HGN Test Flashcards

What is the approximate BAC at which Onset of Nystagmus Prior to 45 Degrees typically begins to appear?

Answer: 0.04–0.06

Research suggests that onset of nystagmus prior to 45 degrees typically appears around 0.04–0.06 BAC, making it an early and sensitive indicator.

Which of the following describes a condition that may cause resting nystagmus (nystagmus with eyes looking straight ahead)?

Answer: Certain neurological disorders or extremely high BAC

Resting nystagmus, present when the eyes look straight ahead, can indicate a neurological condition or very high BAC and should be noted before administering the standard HGN test.

During HGN testing on a nighttime traffic stop, the officer uses a penlight. What is the preferred position of the penlight tip relative to the subject?

Answer: Angled downward slightly so light does not blind the subject

The penlight tip should be angled slightly downward so that it illuminates the eye without shining directly into the pupil and blinding the subject.

An officer observes that one eye tracks smoothly while the other shows nystagmus. How should this be scored?

Answer: The eye showing nystagmus earns a clue; each eye is scored independently

Each eye is scored independently in the HGN test; nystagmus in one eye earns a clue for that eye even if the other eye tracks smoothly.

What does the NHTSA SFST student manual recommend if a subject refuses to follow the stimulus with their eyes during the HGN test?

Answer: Note the refusal in the report and move on to the next SFST

If a subject refuses to cooperate with the HGN test, the officer documents the refusal and proceeds to the remaining SFSTs or makes an arrest decision based on all available evidence.

Which statement about the relationship between HGN and cannabis (marijuana) impairment is accurate?

Answer: Cannabis does not reliably cause the standard horizontal gaze nystagmus clues

Research has not established that cannabis reliably produces horizontal gaze nystagmus; HGN is primarily associated with alcohol and CNS depressants.

What is the significance of the number '4' in the HGN scoring system?

Answer: Four or more clues out of six indicate a high probability of BAC at or above 0.08

NHTSA research established that scoring four or more of the six possible HGN clues correlates with a BAC of 0.08 or above with approximately 88% accuracy.