How long should a subject's gaze be held at maximum deviation during the HGN test?

Holding a subject's gaze at maximum deviation for about four seconds during the Horizontal Gaze Nystagmus (HGN) test is critical for accurate assessment. This duration allows the officer to observe any nystagmus (involuntary eye movement) that may occur at the edges of the subject's visual field. A longer hold at maximum deviation increases the likelihood of detecting the presence of nystagmus, as it provides adequate time for the eye to respond to the position and stability required during the assessment. This ensures that the observation is not rushed, allowing for a more reliable determination of whether the subject may be impaired.