April 2011
Volume 52, Issue 14
Free
ARVO Annual Meeting Abstract  |   April 2011
Characterization of Ocular Tissues Using Micro-Indentation and Hertzian Viscoelastic Models
Author Affiliations & Notes
  • Lawrence H. Yoo
    Ophthalmology, Chemistry and Biochemistry,
    Jules Stein Eye Institute, Los Angeles, California
    UCLA, Los Angeles, California
  • Jason Reed
    Ophthalmology, Chemistry and Biochemistry,
    UCLA, Los Angeles, California
    California NanoSystems Institute, Los Angeles, California
  • Andrew Shin
    Mechanical Engineering, Biomedical Engineering,
    Jules Stein Eye Institute, Los Angeles, California
    UCLA, Los Angeles, California
  • Jennifer S. Kung
    Ophthalmology, Chemistry and Biochemistry,
    Jules Stein Eye Institute, Los Angeles, California
    UCLA, Los Angeles, California
  • James K. Gimzewski
    Ophthalmology, Chemistry and Biochemistry,
    UCLA, Los Angeles, California
    California NanoSystems Institute, Los Angeles, California
  • Vadims Poukens
    Ophthalmology, Chemistry and Biochemistry,
    Jules Stein Eye Institute, Los Angeles, California
    UCLA, Los Angeles, California
  • Robert A. Goldberg
    Ophthalmology, Chemistry and Biochemistry,
    Jules Stein Eye Institute, Los Angeles, California
    UCLA, Los Angeles, California
  • Ronald Mancini
    Ophthalmology, Chemistry and Biochemistry,
    Jules Stein Eye Institute, Los Angeles, California
    Ophthalmology, UT Southwestern Medical Center, Dallas, Texas
  • Mehryar Taban
    Ophthalmology, Chemistry and Biochemistry,
    Jules Stein Eye Institute, Los Angeles, California
    UCLA, Los Angeles, California
  • Joseph L. Demer
    Ophthalmology, Chemistry and Biochemistry,
    Mechanical Engineering, Biomedical Engineering,
    Jules Stein Eye Institute, Los Angeles, California
    UCLA, Los Angeles, California
  • Footnotes
    Commercial Relationships  Lawrence H. Yoo, None; Jason Reed, None; Andrew Shin, None; Jennifer S. Kung, None; James K. Gimzewski, None; Vadims Poukens, None; Robert A. Goldberg, None; Ronald Mancini, None; Mehryar Taban, None; Joseph L. Demer, None
  • Footnotes
    Support  NIH Grant EY08313 and EY00331
Investigative Ophthalmology & Visual Science April 2011, Vol.52, 6369. doi:https://doi.org/
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      Lawrence H. Yoo, Jason Reed, Andrew Shin, Jennifer S. Kung, James K. Gimzewski, Vadims Poukens, Robert A. Goldberg, Ronald Mancini, Mehryar Taban, Joseph L. Demer; Characterization of Ocular Tissues Using Micro-Indentation and Hertzian Viscoelastic Models. Invest. Ophthalmol. Vis. Sci. 2011;52(14):6369. doi: https://doi.org/.

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

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Abstract

Purpose: : Accurate biomechanical properties of ocular tissues must be known to understand their mechanical interactions, yet classical tensile testing techniques are impractical for the small and irregular specimens typically available. We applied a novel micro-indentation technique to characterize biomechanical properties of small ocular and orbital tissue specimens using the Hertzian viscoelastic formulation, which defines material viscoelasicity in terms of contact pressure imposed during indention by a hard sphere.

Methods: : We employed a load cell with 100 nm displacement and 100 µg force precision to indent, with fine stainless steel spheres, fresh (<2 hrs post-mortem) specimens of bovine sclera, iris, crystalline lens, kidney fat, orbital pulley tissue, and orbital fat. We also studied fresh (<30 min post-excision) specimens of normal human orbital fat, eyelid fat, and dermal fat, and orbital fat associated with thyroid eye disease. Stress relaxation testing was performed using multiple initial indentation rates. Results for single indentations were used to fit quantitative Hertzian viscoelastic models that were in turn compared with behavior for other indentations and indentation rates. Findings in orbital tissues were correlated with quantitative histological determinations of connective tissue content.

Results: : Viscoelastic properties of small specimens of orbital and ocular tissues were reliably characterized over a wide range of rates and displacements by microindentation using the Hertzian formulation. While orbital fatty tissues exhibited highly similar elastic and viscous behaviors whether from bovine or human sources, different orbital tissues within species exhibited widely varying biomechanical properties. Since stiffness of fatty tissues was highly correlated with connective tissue content, orbital pulley tissues were much stiffer than orbital fat.

Conclusions: : Relaxation testing by microindentation is a powerful method for characterization of time-dependent behaviors of a wide range of ocular and orbital tissues using small specimens, and provides data suitable to define finite element models of a wide range of mechanical interactions within ocular tissues.

Keywords: eye movements • sclera • iris 
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