What best distinguishes spontaneous nystagmus from gaze-evoked nystagmus?

• A. Spontaneous nystagmus occurs without fixation; gaze-evoked appears with eccentric gaze due to central pathology and may persist
• B. Spontaneous occurs only with fixation; gaze-evoked occurs only at rest
• C. Spontaneous nystagmus is always vertical; gaze-evoked is always horizontal
• D. Spontaneous nystagmus is a central sign; gaze-evoked is peripheral

Answer: (A)

Spontaneous nystagmus is an involuntary eye movement that appears at rest in the primary gaze, signaling an imbalance in vestibular input. It is seen without intentionally shifting the gaze, and its presence reflects the baseline drift and corrective fast phase produced by that imbalance. Gaze-evoked nystagmus, on the other hand, shows up when the eyes are held in an eccentric (off-center) gaze. It arises because the neural integrator that holds the eyes steady is impaired—typically from a central lesion—and the nystagmus can persist even after returning to center due to the leaky gaze-holding system. So the key distinction is when the nystagmus occurs and whether it can persist: spontaneous nystagmus is in primary position and tied to a vestibular imbalance, while gaze-evoked nystagmus is elicited by eccentric gaze and may persist because of central pathology.