Background: An instrument to measure vibration in the middle ear needs to be sensitive enough to detect displacement on a nanometer scale, yet not affect the vibration itself. Numerous techniques have been described in the literature, but laser Doppler vibrometry (LDV) has nowadays become established as the standard method in hearing research.
Objective: This article aims to present possible clinical applications of an LDV system in otology.
Materials and methods: A commercially available single-point vibrometer was used. Measurements were carried out both with the sensor head mounted on an operating microscope and as a handheld device with the sensor head manually inserted in the ear canal. For the latter, a custom-made unit containing an electrically tunable lens was attached to the sensor head. Middle ear vibrations were measured in a temporal bone model as well as in patients during and after implantation of a Vibrant Soundbridge (VSB; MED-EL Corp., Durham/NC, USA).
Results: Different types of middle ear pathologies can be distinguished by the frequency response of the umbo. The LDV technique can be used for intraoperative quantification of the coupling quality of the VSB's Floating Mass Transducer (FMT; MED-EL) to the ossicle chain during VSB implantation. Postoperatively, the method serves as a follow-up testing tool if a deterioration in aided hearing threshold occurs. The measurement can reveal changes in the umbo transfer function, e. g., due to middle ear scarring or dislocation of the FMT.
Conclusion: Many clinical questions in otology can be addressed by LDV. However, due to the high acquisition costs of an LDV system, the relatively large instrumental setup, and the large inter-ear variability of middle-ear function, the technique has not (yet) become established in clinical routine.
Keywords: Implantable hearing aids; Middle ear; Mixed conductive-sensorineural hearing loss; Tympanic membrane; Vibration.