What is Horizontal Gaze Nystagmus (HGN)?

Horizontal Gaze Nystagmus (HGN) refers to the involuntary jerking of the eyes as they move to the side. This phenomenon is frequently observed during the assessment of individuals suspected of driving under the influence. When a person is asked to follow an object (like a pen or a finger) with their eyes, HGN can occur, especially when the individual is under the influence of alcohol or certain drugs.

The presence of HGN can indicate a potential impairment, as the smoothness of eye movement typically decreases with certain intoxications. As such, law enforcement officers trained in the field of drug recognition often utilize this involuntary response as part of their evaluation process. Understanding HGN is crucial for recognizing signs of impairment effectively during roadside assessments.