HGN
Horizontal Gaze Nystagmus
The involuntary jerking of the eyes as they track an object to the side, and the first of the three standardized field sobriety tests. The officer moves a stimulus, usually a pen or a fingertip, and watches the eyes rather than the person.
Commonly heard as
“I'm going to check your eyes”
“Follow the tip of my pen with your eyes only”
Worth knowing
Administration procedure and the evidentiary treatment of the results both vary by jurisdiction, and HGN is the most frequently contested of the three tests.