When checking for the Onset of Nystagmus Prior to 45 Degrees, how long should the stimulus be moved side to side?

In the context of assessing the onset of nystagmus prior to 45 degrees during the Horizontal Gaze Nystagmus (HGN) test, the correct duration for moving the stimulus side to side is indeed 4 seconds. This duration is crucial because it allows for a proper evaluation of the eye movements and the presence of nystagmus. When the stimulus is held for this time frame, it ensures that the examiner can clearly observe any involuntary jerking of the eyes—known as nystagmus—beginning before the 45-degree angle.

This systematic approach helps in obtaining reliable results, as any shorter duration may not provide enough time to see a definitive onset of nystagmus, potentially leading to inaccurate conclusions about the level of impairment. Moreover, holding the stimulus steady for 4 seconds is aligned with standardized protocols, which contribute to the validity and reliability of the sobriety test being administered.