Abstract
In this study, dynamic mechanical analysis (DMA) was utilized for the measurement of the viscoelastic properties of human cornea. The complex shear compliance J (reciprocal shear modulus G), Young’s compliance D (reciprocal Young’s modulus E), and the “indenter compliance” C were recorded as a function of frequency (spectrum), of time, of hydration and of temperature.
The viscoelasticity spectra revealed three different relaxation processes within the frequency range of twelve decades (0.1 mHz to 100 MHz). The parameters of these relaxation processes (relaxation frequency, relaxation strength, width-parameter) are affected by hydration, temperature (thermal softening, thermal coagulation, freezing), post mortem-interval, and pathological changes. Comparing Young’s modulus E⊥ (perpendicular to the corneal surface) and its correlated shear modulus G, we found E⊥ ≈ 100G (at 1 Hz). This reflects the cornea’s structural anisotropy and the experience that a cornea is easy to shear but hard to compress.
The spectra of indenter compliance C(f) were similar to the shear compliance spectra J(f), i.e., indentation (like induced by an applanation tonometer) causes a shear deformation rather than a compression of the cornea.
Newly developed DMA set-ups for non-destructive characterization of eye bank eyes and for diagnosing non-physiological and pathological changes of the cornea in vivo, are in the experimental stage now.
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Soergel, F., Muecke, S., Pechhold, W. (1997). Corneal Viscoelasticity Spectra as a Result of Dynamic Mechanical Analysis. In: Lass, J.H. (eds) Advances in Corneal Research. Springer, Boston, MA. https://doi.org/10.1007/978-1-4615-5389-2_25
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DOI: https://doi.org/10.1007/978-1-4615-5389-2_25
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