Nystagmus is characterized by a jerky back and forth movement of the eyes. It can be genetic in origin, caused by damage in the womb, or caused by brain damage. Nystagmus can also be induced by
closing your eyes and spinning around in a chair. Police officers often check for nystagmus in drivers suspected of
driving under the influence. There is currently no cure for nystagmus, however operations that relax the
eye muscles have been tried with some success.
Biofeedback has also been used to help people with nystagmus to learn how to control it.
Normal people have minute lateral eye movements called saccades that are necessary for sight. These movements are more pronounced in people with nystagmus. Often, a person with nystagmus will attempt to compensate for these movements by unconsciously moving the head back and forth. This is often mistaken by observers as a "no" signal and can be detrimental in social situations.
As somebody who has genetically caused nystagmus, I prefer to think of nystagmus as "dancing eyes." More information may be found at http://www.nystagmus.org/