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Nystagmographs and Movies of the head positioning nystagmus of the new variant of BPPV recorded during the D-H method (Case 6 in Table 1). Head positioning from the upright sitting position to the right D-H head position (left, Movie 1); head positioning from the right D-H head position to the upright sitting position (right, Movie 2); horizontal eye movement (top); vertical eye movement (middle); and torsional eye movement (bottom). The direction of torsional nystagmus is the side of the ear toward which the upper pole of the eye rotates. ↓ indicates immediately after head positioning. In the right D-H head position, downbeating-torsional nystagmus toward the left side is observed with a latency of 4 seconds. The nystagmus gradually attenuates and disappears. The nystagmus duration is approximately 15 seconds. The maximum slow-phase velocities of nystagmus are 5.9°/s (downward) and 4.8°/s (torsional). In the upright sitting position, intense upbeating-torsional nystagmus toward the right side is observed with a latency of 4 seconds. The nystagmus gradually increases, attenuates, and disappears. The nystagmus duration is approximately 23 seconds. The maximum slow-phase velocities of nystagmus are 18.5°/s (upward) and 7.1°/s (torsional).
The Figure shows the nystagmus direction due to the right posterior semicircular canal and right anterior semicircular canal based on Ewald's first law (some illustrations are modified from ). We can observe nystagmus as the movement of the front of the eyeballs. These two can be easily distinguished by observing the direction of the arc-shape projection of the rotatory component. When the arc-shape projection is directed to the healthy side, nystagmus should originate from the posterior semicircular canal. When the arc-shape projection is directed to the affected side, nystagmus should originate from the anterior semicircular canal.
Published online: February 19, 2021
© 2020 Japanese Society of Otorhinolaryngology-Head and Neck Surgery, Inc. Published by Elsevier B.V. All rights reserved.
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