Measurement of the thickness of the tympanic membrane in cat using a heterodyne interferometer

摘要

The thickness of the tympanic membrane has to be known for the formulation of mathematical ear models. Using a commercial confocal laser scanning microscope we have found that the tympanic membrane has parts thinner than 10 micron. In this study we were forced to excise the tympanic membranes and due the restricted working distance of the microscope objective, we had to flatten the tympanic membrane onto a glass plate. Although we were able to measure thickness in fresh samples, thickness could still have been altered by the preparation procedure. S. Khanna developed over the years a powerful heterodyne interferometer with confocal pinholes in the illumination and observation arms. Thanks to its sectioning capabilities it can measure vibrations of structures embedded within other tissue without the need to expose the structure. While using this equipment in measuring vibrations in the middle ear, the idea grew that the interferometer could also be used to measure thickness, by tracking the carrier level of the interferometer while the laser focus is driven through the membrane. The method looks full of promises as measurements on animals with the tympanic membrane still in its original niche are possible without a prior preparation of the membrane.