The onset of nystagmus prior to which degree is considered a clue in HGN?

• A. 30 degrees
• B. 60 degrees
• C. 45 degrees
• D. 15 degrees

Answer: (C)

In Horizontal Gaze Nystagmus, a noticeable jerking of the eye as you look toward the side becomes a clue when it starts before the eye reaches 45 degrees of lateral gaze. That 45-degree point is the standard cutoff used in the SFST criteria to flag impairment; if nystagmus begins earlier than that, it suggests CNS impairment from alcohol or drugs. The other degrees don’t match the established threshold for this cue: 60 degrees is beyond the cutoff, and 15 or 30 degrees would be earlier than needed but the test uses 45 degrees as the defining limit.