What does the onset of nystagmus before 45° indicate?

The onset of nystagmus before reaching a 45° angle is indicative of possible impairment. Nystagmus is an involuntary movement of the eyes, and in the context of DUI evaluations, its presence can suggest a level of impairment related to the consumption of alcohol or drugs. When an officer conducts a standardized field sobriety test, specifically the Horizontal Gaze Nystagmus (HGN) test, observing nystagmus at angles less than 45° is a significant signal. It suggests that the person may not be functioning normally or that their motor skills or cognitive processing may be affected by substances. Thus, detecting nystagmus before 45° is a key indicator that further evaluation is needed to assess the individual's level of impairment and their ability to safely operate a vehicle.