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Author Notes:

Corresponding author: Dr. Darryl R. Overby, Department of Bioengineering, Imperial College London, London SW7 2AZ, United Kingdom, +44 (0) 20 7594 6376, d.over@imperial.ac.uk

EM gratefully acknowledges support from the Royal Society and Royal Academy of Engineering; CRE gratefully acknowledges support from the Georgia Research Alliance.

Subjects:

Research Funding:

A grant from National Glaucoma Research, a Program of The BrightFocus Foundation (Formerly the American Health Assistance Foundation), and the National Eye Institute (EY019696, EY022359).

Keywords:

  • Science & Technology
  • Life Sciences & Biomedicine
  • Ophthalmology
  • Blood-aqueous barrier
  • Glaucoma
  • Schlemm's canal endothelium
  • Biological transport phenomena
  • Diffusion
  • TRABECULAR MESHWORK
  • INTRAOCULAR-PRESSURE
  • DIFFUSION-COEFFICIENTS
  • HUMOR OUTFLOW
  • INNER-WALL
  • PROTEINS
  • RESISTANCE
  • PATHWAYS
  • EYES
  • FLOW

Transport across Schlemm's canal endothelium and the blood-aqueous barrier

Tools:

Journal Title:

Experimental Eye Research

Volume:

Volume 146

Publisher:

, Pages 17-21

Type of Work:

Article | Post-print: After Peer Review

Abstract:

The majority of trabecular outflow likely crosses Schlemm's canal (SC) endothelium through micron-sized pores, and SC endothelium provides the only continuous cell layer between the anterior chamber and episcleral venous blood. SC endothelium must therefore be sufficiently porous to facilitate outflow, while also being sufficiently restrictive to preserve the blood-aqueous barrier and prevent blood and serum proteins from entering the eye. To understand how SC endothelium satisfies these apparently incompatible functions, we examined how the diameter and density of SC pores affects retrograde diffusion of serum proteins across SC endothelium, i.e. from SC lumen into the juxtacanalicular tissue (JCT). Opposing retrograde diffusion is anterograde bulk flow velocity of aqueous humor passing through pores, estimated to be approximately 5 mm/s. As a result of this relatively large through-pore velocity, a mass transport model predicts that upstream (JCT) concentrations of larger solutes such as albumin are less than 1% of the concentration in SC lumen. However, smaller solutes such as glucose are predicted to have nearly the same concentration in the JCT and SC. In the hypothetical case that, rather than micron-sized pores, SC formed 65 nm fenestrae, as commonly observed in other filtration-active endothelia, the predicted concentration of albumin in the JCT would increase to approximately 50% of that in SC. These results suggest that the size and density of SC pores may have developed to allow SC endothelium to maintain the blood-aqueous barrier while simultaneously facilitating aqueous humor outflow.

Copyright information:

© 2016 Elsevier Ltd. All rights reserved.

This is an Open Access work distributed under the terms of the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License (http://creativecommons.org/licenses/by-nc-nd/4.0/).

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