Horizontal Gaze Nystagmus

What does Horizontal Gaze Nystagmus mean?

Horizontal gaze nystagmus is the involuntary rhythmic eye movement from side to side which can be exacerbated by consuming large quantities of alcohol. The National Highway Traffic Safety Administration (NHTSA) has three standardized tests to determine whether a driver is intoxicated. One of these tests is the horizontal gaze nystagmus test. The underlying premise of the HGN test was that it would allow for increased detection of intoxicated driving and more impaired driving arrests, higher conviction rates and ultimately lower incidents of DUI.

To administer the HGN test the officer can use a flashlight to illuminate the driver's face. The officer must notify the driver they are testing the driver's eyes. Then the driver is asked to track an object with their eyes, generally the tip of a pin light. The officer places the object approximately twelve to fifteen inches from the subject's face and slightly higher than eye level. The officer instructs the driver to follow the object with their eyes only. The officer is looking for lack of smooth pursuit, distinct nystagmus at maximum deviation, and whether the angle of the onset of nystagmus is prior to forty-five degrees.

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