Neurology. An involuntary, rapid, rhythmic movement of the eyeball, which may be horizontal, vertical, rotatory or mixed, i.e., of two varieties. Origin: Gr. Nystagmos = drowsiness, from nystazein = to nod This entry appears with permission from the Dictionary of Cell and Molecular Biology. Nystagmus n|ÉŞ|ˈ|s|t|æ|ɡ|m|É™|s is a condition of involuntary 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".Note however that "dancing eyes" is also a common term for [[Opsoclonus myoclonus syndrome.}.}. When 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 momentum. 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. (An OSH glossary used in safety and health at work which is, adopted by ILO {102}.. The term definition has been obtained from the secondary source