What is Horizontal Gaze Nystagmus defined as?

Horizontal Gaze Nystagmus is defined as the involuntary jerking of the eyes that occurs when a person gazes to the side. This physiological phenomenon can be indicative of impairment, particularly in the context of alcohol consumption. When a person's eyes are moved horizontally, the nystagmus becomes more pronounced, especially at higher levels of intoxication. This characteristic jerking motion is typically measured during field sobriety tests to assess potential impairment due to substances like alcohol.

Understanding Horizontal Gaze Nystagmus is crucial for law enforcement training, as it serves as one of the indicators in determining whether an individual may be under the influence. It is not related to blurred vision, rapid blinking, or focus issues, which are expressions of different ocular or neurological conditions. Instead, it specifically involves the control of eye movements in relation to gaze direction, making it a critical component in DUI investigations and assessments.