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How does the horizontal gaze nystagmus field sobriety test work?

How does the horizontal gaze nystagmus field sobriety test work?

| May 4, 2021 | DUI/DWI |

Police officers have an array of tools and procedures to help them determine if a motorist is intoxicated. They may ask you to walk a straight line and turn around or stand on one leg for a time.

Another standard field sobriety test is the horizontal gaze nystagmus (HGN) test. Looking at these three words, you can deduce that gaze means looking at something. Horizontal essentially means sideways instead of up and down. Nystagmus refers to involuntary eye movements.

How does the HGN indicate intoxication?

According to the science behind the test, alcohol consumption increases involuntary eye movements without your awareness. As such, police officers are trained to identify pronounced nystagmus when conducting field sobriety tests.

Law enforcement officers look for three clues when performing an HGN test.

  1. Smooth pursuit. An officer asks you to hold your gaze on an object as it moves. If your eyes do not follow the item smoothly, it could be a sign of intoxication.
  2. Nystagmus at maximum deviation. Police officers ask you to look as far to one side as possible and hold your gaze for four seconds. If your eyes jerk or move distinctly, officers may believe you are drunk.
  3. Nystagmus before 45 degrees. The police want to see what your eyes do as you track a moving object to the side. If your eyes jerk before the item reaches 45 degrees from the center of your face, it could result in a drunk driving arrest.

From a defense perspective, there are numerous potential problems with the HGN test. For example, the test must be conducted in a well-lit area to be effective. The test must also conform to established standards created by the National Highway Traffic Safety Administration (NHTSA).

If you need an effective defense against drunk driving charges, an attorney can investigate how police officers conducted the field sobriety tests. If they uncover any problems with the test, it could help you fight the charges against you.