The Horizontal Gaze Nystagmus (HGN) test, a component of the Standardized Field Sobriety Test (SFST) battery, is administered by law enforcement officers to assess potential alcohol or drug impairment. The duration of this specific evaluation is typically brief, generally requiring only a few minutes to complete. The examination involves observing a subject’s eye movements as they follow a moving stimulus, such as a pen or fingertip, from side to side.
The value of this assessment lies in its ability to provide objective indicators of impairment. Nystagmus, an involuntary jerking of the eyes, can be exacerbated or become more pronounced under the influence of certain substances. The HGN test is quick to administer and provides immediate, observable data, assisting officers in determining if further investigation, such as a breathalyzer test, is warranted. Its historical context is rooted in clinical neurology, adapting neurological examination techniques for roadside sobriety assessments.