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

For Vertical Gaze Nystagmus (VGN) to be properly recorded during a field sobriety test, the relevant observation must be definite, distinct, and sustained for at least 4 seconds. This duration is crucial because it allows the officer to accurately assess the presence of nystagmus, which is an involuntary eye movement that can indicate certain levels of intoxication, particularly from a central nervous system depressant like alcohol.

The 4-second timeframe ensures that the officer observes a clear and observable manifestation of nystagmus, which is necessary for it to be considered valid evidence in a sobriety assessment. Observing for less than this duration may lead to misinterpretation of the results, as it could lead to mistaken conclusions about a person's level of impairment.

While the other durations are presented as options, none provide the sufficient observation period needed to confidently conclude the presence of vertical gaze nystagmus.