Horizontal Gaze Nystagmus is a series of three tests for the smoothness and accuracy of eye movement control. The eye control becomes visibly disrupted to the examiner when a suspect is impaired by alcohol and/or drugs.
Keep head still during test
Position stimulus 12-15" from person’s face in front of the subject’s nose slightly above eye level
Both eyes should track stimulus equally
Equal Pupil Size:
THREE CLUES OF HORIZONTAL GAZE NYSTAGMUS
Lack of Smooth Pursuit-ability by the eyes to track and smoothly pursue a moving target. If disrupted, this is seen as the first sign or clue of impairment.
Move stimulus slowly to left at speed of about two seconds to bring eye completely to the side
Each eye is checked twice
NOTE: The eye should glide smoothly as the subject follows the stimulus like marble on a pane of glass.
Distinct Nystagmus at Maximum Deviation- ability by the eyes to hold steady while looking at a target moved as far to the left and right as possible. If disrupted, this is seen as the second sign or clue of impairment.
Onset of Nystagmus Prior to 45 Degrees- ability of eyes to hold steady when the eye is drawn toward the side slowly before it has moved through a forty-five degree angle
Clues (maximum): 6
WALK AND TURN TEST
This test requires the subject to stand in a heel-to-toe fashion with arms to the sides while a series of instructions are given. The subject must take nine heel-to-toe steps along an imaginary line, turn in a prescribed manner, and take nine heel-to-toe steps along the same line. All of this must be done while counting the steps out loud and keeping the arms at the sides. The subject should not stop walking until the test is completed. This is a divided attention test.
Clues (8 maximum):
NOTE: if subject can’t do test, record as if all 8 clues present
ONE LEG STAND
This test requires the subject to stand on one leg. The other leg is to be extended in front of the subject in a straight leg manner, with the foot held approximately six inches above and parallel to the ground. The subject is to stare at the elevated foot, and count aloud in the following manner: “one thousand one, one thousand two, one thousand three…" and so on until told to stop. The procedure will last for thirty seconds.
Clues (4 maximum):
NOTE: if suspect can’t do test at all, record as if all four clues were observed