What does distinct a sustained nystagmus at maximum deviation indicate?

The correct answer indicates that distinct sustained nystagmus at maximum deviation shows that the gaze of the eye is held at maximum deviation for four seconds. This is a key indicator in the field of DUI assessments, particularly during the Horizontal Gaze Nystagmus (HGN) test. When an individual is under the influence of certain substances, their ability to control eye movements may be impaired, resulting in nystagmus, which is an involuntary eye movement.

Sustained nystagmus occurs when the eyes fail to smoothly track an object and hold at the extreme left or right gaze position for a prolonged duration, specifically four seconds or more. This behavior provides valuable insight into the level of impairment of the individual, as it may signal intoxication or the influence of drugs affecting the nervous system.

The other choices do not reflect an accurate understanding of the behavior exhibited in this context. For instance, being able to track smoothly would indicate normal function, while easily focusing on an object suggests no impairment, and no deviation in eye movement would indicate a lack of nystagmus altogether. Recognizing these distinctive signs is crucial for law enforcement in assessing a driver's impairment during a traffic stop.