Question

In head impulse test, following finding seen in right vestibular neuritis:

• A. On rotating head to right, left saccade
• B. On rotating head to left, right saccade
• C. On rotating head toward right, right saccade
• D. On rotating to the left, left saccade

Hint:

Turning the head toward the diseased side reveals a corrective catch-up saccade in the OPPOSITE direction. Right neuritis: turn right, saccade left.

Answer 1

The Correct Option is A

Step 1: Understand the head impulse (head thrust) test and the VOR. The vestibulo-ocular reflex (VOR) keeps the eyes fixed on a target while the head moves: when the head turns one way, the eyes must move equally and oppositely. The HORIZONTAL canal on the side TOWARD which you turn the head is the one being tested (Ewald's first law - the horizontal canal is excited by ipsilateral head rotation).
Step 2: Apply it to right vestibular neuritis. Right vestibular neuritis causes a hypofunctioning RIGHT horizontal semicircular canal/right vestibular nerve. When the examiner rapidly turns the patient's head TO THE RIGHT, the weak right canal cannot generate an adequate VOR, so the eyes are dragged off-target (they move with the head toward the right).
Step 3: The corrective saccade. Because the eyes overshoot toward the right (off the target), the brain must bring them BACK onto the target with a rapid corrective (catch-up) saccade in the opposite direction - to the LEFT. This visible leftward refixation saccade after a rightward head thrust is the positive (abnormal) result and localises the lesion to the RIGHT side.
Step 4: Why option A is correct and others wrong. (A) On rotating head to right, left saccade = turning toward the diseased right side reveals a corrective leftward saccade - correct. (B) Turning to the left tests the healthy LEFT canal, which works, so no saccade - wrong. (C) The saccade is corrective and must go OPPOSITE to the head turn (left), not to the right - wrong. (D) Turning left tests the normal side; no corrective saccade is expected - wrong.
Final answer: A. On rotating head to right, left saccade.