September 2016
Volume 57, Issue 12
Open Access
ARVO Annual Meeting Abstract  |   September 2016
IOP-induced Changes in Schlemm’s Canal Dimensions and the Relation to Shear Stress
Author Affiliations & Notes
  • Nicole E Ashpole
    Biomedical Engineering, Duke University, Durham, North Carolina, United States
  • Dibyendu Mukherjee
    Biomedical Engineering, Duke University, Durham, North Carolina, United States
  • Guorong Li
    Ophthalmology, Duke University, Durham, North Carolina, United States
  • Paolo Maccarini
    Biomedical Engineering, Duke University, Durham, North Carolina, United States
  • Joseph M. Sherwood
    Biomedical Engineering, Imperial College, London, United Kingdom
  • C Ross Ethier
    Biomedical Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States
  • Darryl R Overby
    Biomedical Engineering, Imperial College, London, United Kingdom
  • Sina Farsiu
    Biomedical Engineering, Duke University, Durham, North Carolina, United States
    Ophthalmology, Duke University, Durham, North Carolina, United States
  • W Daniel Stamer
    Ophthalmology, Duke University, Durham, North Carolina, United States
    Biomedical Engineering, Duke University, Durham, North Carolina, United States
  • Footnotes
    Commercial Relationships   Nicole Ashpole, None; Dibyendu Mukherjee, None; Guorong Li, None; Paolo Maccarini, None; Joseph Sherwood, None; C Ethier, None; Darryl Overby, None; Sina Farsiu, None; W Stamer, None
  • Footnotes
    Support  National Institute of Health (Grant #EY017007 and #EY022359)
Investigative Ophthalmology & Visual Science September 2016, Vol.57, 6418. doi:
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    • Get Citation

      Nicole E Ashpole, Dibyendu Mukherjee, Guorong Li, Paolo Maccarini, Joseph M. Sherwood, C Ross Ethier, Darryl R Overby, Sina Farsiu, W Daniel Stamer; IOP-induced Changes in Schlemm’s Canal Dimensions and the Relation to Shear Stress. Invest. Ophthalmol. Vis. Sci. 2016;57(12):6418.

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      © ARVO (1962-2015); The Authors (2016-present)

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Abstract

Purpose : In vascular endothelia including Schlemm's canal (SC), nitric oxide (NO) is produced by endothelial NO synthase (eNOS), whose activity and abundance are regulated by shear stress. In simplified elliptical models of SC, wall shear stress (WSS) at elevated intraocular pressures (IOP) is calculated to be comparable to those in large arteries. Using spectral-domain optical coherence tomography (OCT) imaging of living mice, we create more realistic 3D models of SC to estimate WSS and thus investigate the relationship between IOP and shear stress.

Methods : IOP was controlled by intracameral cannulation of anesthetized (ketamine/xylazine, intraperitoneal injection) C57BL/6 mice (6 months old), while simultaneously imaging iridocorneal angle structures using OCT (Envisu R2200, 2 µm resolution, Bioptogen, Inc). Incremental sagittal OCT sections along a 0.2 mm length of SC were acquired at two IOPs (10 and 15 mmHg), to create a stack of images (0.0085 mm distance between image slices). Customized software (Matlab) was used to segment SC on each OCT image, which was easily visualized at the two selected IOPs. A 3D SC replica consisting of SC and 2 collector channels was built using Aviso (FEI) and ANSYS software (ANSYS, Inc.).

Results : When changing IOP in living mice from 10 to 15 mmHg the SC lumen imaged by OCT reduced by 43% on average from an integrated volume of 13.8 ± 5.8 µm3 to 7.8 ± 4.8 µm3. This corresponds to a decrease in SC height from 6.7 µm to 3.8 µm based on previous elliptical models.

Conclusions : IOP elevation from 10 to 15 mmHg decreases SC volume, corresponding to a pressure-dependent decrease in SC height (inner-outer wall separation). Previous elliptical models suggest that this change will lead to an increase in shear stress to levels capable of increasing eNOS activity (~2 dynes/cm2). In conjunction with computational fluid dynamics, our new 3D model of SC at both 10 and 15 mmHg will enable analysis of the fluid flow and estimation of wall shear stress in Schlemm’s Canal.

This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.

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