Tympanic membrane shape determined by moiré topography

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Abstract
Calculations of the modes of tympanic membrane (TM vibrations require knowledge of its shape. Moiré topography may be employed for determining such shapes. A parallel beam of light produces shadows of a Ronchi ruling on the object under study. When the object is then viewed (or photographed) through the ruling, contour lines are observed, each line representing one given height. The spacing between these lines depends on the number of lines/mm of the ruling, on the angle at which the object is being viewed with respect to the incident beam, and on the shape of the object. Contour lines of high contrast require the object to be placed very close to the ruling. Since this was impossible with the TM, silastic casts were made of the TM of cat and guinea pig. Their weight was less than 0.05 g and, therefore, did not appreciably alter the shape of the TM. The method of calibration and results of the measurements are discussed. [Supported by NIH grants.]

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