Handheld laser-fiber vibrometry probe for assessing auditory ossicles displacement

Measurements of auditory ossicles displacement are commonly carried out by means of laser-Doppler vibrometry (LDV), which is considered to be a gold standard. The limitation of the LDV method, especially for in vivo measurements, is the necessity to expose an object in a straight line to a laser beam operating from a distance. An alternative to this approach is the use of a handheld laser-fiber vibrometry probe (HLFVP) with a curved tip.

We evaluate the feasibility of an HLFVP with a curved tip for measuring sound-induced displacement of the auditory ossicles.

A handheld vibrometer probe guiding the laser beam with a fiber-optic cable was used for displacement measurements of the incus body and the posterior crus of the stapes. Tonal stimuli at frequencies of 0.5, 1, 2, and 4 kHz were presented by means of an insert earphone positioned in the outer ear canal. The probe was fixed at the measurement site using a tripod or hand-held by one of the two surgeons.

The measurements were carried out on six fresh temporal bones. Multivariate analysis of variance showed statistically significant differences for stimulus frequency (F3,143  =  29.37, p  <  0.001, and η2  =  0.35), bone (F5,143  =  4.61, p  =  0.001, and η2  =  0.01), and measurement site (F1,143  =  4.74, p  =  0.03, and η2  =  0.02) in the absence of statistically significant differences for the probe fixation method (F2,143  =  0.15, p  =  0.862, and η2  =  0.001). Standard deviations of the means were 6.9, 2.6, 1.9, and 0.6  nm  /  Pa for frequency, bone, site, and fixation, respectively. Ear transfer functions were found to be consistent with literature data.

The feasibility of applying HLFVP to measure the displacement of auditory ossicles has been confirmed. HLFVP offers the possibility of carrying out measurements at various angles; however, this needs to be standardized taking into account anatomical limitations and surgical convenience.