Dielectric Spectroscopy (DES) is a non-invasive contact technique for the measurement of specific electrical properties of biological tissue induced by an external electric field. This method can also be used for in vivo measurements. The frequency of the electric field is varied up to 500 MHz. The permittivity, the relaxation time and the specific conductivity as a function of corneal hydration (wet weight/dry weight) and temperature are measured (10 porcine corneas). Variation of tissue hydration has a minor influence on the signal. Only for low hydration was a significant variation of the signal detectable. Much more influence was found when the tissue temperature increased. Dielectric spectroscopy has the potential to detect thermally induced structural changes of the tissue. DES has also been used for tissue discrimination and the measurement of hydration. It can measure the cornea's viscoelastic properties in vivo and distinguish normal skin from melanoma.
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