What is "nystagmus"

Nystagmus \Nys*tag"mus\, n. [NL., fr. Gr. ? drowsiness, fr. ? to nod in sleep, to slumber.] (Med.) A rapid involuntary oscillation of the eyeballs.

medical Latin, from Greek nystagmos "nodding, drowsiness," from nystazein "to nod, be sleepy," from PIE *sneud(h)- "to be sleepy."

n. rapid involuntary eye movement, usually lateral

n. involuntary movements of the eyeballs; the presence or absence of nystagmus is used to diagnose a variety of neurological and visual disorders

Nystagmus is a condition of involuntary (or voluntary, in rare cases) eye movement, acquired in infancy or later in life, that may result in reduced or limited vision. Due to the involuntary movement of the eye, it is often called "dancing eyes".

In a normal condition, while the head rotates about any axis, distant visual images are sustained by rotating eyes in the opposite direction on the respective axis. The semicircular canals in the vestibule sense angular acceleration. These send signals to the nuclei for eye movement in the brain. From here, a signal is relayed to the extraocular muscles to allow one’s gaze to fixate on one object as the head moves. Nystagmus occurs when the semicircular canals are being stimulated while the head is not in motion. The direction of ocular movement is related to the semicircular canal that is being stimulated.

There are two key forms of nystagmus: pathological and physiological, with variations within each type. Nystagmus may be caused by congenital disorders, acquired or central nervous system disorders, toxicity, pharmaceutical drugs, alcohol, or rotational movement. Previously considered untreatable, in recent years several pharmaceutical drugs have been identified for treatment of nystagmus. Nystagmus is occasionally associated with vertigo.