PMC8692282_01
Right and left pure tone air-conduction audiograms from the last 3 years. Unilateral right fluctuating low and mid-frequencies hearing loss with a PTA 40 dB-HL is present at testing in 2019, 2020, and 2021 while normal hearing was obtained in left ear on these occasions with a PTA of 20 dB-HL. Hearing loss levels and PTA calculation methods according to BIAP 2017 (www.biap.org).
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F1
During the last 5 years she reported unilateral right fluctuating low and had mid-frequency hearing loss (Figure 1) with mild sensorineural hearing loss of the right ear (PTA 40 dB-HL). Figure 1 shows that at the end of each rightward head impulse there was a corrective saccade which acted to eliminate the gaze position error caused by the enhanced eye velocity and so this saccade is compensatory. As is clear from Figure 1, saccades rarely occurred during the rightward head turn, so desaccading was not required for VOR gain calculation. These corrective saccades after ACQEMs are clearly shown in Heuberger Figure 1. It has been suggested that this could be due to the very different eye velocity trajectories during the increasing head velocity and decreasing head velocity phases of the head impulse [Curthoys et al.; Figure 1]. It may be that the eye position error during the acceleration phase may be partially corrected by the eye position error during the deceleration phase, resulting in such a small final eye position error that it is not necessary for any correction.
Rightward video head impulse test responses performed during the patient's most recent test (2021). The eye velocity (orange) is enhanced compared to head velocity (blue). This will result in the eye being off target and in order to correct that gaze position error (Figure 4) the eye makes a compensatory backup saccade. (A) All the right-side impulses are plotted with backup saccades present on all impulses. (B) A single rightward head impulse to show the onset of the backup saccade exactly.
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F2
VOR gains for the right were >1) (Figure 2, Supplementary Video 2). VOR gain was calculated using the area under the desaccaded eye velocity record divided by the area under the head velocity curve for VOR gain measurement as is standard for the ICS Impulse system. They act to correct the gaze position error entailed by enhanced eye velocity during the head impulse (Figures 2, 4).
Time series of head and eye velocity during the visual vestibular-ocular (VVOR) interaction test at 1.84 Hz. There is evidence of enhanced eye velocity for rightward head turns and backup saccades are present in each rightward head turn. Normal eye velocity responses occur for leftward head rotations. In this VVOR figure, negative velocity values are assigned to right direction movement velocity. The VOR gain for the right and left sides were 1.07 and 0.91, respectively.
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F3
This patient also showed backup saccades during rightward head movements in low frequency visual vestibular (VVOR) testing (Figure 3) at a frequency of 1.84 Hz.
Time series plots of eye velocity and corresponding eye position during a single rightward head impulse to show how the backup saccade corrects for the gaze position error. In (A), the enhanced eye velocity (red shadow brush) is followed at the end of the head impulses by a backup saccade (black shadow brush). In (B), head and eye position during the impulse are plotted. The dashed line shows eye position without backup saccade.
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F4
That result is very clearly shown by the eye position records (Figure 4). They act to correct the gaze position error entailed by enhanced eye velocity during the head impulse (Figures 2, 4).