What is the first clue observed in the HGN test?

In the context of the Horizontal Gaze Nystagmus (HGN) test, the first clue typically observed is the failure to track smoothly. This phenomenon occurs when the eyes are unable to follow a moving stimulus, such as the tip of a pen or a finger, in a seamless motion. Instead, the eyes exhibit jerking or jerky movements, indicating a lack of smooth pursuit. This failure can suggest impairment, often associated with intoxication or certain neurological conditions.

Understanding this initial indication is crucial when conducting the HGN test, as it sets the stage for further evaluation and analysis of the subject's eye movements. Recognizing this first clue allows the examiner to continue assessing the other components of the HGN test, such as the onset of nystagmus prior to 45 degrees and maximum deviation. These subsequent indicators provide additional evidence of potential impairment, which helps in forming a comprehensive assessment.