The use of Laser Doppler vibrometry (Doppler principle) for middle ear research and diagnosis

The middle ear represents the middle component of the human ear. Its function is to transmit sound-waves from the external auditory canal (EAC) to the inner ear via the Tympanic Membrane (TM), the Ossicular Chain (OC), and Oval Window (OW) and at the same time to act as a transformer that produces a pressure gain in the sound wave, usually specified in literature as 27-30 dB. Although a very efficient biomechanical system, the OC has, within the human hearing range, minute vibration amplitudes of only a few nm which brings forward the problem of a reliable measuring technique for such movements The Laser Doppler Vibrometry (LDV) also known as Laser Doppler Interferonometry (LDI) is a method of measuring such minute vibrations without contact with the anatomical structures. The laser beam can be aimed at chosen points of a structure and the movement will be recorded as a graphical representation. As such, the method has been studied and applied for numerous purposes and experiments over the last decades. The present work aims to present a comprehensive review of these experiments to define LDV as a reliable method for middle ear research and diagnostics.