Horizontal Gaze Nystagmus

HGN refers to an involuntary jerking of the eyes occurring as the eyes gaze toward the side. The theory behind the test is that nystagmus becomes readily noticeable when a person has a blood alcohol concentration of .08 or above, or is under the influence of a central nervous system depressant.

In administering the test the officer has the subject follow the motion of a stimulus with the eyes only. The stimulus may be the tip of a pen, penlight, eraser on a pencil or a fingertip. As the eyes move from side to side each eye is examined for three specific clues:

Administering the HGN is highly technical. Police frequently fail to properly administer it, which is supposed to be the most reliable of all the SFSTs.

You need an experienced DWI attorney to review and expose any errors made in its administration.

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