How Gaze Nystagmus Tests

Many drivers after being stopped by police are surprised when police examine and test the driver’s eyes. What are police doing? They are performing the horizontal gaze nystagmus test. This test, like others administered by police, has a scientific aura of invincibility. What can you do to refute its results? Please call The Law Offices of Mark Blair immediately so he can explain the shortcomings and flaws of nystagmus.
• San Jose (408) 295-4343 • Oakland (510) 845-4343
• San Mateo (650) 344-4343 • Walnut Creek (925) 935-4343
• San Francisco (415) 664-4343 • Napa (707) 252-4343


The horizontal gaze nystagmus is one of the three standardized field sobriety tests recognized by the National Highway Traffic Safety Administration. It consists of the driver following with his or her eyes a horizontally moving object, typically a pen. The officer then measures the angle at which the driver’s eye begins a rapid jerking. The sooner the jerking begins, the more intoxicated the person supposedly is.

However, the test procedure is suspect, and the admission of its results should be contested. One reason is that its major proponent, the National Highway Traffic Safety Administration, issued the results of a study that concluded that officers at sobriety check points misidentified 15% of sober drivers as being “under the influence” as a result of using this test.

The test itself may be applied one of three ways. To measure the movement of the eyes, the officer may (1) determine the angel of onset of nystagmus, and/or (2) notice whether the jerking becomes more pronounced when the eye moves to “the lateral extreme” (outside the periphery of the eye); and/or (3) to notice the failure of the eye’s “smooth pursuit” of the moving object.

The officer administers the test by having the driver keep his or head straight ahead and follow the object with his or her eyes. The officer then takes a pen, holds it 12 to 15 inches directly in front of the driver above the eyes, and moves it slowly in a quarter of a circle from the front of the face to a point perpendicular to where the officer began. Once the officer detects the jerking, the officer holds the pen at that point and should continue to observe jerking as long as the person looks at the pen. The officer then performs the same test on the other eye.

The sooner the jerking (the “earlier the onset of nystagmus”), or so goes the theory, the more intoxicated the driver. Studies by the National Highway Traffic Safety Administration conclude that a 40 degree angle onset of nystagmus meant that the person had a blood level alcohol of .10%.
The many flaws with gaze nystagmus include:

Improper administration of one or more steps of the test

Example:  unless the officer stops the movement of the pen when the eye jerking begins, the initial jerking of the eyes can be a false sign of nystagmus

Improper number of clues considered

The National Highway Traffic Safety Administration requires that at least four of possible six clues be present for the officer to conclude that the driver’s blood level alcohol was .10% or higher.
It would be an error to permit such a conclusion with less than four being present.
The six clues are

  • lack of smooth pursuit in the left eye
  • lack of smooth pursuit in the right eye
  • distinct nystagmus at maximum deviation (left eye)
  • distinct nystagmus at maximum deviation (right eye)
  • angle of onset prior to 45 degrees (left eye)
  • angle of onset prior to 45 degrees (right eye)


Time is of the essence. Your driving privileges and liberty are priceless, so you must act quickly. Please call The Law Offices of Mark Blair immediately because he can help!

DISCLAIMER: The results of any person’s DUI case described on this web site and/or in the Bay Area DUI Law newsletter depend on factual and legal circumstances that are unique to a specific person. Information provided by this web site and/or the Bay Area DUI Law newsletter does NOT constitute a guarantee, warranty or prediction regarding the outcome of your legal matter. Any reference to laws, procedures, punishment or license consequences at court or the DMV in this web site and/or Bay Area DUI Law newsletter is NOT intended to be complete description of what can and will happen in any or every DUI case but instead is a simplified summary to facilitate the reader’s understanding of general issues involving DUI law. The law is in constant change; penalties and consequences change; as such, the reader should not and cannot rely upon anything mentioned in this web site and/or Bay Area DUI Law newsletter. The reader is strongly advised to seek competent legal counsel to ascertain the law, penalties and consequences that apply to his/her unique circumstances.