Nystagmus

Nystagmus is an involuntary, rhythmic oscillation of the eyes. Its direction, speed, and triggers help distinguish its causes and clinical forms.

Vestibulo-ocular reflex: A reflex that moves the eyes opposite to head motion, stabilizing images on the retina. Disruption or imbalance in this stabilizing reflex can produce oscillating eye movements.
Vestibular system: The inner-ear organs and neural pathways that sense head motion and orientation. Its signals are central to balance and to eye movements that stabilize vision during motion.
Congenital nystagmus: Nystagmus that begins in infancy, often associated with early disruption of visual development or inherited conditions. Early onset changes the likely causes and the effects on vision compared with newly acquired nystagmus.
Internuclear ophthalmoplegia: An eye-movement disorder caused by damage to the medial longitudinal fasciculus, impairing coordinated horizontal gaze. Its characteristic abducting-eye nystagmus accompanies a specific pattern of impaired horizontal eye movement.
Gaze-evoked nystagmus: Nystagmus that appears or intensifies when the eyes look away from their resting position. It reflects limits in the neural system that holds the eyes steadily in eccentric gaze.
Semicircular canals: Three fluid-filled inner-ear structures that detect rotational head movements. Their sensory signals drive eye responses that can become rhythmic when vestibular input is imbalanced.
Acquired nystagmus: Nystagmus that begins after infancy and may arise from vestibular, neurologic, medication-related, or visual causes. New onset can signal a disorder requiring prompt assessment, especially with other neurologic symptoms.
Ocular flutter: A rapid series of back-to-back horizontal saccades without an interval between movements. It is a saccadic oscillation, unlike nystagmus with alternating slow and fast phases.
Optokinetic nystagmus: A normal alternating eye movement elicited by a broad visual scene moving across the field of view. Its slow tracking and quick resetting phases illustrate how visual motion can generate nystagmus.
Smooth pursuit: A voluntary eye movement that tracks a moving object to keep its image near the fovea. Unlike nystagmus, pursuit follows a target continuously rather than alternating slow and fast phases.

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