/nəˈstagməs/
Noun
1. A condition of involuntary eye movement, acquired in infancy or later in life, that may result in reduced or limited vision. 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. (wikipedia.org)
2. Rapid involuntary eye movement, usually lateral. (wiktionary.org)
3. An involuntary, rapid, rhythmic movement of the eyeball, which may be horizontal, vertical, rotatory or mixed, i.e., of two varieties. (biology-online.org)
4. Involuntary movements of the eyeballs; its presence or absence is used to diagnose a variety of neurological and visual disorders. (wordnetweb.princeton.edu)
Word origin: Medical Latin, from Greek nystagmos “nodding, drowsiness,” from nystazein “to nod, be sleepy.”