For Vertical Gaze Nystagmus to be recorded, how long should it be definite, distinct and sustained for?

To accurately assess Vertical Gaze Nystagmus (VGN), it is crucial that the nystagmus is observed as definite, distinct, and sustained for a minimum duration of 4 seconds. This duration allows the evaluator to clearly identify the involuntary eye movement that characterizes VGN, which is often associated with high levels of certain substances, particularly alcohol. By ensuring that the observation period meets this 4-second mark, the officer can confidently determine if the nystagmus is a reliable indicator of impairment.

In contrast, durations shorter than 4 seconds may not provide enough time to distinguish between variations in eye movement that might not be indicative of impairment. It's important for officers to adhere to this standard to maintain the integrity of the assessment process.