Name a standardized field sobriety test used to assess impairment.

• A. Breathalyzer test.
• B. A visual acuity test.
• C. Horizontal Gaze Nystagmus (HGN).
• D. Blood pressure measurement.

Answer: (C)

Standardized field sobriety tests evaluate impairment through observable cues, and Horizontal Gaze Nystagmus is a key part of that set. This test relies on a natural eye movement phenomenon: when someone is impaired, nystagmus (involuntary eye jerking) becomes apparent as the eyes track a moving target. In practice, the officer has the person follow a smoothly moving object with their eyes while keeping the head still, watching for three clues in each eye: lack of smooth pursuit, distinct nystagmus at maximum deviation, and onset of nystagmus before 45 degrees of lateral gaze. The presence of multiple clues suggests impairment and can justify further testing or action. The other options aren’t field sobriety tests: a breathalyzer measures blood alcohol content from a breath sample, not a field test; a visual acuity test checks vision clarity, not impairment from substances; and blood pressure measurement assesses circulation, not impairment due to alcohol or drugs.