HGN Test Flashcards

During the HGN test instructions, the officer tells the subject: 'Keep your head still and follow the stimulus with your eyes only.' What is the primary reason for this instruction?

Answer: To isolate eye movement so nystagmus can be accurately observed

Keeping the head still ensures that only the eyes are moving, allowing the officer to accurately observe nystagmus without interference from head movement.

Which Central Nervous System (CNS) depressants other than alcohol are known to produce HGN?

Answer: Barbiturates, benzodiazepines, and some inhalants

CNS depressants including barbiturates, benzodiazepines, and inhalants can produce nystagmus similar to that caused by alcohol.

What is the correct sequence of HGN clue checks as prescribed by NHTSA?

Answer: Smooth Pursuit, Maximum Deviation, Onset before 45°

NHTSA prescribes checking Lack of Smooth Pursuit first, then Distinct Nystagmus at Maximum Deviation, then Onset Prior to 45 Degrees.

An officer estimates that nystagmus onset occurs at exactly 45 degrees. Should this be scored as a clue?

Answer: No, because the clue requires onset PRIOR TO 45 degrees

The clue is 'Onset Prior to 45 Degrees' — onset exactly at 45 degrees does not meet the standard and should not be scored as a clue.

Why is it important to check for equal pupil size before administering the HGN test?

Answer: Unequal pupils (anisocoria) may indicate a medical condition that could affect test validity

Anisocoria can indicate a neurological condition that may produce nystagmus independent of alcohol, which the officer must note and consider.

How many passes does the officer make for the Lack of Smooth Pursuit check (both eyes combined)?

Answer: Two complete passes (left to right, then right to left)

NHTSA requires two complete passes — moving the stimulus from center to one side and back, repeated twice — so the officer checks smooth pursuit thoroughly in both eyes.

A defense attorney argues that bright flashing lights from police vehicles behind the subject could have caused the observed nystagmus. Which SFST best practice mitigates this concern?

Answer: Position the subject so that flashing lights are not directly in their line of sight during testing

Officers should position subjects away from flashing lights, traffic, and other visual distractions to ensure environmental factors do not influence the HGN test.