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Horizontal Gaze Nystagmus
This test refers to an involuntary jerking occurring as the eyes gaze toward the side. In addition to being involuntary the person experiencing the nystagmus is unaware that the jerking is happening.
Many authorities state that this test is the most reliable field test. In administering this test, the officer has you follow the motion of a small stimulus with your eyes only. The stimulus may be the tip of a pen or pen light, an eraser on a pencil or your fingertip, whichever contrasts with the background.
When the HGN test is administered the officer is suppose to always begin with your left eye. Each eye is examined for three specific clues:
- As the eye moves from side to side, does it move smoothly or does it jerk noticeably?
- When the eye moves as far to the side as possible and is kept at that position for several seconds, does it jerk distinctly?
- As the eye moves toward the side, does it start to jerk prior to 45 degree angle?
As a person’s blood alcohol concentration increases we are told that it is more likely that these clues will appear.
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