Virginia DUI/DWI Horizontal Gaze Nystagmus Test
Police officers commonly use what are called field sobriety tests in order to determine if there is sufficient evidence of intoxication to make a lawful arrest. In the 1970s, the National Highway Traffic Safety Administration (NHTSA) developed three (3) standardized field sobriety tests to assist police officers in determining if a driver is under the influence of alcohol or other intoxicants. The Horizontal Gaze Nystagmus Test is one of the field sobriety tests that is standardized by the NHTSA.
Performing The Horizontal Gaze Nystagmus Test
The Horizontal Gaze Nystagmus (HGN) Test measures the involuntary jerking of your eye. Nystagmus—or the involuntary jerking of your eyes when they move from side to side—occurs naturally, but it becomes more pronounced when you are intoxicated. To perform the test, the police officer will instruct you to follow the movement of an object such as a pen or flashlight with your eyes while keeping your head still. While the police officer moves the pen from side to side in a horizontal motion, he will closely watch your eyes.
If you are impaired by alcohol or other intoxicants, you will likely be unable to smoothly track an object from side to side with your eyes. Additionally, the involuntary jerking of your eyes will be exaggerated and occur before your eyes are fully extended to the periphery. As the police officer watches your eyes, he will be looking for a total of six signs of impairment. If you exhibit four or more of the signs, you will be arrested for DUI/DWI.
Faults In The Test's Effectiveness
However, exaggerated nystagmus is not only caused by alcohol or drug impairment. Physical conditions such as poor eyesight and neurological problems can cause you to fail the HGN test. Consequently, the HGN test has been criticized as unreliable even though it is supported by scientific evidence. The HGN Test is also criticized because the results are subjective and can be easily influenced by a police officer’s predetermined opinion of your impairment. Additionally, the HGN test is not always administered properly.