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Definition - What does Gaze Nystagmus mean?
Gaze nystagmus is a rapid eye movement, made apparent when a person's eyes involuntarily shake when they look to the right or to the left. The eyes can also bounce or jerk when the person's eyes are fixed on a certain object or picture, as well. Many call this phenomenon "dancing eyes." Because alcohol has a slowing affect to human senses and body functions, during alcohol induced gaze nystagmus, the eyes twitch due to trying to "catch up" with the object they are following, or to try to focus on the fixated object. Officers often look for this trait in an individual who is suspected of being under the influence of alcohol while driving.
How to Identify Gaze Nystagmus
Gaze nystagmus is an easy thing to detect visually when examining a person, however, it is often overlooked. When it comes to drunk drivers, officers are trained to identify nystagmus in a number of ways. The test officers normally use to identify this is called a Horizontal Gaze Nystagmus Test, or HGN Test. During a traffic stop of a suspected drunk driver, an officer would ask the individual behind the wheel to step out of the vehicle. The subject's eyes must be seen clearly by the officer, should remove glasses, and should not be facing oncoming headlights. The officer would then turn on a penlight, and ask the driver to follow the light with their eyes, keeping their head straight forward. During the test, an officer attempts to identify three indicators:
- If the eyes move smoothly or jerk involuntarily
- If the eyes jerk when moved to the side as far as possible
- If the eye jerks before moving through a 45 degree angle
Because alcohol can affect a person's peripheral vision, a driver who exhibits gaze nystagmus will experience a twitching in the eye that is trying to focus on an object. According to the National Highway Traffic Safety Administration, HGN tests are:
- Very accurate if administered properly, and the officer has gone through HGN training
- Has scientific support in its effectiveness to identify Alcohol Gaze Nystagmus
- Administered by officers in many states, but not all states