Laser-Doppler vibrometer–based measurement system, consisting of a helium-neon laser, controlling hardware, and a joystick-controlled aiming prism. Both the laser and the prism are mounted on a standard operating microscope, allowing the clinician observer to see and focus the laser at a point in the viewing field. The laser and the microscope are confocal. A standard stainless Steel speculum couples to the glass-backed sound coupler with attachments for a sound source and a probe tube microphone The long nylon probe tube is threaded through the coupler and terminates approximately 5 mm beyond the speculum tip. The clinician places the coupler/speculum so as to view the umbo and the light reflex. The laser is then positioned on the naturally reflective light reflex to get adequate reflected light back to the sensor in the laser assembly. A too-low reflectivity leads to poor signal to noise on the laser channel.

Sound stimulus and laser response spectra from a typical measurement. The sound pressure of the total stimulus was 88 dB SPL. Left, spectrum of the stimulus sound pressure. Right, spectrum of the velocity response. The frequency resolution of each spectrum is 100 Hz. Spectrum lines with magnitudes less than the minimum value of the ordinates are not plotted. Spectral lines at the nine stimulus frequencies are marked with circles. The noise estimate is created by connecting the lines at the nonstimulus frequencies. The noise about each stimulus frequency is determined by averaging the nonstimulus lines adjacent to the stimulus frequencies. Whereas the noise in the sound pressure stimulus was low throughout, the noise in the velocity response signal varied from measurement to measurement depending on the stability of the subject’s head and the amount of light reflected back to the laser during the measurement.

Comparison of the means and variance of the patient groups with the normal group. The four curves in each panel represent the mean magnitude and angle in four measurements groups: normal ears (n = 73), fixed stapes (n = 12), ossicular interruption (n = 4) and fixed malleus (n = 1). The shaded area shows the range of the normal measurements. The bars are the 95% confidence limits (1.95 times the standard error of the mean) about the means. Small or no overlaps between the means and confidence limits indicate significant differences between the populations.

Magnitude and angle of umbo velocity transfer functions in ears after successful small fenestra stapedectomy with a 0.6 mm piston. A, Comparison of laser-Doppler vibrometry (LDV) measurements in the 10 individual post-stapedectomy cases with the mean, 95% confidence interval, and range of normal measurements. B, Comparison of the mean ± 95% confidence limits in normal subjects, poststapedectomy patients, and ossicular interruption patients.

Comparisons of laser-Doppler vibrometry (LDV) changes and air-bone gaps in three cases with different ossicular pathologic features. The left-hand ordinates scale the ratio of the magnitude of the umbo velocity measured in the individual ear to the normal mean magnitude. This ratio is plotted with open circles for different individual cases in the three panels. The right-hand ordinates scales presurgical air-bone gaps (plotted with Xs) in the same ears. The three cases include fixed stapes, fixed malleus and incus, and an erosion of the bony incus with a resultant fibrous union of the incus and stapes heads.

Magnitude and angle of umbo velocity transfer functions in normal ears and two patient populations. The transfer function is defined as the ratio of the laser-Doppler vibrometry (LDV) measured velocity near the umbo and the sound pressure measured near the tympanic membrane by the probe microphone. The upper plot of each panel shows the transfer function magnitude in units of mm/s/Pa (velocity/sound pressure). The lower plot shows the angle of the transfer function, which is equivalent to the phase of the velocity minus the phase of the sound pressure. Positive angles occur when the velocity leads the sound pressure; negative angles occur when the velocity lags the sound pressure. A, Normal ears. The measured transfer function in 73 individual ears with no air-bone gaps are illustrated along with the mean and the 95% confidence interval (± 1.96 times the standard error) around the mean. B, Confirmed ossicular fixations. The LDV results from 12 ears with surgically confirmed fixed stapes (due to otosclerosis) and one ear with fixed malleus and incus head (due to fibrous adhesions in the epitympanic cavity) are compared with the mean and range of the normal population. Measurements in the 12 fixed stapes cases fall within the normal range but are generally lower than the normal mean magnitude and have angles that are more positive than the normal mean. The one case of malleoincudal fixation has a velocity magnitude that is as much as a factor of 4 (12 dB) smaller than the lowest normal measurements and an angle that is generally more positive than the normal mean. C, Partial and complete ossicular interruptions. LDV results from four ears with surgically confirmed ossicular interruptions (one complete interruption at the neck of the malleus and 3 cases of erosion of the bone of the incus resulting in a fibrous attachment of the incus and stapes head) are compared with the mean and range of the normal population. These four cases have low-frequency velocities that are larger than the normal range and high-frequency magnitudes that are generally smaller than the normal mean. The angles of the four interruption cases are more negative than the normal mean but generally fall within the normal range.