Driving Under the Influence

Question 1

What are normal eye movements?

Answer 1

Fixation, smoot pursuit, saccade, and convergence.

Question 2

What is fixation?

Answer 2

Fixation is the steady maintenance of eye position when there is no relative motion between the observer and the object, such as when a driver stopped at an
intersection looks at a traffic signal or a moving driver watches another vehicle that is traveling in the same
direction and at the same speed.

Question 3

What is smooth pursuit?

Answer 3

Smooth pursuit involves maintaining eye position on an object when
there is relative motion between the observer and the object, such as when a moving driver reads a stationary road sign or a driver stopped at an intersection watches a pedestrian crossing the street.

Question 4

What is saccades?

Answer 4

Saccades are rapid
scanning eye movements, such as when reading text like this or when a driver looks quickly from one part of
the road to another or to a mirror.

Question 5

What is convergence?

Answer 5

Convergence involves maintaining single vision on an object that changes in distance from the observer or when an observer
changes fixation between objects at different distances, such as when a driver looks from the road ahead to the dashboard or radio.

Question 6

What is nystagmus?

Answer 6

Nystagmus is the term used to describe an eye that is undergoing a repetitive, back-and-forth or “bouncing” movement. Nystagmus occurs when there is a disturbance of either the neurological control of the eye or the vestibular (inner ear) system.

Question 7

What is the medical rule out?

Answer 7

Resting nystagmus, equal tracking, and equal pupil size.

Question 8

What is equal tracking?

Answer 8

An observation of whether both of the subject’s eyes together can follow the object and that each eye has full range of motion, that is, is able to move all the way to either side. Checked by moving the object across the subject’s entire horizontal field of vision in a time of about 4 seconds in each direction twice.

Question 9

How many clues in HGN?

Answer 9

6 clues. 3 in each eye.

Question 10

What do clues of HGN indicate?

Answer 10

Impairment

Question 11

Why do we complete each test twice?

Answer 11

Each eye is checked twice for each clue, first to note the presence or absence of the clue, then to confirm the observation. If needed, the officer may individually check any clue for either eye additional times, the officer does not need to conduct the entire test again.

Question 12

What are the clues of HGN in order?

Answer 12

Lack of smooth pursuit, distinct and sustained nystagmus at maximum deviation, and onset of nystagmus prior to 45 degrees.

Question 13

Lack of smooth pursuit

Answer 13

• Stars from center to left ear (2 seconds)
• Across field of vision to right ear (4 seconds)
• Back to left ear (4 seconds)
• Back to right ear (4 seconds)
• Back to center (2 seconds)

Question 14

Distinct and sustained nystagmus at maximum deviation

Answer 14

• Starts from center to left, bringing eye as far as possible (4 second hold, time to get there irrelevant)
• ensures that movement of the object did not possibly cause endpoint nystagmus

Question 15

Onset nystagmus prior to 45 degrees

Answer 15

• 4 seconds to reach the edge of the subject’s left shoulder
• clue if the point or angle at which the eye begins to display nystagmus is before the
  object reaches 45 degrees from the center of the subject’s face

Question 16

Vertical gauze nystagmus

Answer 16

• from center to several inches above head
• 4 second hold at the top
• repeat
• positive if the subject exhibits a vertical jerk nystagmus; if nystagmus is horizontal or rotatory, while abnormal, or if there is no nystagmus, then the VGN test is negative
• When caused by intoxication, the presence of VGN is a good indicator of a
  high dose of alcohol, other CNS depressant drugs, inhalants, or dissociative
  anesthetics for that subject