Written by attorney Daniel F. Farnsworth

SFST Guide with clues


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.


  1. Remove glasses/ask if wearing contacts (note type of contacts)
  2. Position feet together and place hands at side
  3. Keep head still during test

    1. Follow stimulus with eyes only
  4. Position stimulus 12-15" from person’s face in front of the subject’s nose slightly above eye level

Preliminary Tests:

  1. Tests are separate and distinct from actual test
  2. Can not be done in conjunction or at same time as actual test

Equal Tracking:

  • Make two (2) complete passes starting with the left eye first
  • Move stimulus rapidly from subject’s center to far right, to the far left and back to center (approximately 2 seconds)
  • Both eyes should track stimulus equally

    • If eyes fail to track equally, discontinue test

Equal Pupil Size:

  • Both pupils should be of equal size



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.

  1. Two complete passes starting with left eye
  2. Move stimulus slowly to left at speed of about two seconds to bring eye completely to the side

    1. It should take TWO SECONDS from extreme left to center and two seconds from extreme right to center
  3. Each eye is checked twice

  4. NOTE: The eye should glide smoothly as the subject follows the stimulus like marble on a pane of glass.

    1. If the eye jerks as it moves side to side then the clue should be noted

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.

  1. Move stimulus out far enough to the side that there is little or no white visible in the subject’s eye-Start with Left eye
  2. Hold stimulus in this position for at least FOUR SECONDS
  3. Check for Distinct Nystagmus
  4. Check each eye twice

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

  1. Slowly move stimulus across the subject’s visual field, documenting where the nystagmus (eyes tick back) begins
  2. Start with left eye, move the stimulus (at least FOUR SECONDS) from center of subject’s head to the 45 degree angle (approximately the outside of the subject’s shoulder)
  3. Carefully observe the eye for jerking while the stimulus is moving
  4. If jerking observed, stop and verify that it continues
  5. Jerking should begin prior to 45 degrees
  6. Check each eye twice

Clues (maximum): 6


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):

  1. Can’t balance during instructions
  2. Starts too soon
  3. Stops while walking
  4. Doesn’t touch heel to toe
  5. Steps off the line
  6. Uses arms for balance
  7. Improper turn/loses balance on turn
  8. Wrong number of steps

NOTE: if subject can’t do test, record as if all 8 clues present


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):

  1. Sways while balancing
  2. Uses arms to balance
  3. Hops
  4. Puts foot down

NOTE: if suspect can’t do test at all, record as if all four clues were observed

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