Optokinetic nystagmus
In police work, testing for horizontal gaze nystagmus is one of a battery of field sobriety tests used by officers to determine whether a suspect is driving under the influence of alcohol. The test involves observation of the suspect's pupil as it follows a moving object, noting
lack of smooth pursuit,
distinct and sustained nystagmus at maximum deviation, and
the onset of nystagmus prior to 45 degrees.
The field sobriety test studies published by the National Highway Traffic Safety Administration have never been peer reviewed and attempts to duplicate the study results have been unsuccessful.[4]
The horizontal gaze nystagmus test has been highly criticized and major errors in the testing methodology and analysis found.[5][6] However, the validity of the horizontal gaze nystagmus test for use as a field sobriety test for persons with a blood alcohol level between 0.04-0.08 is supported by peer reviewed studies and has been found to be a more accurate indication of BAC than other standard field sobriety tests.[7]
Phenytoin, a common seizure medication, is also a cause of nystagmus.
http://en.wikipedia.org/wiki/Physiologic_nystagmus
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