What does a strong response to HGN usually indicate?

A strong response to Horizontal Gaze Nystagmus (HGN) typically indicates severe levels of intoxication. HGN is a field sobriety test used primarily to assess a person's impairment due to alcohol consumption. When a person is intoxicated, their eyes exhibit certain involuntary movements, such as nystagmus, when they are asked to follow a target horizontally. A pronounced nystagmus response at specific angles—usually at 45 degrees or sooner—suggests a higher blood alcohol concentration (BAC) which correlates with significant impairment. This response indicates that the individual may have compromised coordination and judgment, making it unsafe for them to operate a vehicle. Thus, the correct understanding is that a strong response is a clear sign of severe intoxication and suggests that the person is likely unable to drive safely.