arizona misdemeanor

The Horizontal Gaze Nystagmus Test

(Last Updated On: November 5, 2018)

What is the Horizontal Gaze Test?

The horizontal gaze nystagmus test is one of the three standardized field sobriety tests used by the National Highway Traffic and Safety Administration to identify possible drunk drivers. This test has been studied to be the most accurate of the three, with a 77 percent accuracy rating in detecting blood alcohol content (BAC) of .10 or higher.


What is Nystagmus mean?

The term “nystagmus” is defined as involuntary jerking or bouncing of the eyeball, which occurs when there is an irregularity in the inner ear system or a problem affecting the oculomotor control of the eye.

The test is designed to identify a lateral or horizontal jerking movement when a person looks toward the side, at an angle greater than 45 degrees.


How Accurate is HGN Testing?

This test is fairly new to field sobriety tests, but is determined to be fairly accurate when administered properly. When a person has a high BAC, their eye will twitch when a light is held near the eye and looking at an angle less than 45 degrees.

The police officer administering the test must have had HGN training. It is the only test out of the three main field sobriety tests to have scientific support. In states like Arizona that admit HGN test results into evidence, it may be used as the basis for probable cause for a DUI arrest.

Unlike BAC level, you do not just fail or pass a HGN test for high BAC. It is used as a general indicator of possible impairment.

There are three clues for each eye that the officer is looking for: do your eyes move smoothly or jerk noticeable? Do your eyes jerk when you move them to the side as far as possible? And does your eye start to jerk before it has moved through a 45-degree angle?

In order for the test to be administered successfully, the subject’s eyes must be seen clearly. The subject should remove eyeglasses so the officer can better observe eye movement, although glasses and contact lenses do not affect the HGN test results.

The test should be administered in a well-lit area or by use of a flashlight to illuminate the subject’s face. If the subject is facing blinking lights of a police cruiser or passing vehicles, the test may be dismissed.


Can this Test be Challenged in Court?

While this test has been proven to be accurate, many lawyers still try and challenge it’s credibility in court. One of the biggest reasons for this is that the officers who administer HGN tests are not medically trained, and as a result their ability to assess the angle at which nystagmus begins is at risk of being skewed.

To build a stronger case against a diver suspected of a DUI, officers will use the test in conjunction with other field tests, including breathalyzer tests or urine or blood tests.

If you are suspected of a DUI, you should seek legal representation as soon as possible.

The Tucson DUI lawyers at Thrush Law Group will concentrate their efforts on defending you with a diligent approach that offers the best chance of dismissal or acquittal.

Posted in Arizona DUI Law.


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