How Horizontal Gaze Nystagmus (HGN) Works?
Since alcohol suppresses the nervous system, it is difficult to make eye movements that are smooth and accurate. For such reasons, police officers tend to look for exaggerated eye jerks to determine if there is alcohol in an individual’s system.
The police officer often tells the driver that they are going to check their eyes and asks them if they wear contact lenses or have medical issues that would affect results. Then they ask the driver to follow an object with their eyes (typically a pen) and place it twelve to fifteen inches away from their eyes. The police officer will use a flashlight to determine if there is sudden jerking of the eyes.
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Are Horizontal Gaze Nystagmus (HGN) Tests Reliable?
According to the National Highway Traffic Safety Administration (NHTSA), field sobriety tests show accurate blood-alcohol concentration (BAC) of .10 percent or higher 83 percent of the time. However, it is important to note that an HGN test is only a physical observation by the officer, which would highly depend on the officer’s level of training. Although it is found to have accurate results, the HGN test alone isn’t sufficient evidence to prove drunk driving.