Which scenario BEST indicates a unilateral lesion of the semicircular canals on the right side during head thrust testing?

Which scenario BEST indicates a unilateral lesion of the semicircular canals on the right side during head thrust testing?

• A. Able to maintain gaze when head rotated left
• B. Able to maintain gaze when head rotated right
• C. Unable to maintain gaze when head rotated left
• D. Unable to maintain gaze when head rotated right

Answer: (D)

In head thrust testing, the vestibulo-ocular reflex keeps your eyes on a fixed target during quick head turns. If one side’s horizontal semicircular canal is damaged, turning the head toward that lesioned side cannot produce enough eye movement to compensate, so the eyes slip with the head and a rapid corrective saccade is needed to re-fixate. With a right-sided lesion, turning the head to the right will fail to maintain gaze, producing that catch-up movement back to the target. Turning toward the left (the healthy side) is typically well compensated, so gaze is maintained. Therefore, the best indicator of a unilateral right canal lesion is an inability to maintain gaze when the head is rotated to the right.

In head thrust testing, the vestibulo-ocular reflex keeps your eyes on a fixed target during quick head turns. If one side’s horizontal semicircular canal is damaged, turning the head toward that lesioned side cannot produce enough eye movement to compensate, so the eyes slip with the head and a rapid corrective saccade is needed to re-fixate. With a right-sided lesion, turning the head to the right will fail to maintain gaze, producing that catch-up movement back to the target. Turning toward the left (the healthy side) is typically well compensated, so gaze is maintained. Therefore, the best indicator of a unilateral right canal lesion is an inability to maintain gaze when the head is rotated to the right.