The Horizontal Gaze Nystagmus Test is a sobriety tests given by the police to a suspected drunk driver to determine whethe there is probable cause to arrest him or her. This is done when an officer holds his finger, pen, or other object 12 to 15 inches in front of your face and then moves it slowly towards your ear, while you follow the object just with your eyes. While doing this, he looks for three things:
- An inability to follow the movement smoothly with your eyes
- An inability to retain focus on the object and the jerking of the eyeball as it moves to the extreme range of peripheral vision
- The onset of "jerking" of the eyeball before a 45 degree angle has been reached
A point is assessed for each of these characteristics for each eye for a maximum of six (6) points. A score of four or more points establishes a likelihood that your blood alcohol concentration (BAC) is over 0.10%. This test is often performed with others, such as a One Leg Stand (OLS) Test and a Walk and Turn (WAT) test to establish probable cause to arrest you for DUI.
In New Jersey, failing this test can ONLY be used to establish probable cause to arrest for drunk driving, and not actual impairment.