During a DUI investigation, the investigating officer may initiate several field sobriety tests (FST). One test that may be administered is the Horizontal Gaze Nystagmus Test(HGN).
The term “nystagmus” refers to the involuntary jerking of the eye. This involuntary jerking can be observed when the eye oscillates to the side. The angle at which the eye can rotate without jerking decreases with intoxication.
In administering the HGN, the officer will instruct the suspect to keep his head still while following a pen or a small light with his eyes. The officer will then move the pen or light to the side of the suspects face and evaluate the angle at which the nystagmus occurs in the suspect’s eyes.
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