Laser Doppler Scanning of the Vibrating Tympanic Membrane

Abstract

Among projects attributed to “Advances in Modern Otolaryngology” I would like to introduce a method for Laser Doppler Interferometric Scanning of the vibrating tympanic membrane (TM), developed at the ENT Department in Malmö, Sweden, in collaboration with Celestion International Limited, Ipswich, Suffolk, England, by Konrad Konradsson, Alf Ivarsson and Graham Banks. As a complement to the verbal description of the method and preliminary results hitherto obtained, I also want to present a video film showing TM vibrations at different frequencies and sound intensities. According to Helmholtz (2), the tympanic membrane acts as a transformer so that at a given sound pressure level the anterior and posterior parts of the drum shows a larger displacement than the central part, which is connected to the malleus. In 1941 G von Bekesy was able to measure vibrations of the tympanic membrane for the first time. He concluded that the TM vibrated like a stiff plate hinged superiorly around the ossicular axis of rotation. However, Tondorf & Khanna (5) found that the vibratory pattern of the TM was more complex. They used a method for average hollography. Thus, their findings were more in agreement with Helmholtz' original theory.