April 2014
Volume 55, Issue 13
Free
ARVO Annual Meeting Abstract  |   April 2014
Viscoelastic Characterization of the Corneal Stroma assessed Ex Vivo using Atomic Force Microscopy
Author Affiliations & Notes
  • Janice Dias
    Dept. of Biomedical Engineering, University of Miami, Coral Gables, FL
  • Noel Marysa Ziebarth
    Dept. of Biomedical Engineering, University of Miami, Coral Gables, FL
  • Footnotes
    Commercial Relationships Janice Dias, None; Noel Ziebarth, None
  • Footnotes
    Support None
Investigative Ophthalmology & Visual Science April 2014, Vol.55, 3708. doi:
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      Janice Dias, Noel Marysa Ziebarth; Viscoelastic Characterization of the Corneal Stroma assessed Ex Vivo using Atomic Force Microscopy. Invest. Ophthalmol. Vis. Sci. 2014;55(13):3708.

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

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Abstract

Purpose: To quantify the viscoelasticity of the corneal stromal via stress relaxation and nanoindentation.

Methods: Experiments were conducted on five porcine eyes (3 eyes to measure stromal surface and 2 eyes to measure at a depth of 200µm; <3 days postmortem). The eyes were retrieved from an abattoir, placed in a bag filled with saline, and shipped to the laboratory overnight. Upon arrival, the epithelium was removed using a cotton swab, and the cornea was excised with a generous scleral rim and placed in 20% Dextran overnight to restore the cornea to physiological levels. Since the porcine cornea does not have Bowman’s membrane, no excisions were performed on corneas reserved for testing the stromal surface. A Moria microkeratome with a CBSU 200µm head was used to expose the mid-anterior stroma. All corneas were mounted on a custom chamber and immersed in 15% Dextran to maintain hydration. A custom-built Atomic Force Microscope (AFM) designed for the mechanical testing of ophthalmic tissues was used to perform stress relaxation. Spherically-tipped AFM cantilevers (diameter: 60-75µm) were used to indent the stromal surface approximately 2µm. This depth was held constant for a 2 minute duration as the resultant force response was recorded 2 times per sample. Young’s modulus of elasticity was calculated by fitting the force-displacement curve during indentation to the Hertz model. Apparent viscosity was calculated by fitting the force response during the 2 minute hold period to a modified standard linear solid viscoelastic model using MATLAB.

Results: The corneal thickness range was 671-705µm. The superficial anterior stroma had a Young’s modulus range of 391.5kPa-1.53MPa and apparent viscosity of 1.16-1.32MPa-s. The CBSU 200µm microkeratome head produced stromal cuts of 190µm and 237µm. At such depths, the stroma exhibited Young’s moduli of 178.3kPa and 864.4kPa, respectively and apparent viscosities of 0.197MPa-s and 0.178MPa-s, respectively. The apparent viscosities between the superficial and mid-anterior stromal surfaces exhibited a significant statistical difference (p<0.01).

Conclusions: The elastic and viscoelastic properties of the corneal stroma change at different stromal depths, becoming more elastic and less viscous at increased depths.

Keywords: 480 cornea: basic science  
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