Horizontal Gaze Nystagmus Test

Nystagmus is the medical term used to describe the involuntary jerking of the eyeballs. When someone is intoxicated by alcohol and/or certain drugs, this jerking becomes more pronounced. As such, the horizontal gaze nystagmus test is used by law enforcement agents to evaluate an individual’s nystagmus in order to determine if probable cause exists for a drunk-driving arrest.