What is horizontal gaze nystagmus?

The horizontal gaze nystagmus test is a normal part of the standardized field sobriety test battery

If you’re stopped for suspected drunk driving, frequently law enforcement officers will require you to complete a battery of standardized field sobriety tests.  Those tests include the one-leg stand test, the walk and turn test, and horizontal gaze nystagmus, or HGN.

Horizontal gaze nystagmus is the most difficult test for law enforcement officers to administer.  It’s frequently incorrectly interpreted and incorrectly administered.  Additionally, unfortunately it’s frequently  relied on when determining whether the officer will arrest the subject for operating while intoxicated.  Obviously these factors are all problematic.  The dedicated drunk driving attorneys at Van Severen Law Office understand the test and how to challenge it.

Finally, upon an arrest for drunk driving, contact our firm immediately.  Our drunk driving defense attorneys regularly defend individuals facing drunk driving charges.  Whether it’s your first offense, your tenth, or anywhere in between, we can help.  Certainly call us at (414) 270-0202 at your earliest convenience.

What is horizontal gaze nystagmus?

Nystagmus is a commonly-observed physiological phenomenon involving rapid involuntary oscillation of the eyes.  Gaze nystagmus, or “jerk nystagmus” is characterized by a slow drift of the eyeball, “usually away from the direction of the gaze, followed by a quick jerk or recovery in the direction of the gaze.”  The Merck Manual of Diagnosis and Therapy 1980 (14th ed. 1982).  Frequently law enforcement officers refer to “jerking of the eyes.”  This is incorrect and frequently leads to confusion.  Instead, nystagmus is a slow drift of the eyeball towards the nose.  A saccade is a quick corrective movement of the eyeball to the lateral position.  These are two distinct principles – but nystagmus is what law enforcement officers are looking for in the HGN test.  Saccade, or the jerky return, is an associated phenomenon.

Police officers wait to conduct a drunk driving test
Horizontal gaze nystagmus testing usually occurs after an OWI stop. Contact us at (414) 270-0202 for help.

The impact of alcohol on HGN

Research shows that acute alcohol intoxication causes gross motor defects such as sluggish physical response, poor coordination, emotional instability, and behavior changes.  Gregory W. Good & Arol R. Ausburger, Use of Horizontal Gaze Nystagmus as a Part of Roadside Sobriety Testing, Am. J. Optometry & Physiological Optics 467 (1986).  Further studies show that alcohol intoxication also impacts eye movement.  Id.  Specifically, alcohol hinders the brain’s ability to control eye muscles.  The National Highway Traffic Safety Administration relied on this connection when they devised the three standardized field sobriety tests we see administered today.

Importantly, congenital eye disease present from birth sometimes causes nystagmus.  Similarly, a head injury, disorders of the inner ear, and certain vitamin deficiencies also cause nystagmus.  If these issues cause nystagmus, rather than intoxication, you may be in the position to challenge your arrest.  Obviously there are other determinations your drunk driving defense attorney will make when evaluating these decisions.  How poorly did the other SFSTs go?  Did you admit to intoxication?  Certainly these are just two of a number or relevant questions to this decision.

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How do law enforcement personnel administer the horizontal gaze nystagmus test?

The NHTSA requires that the law enforcement administer the HGN test in a specific manner.  They break the test down into nine parts:

  • Firstly, check for eyeglasses.  The officer instructs a drive who wears glasses to remove them.  Sometimes law enforcement will even ask that individuals with contacts also remove them.  Eyeglasses may impede the subject’s peripheral vision and may impede the officer’s ability to observe the eye.  Law enforcement use a stimulus during the test, but the driver’s ability to see that stimulus with perfect clarity is not required.
  • Secondly, provide verbal instructions for the test.  The officers instructs the subject to put his feet together with his hands at his side, keep his head still, look at the stimulus, follow the movement of the stimulus with the eyes only, and continue looking at the stimulus until the test is complete.  Law enforcement personnel look for the defendant to sway, wobble, or try to keep balance during the instruction phase.
  • Thirdly, the officer positions the stimulus.  The officer places the stimulus 12-15 inches in front of the subject’s nose and slightly above eye level.  At this point the officer checks whether the subject displays resting nystagmus.

The observation phase

  • Next up, the law enforcement officer checks for equal pupil size and resting nystagmus.  If the officer observes resting nystagmus, he continues to check for other signs of impairment with the rest of the test.
  • Equal tracking.  At this point the officer moves the stimulus from center to far right, to far left, back to center.  There should be a clear, distinguishable break between the check for equal tracking and lack of smooth pursuit (the next step).
  • Sixth, the officer looks for lack of smooth pursuit.  The law enforcement moves the stimulus, using the same right, left, back to center movement for each eye.  The officer checks to see if the eye jerks while moving, indicating that there is not smooth pursuit.  This is one clue of intoxication.
  • Next, the officer checks for distinct and sustains nystagmus at maximum deviation.  The officer looks for distinct, sustained jerkiness, which is one clue.  He checks each eye separately.
  • Eighth,  the officer looks for onset of nystagmus prior to 45 degrees.  He checks each eye separately.  If he observes jerking prior to 45 degrees, that’s one clue.
  • Finally, the officer checks for vertical nystagmus in each eye.  During the VGN test, the officer looks for jerking as the eye moves up and at maximum elevation.  The stimulus should be 12-15 inches in front of the subject’s nose.

Contact Van Severen Law Office for top drunk driving defense

Hiring a top drunk driving defense lawyer is certainly crucial to the success of your case.  Whether you’re charged with a misdemeanor OWI or a felony OWI, we can help.  Our criminal defense attorneys regularly challenge illegal police conduct by filing pre-trial motions.  Those motions certainly help in cases that involve police officers incorrectly applying standardized field sobriety tests, like this one.

Finally, we understand that drunk driving incidents frequently occur in the middle of the night.  And they occur on the weekends.  For that reason, we are available 24/7 at (414) 270-0202. Contact us.  We’ll set up an initial consultation.  And then we’ll start fighting your case.

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