preteyeres.2020.100917

Fig. 21. Provisional 2D outflow model for regulation of homeostasis.

Fig. 21.

(A), (B), and (C) depict cross-sections through the outflow system while (D), (E) and (F) show global motion in three dimensions (3-D). Aqueous passes through the TM to the juxtacanalicular space (JCS). From the JCS, aqueous flows through the Schlemm’s canal (SC) inlet valves into SC. SC outlet valves (SOV), consisting of hinged collagen flaps, control collector channel entrance (CCE) dimensions. As Intraocular pressure (IOP) increases from low in (A-D) through the setpoint (B-E) to high in (C-F), the intertrabecular spaces and JCS enlarge, and SC narrows. In a 3-D view, the SIV, attached both to the TM and SOV, are oriented circumferentially in SC. Outward movement thus pulls the SOV open. (B-E) envisions an IOP of 16 mm Hg as an ideal homeostatic setpoint configuration. As IOP increases in (C-F), the TM moves outward. The SIV experience increased tension, resulting in increased stress on the SOV, causing it to open the CCE further. The CCE enlargement causes increased aqueous flow; IOP then falls with an associated inward movement of the TM, restoring it to the setpoint of (B-E). At a low IOP as in (A-D), the CCE is closed, reducing flow. Reduced flow increases IOP causing the TM to distend, thereby returning tension to the setpoint in (B-E). IOP generates forces causing TM tissues to deform and distend into SC. TM elastance properties balance the distending or loading force of IOP. TM tissues at the homeostatic setpoint are in an IOP-induced, prestressed, equilibrium state of deformation. Under homeostatic conditions of IOP > SCP > EVP, gradients favor closure of the HCF because SCP is higher than EVP. TM tension on the SOV, causes them to enlarge and optimizes CCE dimensions. Blue arrows in CCE depict changes in the rate of flow. Black arrow points to CCE. The proposed model is offered for consideration but is unproven, and its premises are subject to modification or rejection as new evidence emerges. From Johnstone M, IOP control through linked trabecular meshwork and collector channel motion. Glaucoma Research and Clinical Advances: 2016 to 2018. Kugler Publications, Amsterdam.