title: Aqueous outflow - A continuum from trabecular meshwork to episcleral veins.
abstract: In glaucoma, lowered intraocular pressure (IOP) confers neuroprotection. Elevated IOP characterizes glaucoma and arises from impaired aqueous humor (AH) outflow. Increased resistance in the trabecular meshwork (TM), a filter-like structure essential to regulate AH outflow, may result in the impaired outflow. Flow through the 360° circumference of TM structures may be non-uniform, divided into high and low flow regions, termed as segmental. After flowing through the TM, AH enters Schlemm's canal (SC), which expresses both blood and lymphatic markers; AH then passes into collector channel entrances (CCE) along the SC external well. From the CCE, AH enters a deep scleral plexus (DSP) of vessels that typically run parallel to SC. From the DSP, intrascleral collector vessels run radially to the scleral surface to connect with AH containing vessels called aqueous veins to discharge AH to blood-containing episcleral veins. However, the molecular mechanisms that maintain homeostatic properties of endothelial cells along the pathways are not well understood. How these molecular events change during aging and in glaucoma pathology remain unresolved. In this review, we propose mechanistic possibilities to explain the continuum of AH outflow control, which originates at the TM and extends through collector channels to the episcleral veins.
authors.affiliation: Department of Ophthalmology & Bascom Palmer Eye Institute, University of Miami, Miami, USA; Department of Biochemistry and Molecular Biology, University of Miami, Miami, USA.
authors.forename: Teresia
authors.initials: T
authors.lastname: Carreon
authors.affiliation: Department of Human Biology, Faculty of Health Sciences, University of Cape Town, Anzio Road, Observatory, 7925 Cape Town, South Africa.
authors.forename: Elizabeth
authors.initials: E
authors.lastname: van der Merwe
authors.affiliation: Glaucoma Associates of Texas, Dallas, TX, USA.
authors.forename: Ronald L
authors.initials: RL
authors.lastname: Fellman
authors.affiliation: Department of Ophthalmology, University of Washington, Seattle, WA, USA.
authors.forename: Murray
authors.initials: M
authors.lastname: Johnstone
authors.affiliation: Department of Ophthalmology & Bascom Palmer Eye Institute, University of Miami, Miami, USA; Department of Biochemistry and Molecular Biology, University of Miami, Miami, USA. Electronic address: sbhattacharya@med.miami.edu.
authors.forename: Sanjoy K
authors.initials: SK
authors.lastname: Bhattacharya
mesh_terms: D001082:Aqueous Humor / Q000378:metabolism*; D005901:Glaucoma / Q000378:metabolism / Q000503:physiopathology*; D006801:Humans; D007429:Intraocular Pressure / Q000502:physiology*; D012590:Sclera / Q000098:blood supply*; D014129:Trabecular Meshwork / Q000503:physiopathology*; D014680:Veins / Q000503:physiopathology*
keywords: Basement membrane: turnover and stability; Collector channels; Continuum hypothesis; Deep scleral plexus; Distal outflow; Glaucoma; Mechanosensing; Segmental outflow; Trabecular meshwork; schlemm's canal