Horizontal Gaze Nystagmus (HGN)

Horizontal Gaze Nystagmus (HGN) is an involuntary movement of the eyes that occurs when a person looks to the side. It is characterized by a rhythmic, back-and-forth shaking of the eyes, which can be more pronounced at certain angles. HGN is often used as a field sobriety test because alcohol and some drugs affect the nervous system, making this eye movement more noticeable. The presence of HGN can indicate impairment, but it is not solely definitive and is usually considered alongside other tests and observations in assessing sobriety.