Describe typical nystagmus findings in unilateral vestibular hypofunction with the patient looking straight ahead.

• A. Spontaneous horizontal nystagmus beating away from the lesioned side; reduced VOR gain on the affected side.
• B. Upbeat torsional nystagmus toward the lesioned side.
• C. No nystagmus at all; normal VOR.
• D. Pure vertical nystagmus with fast phase downward.

Answer: (D)

Unilateral vestibular hypofunction creates an imbalance in tonic vestibular input between the two ears. When a person looks straight ahead, the brain relies on symmetrical input to keep gaze stable. The reduced input from the lesioned side causes the eyes to drift slowly toward that side, with a quick corrective saccade beating in the opposite (healthy) direction. This produces a spontaneous horizontal nystagmus whose fast phase points away from the lesioned side, and the VOR gain is reduced on the affected side because the corresponding vestibular signal is diminished.

So the typical finding is a horizontal nystagmus beating away from the damaged ear, with reduced VOR gain on the side of the lesion. The other patterns described—upbeat torsional nystagmus, no nystagmus, or pure vertical downward fast phase—do not fit the common horizontal nystagmus and reduced VOR associated with unilateral hypofunction when gaze is straight ahead; they suggest different or central involvement or non-typical peripheral patterns.