What does maximum deviation refer to in the context of HGN?

Maximum deviation, in the context of Horizontal Gaze Nystagmus (HGN), refers to the outward point where the eye cannot smoothly follow a stimulus. This phenomenon occurs when the eye is moved to the extreme lateral position, and it demonstrates a key indicator of potential impairment. When evaluating an individual's eye movements, the maximum deviation is noted when the eye exhibits a jerking or nystagmus motion at the farthest endpoint of gaze. This reaction can be attributed to neurological impairment or intoxication, making it significant in field sobriety tests.

The concept of maximum deviation helps law enforcement and trained professionals in determining the presence of alcohol or drug effects by observing these involuntary eye movements. The other options do not accurately capture this meaning—one describes an entirely different phenomenon, while others do not pertain to the critical characteristics assessed during the HGN evaluation. Understanding maximum deviation is essential for correctly interpreting the results of HGN tests and making informed decisions in situations involving suspected impairment.