Field Sobriety Tests (Horizontal Gaze Nystagmus)

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According to the National Highway Traffic Safety Administration, Horizontal Gaze Nystagmus is the involuntary jerking of the eyes as they gaze to the side. The HGN test is commonly used by members of law enforcement in Fresno County, and throughout the state of California in conducting an investigation for driving under the influence. Many, if not all, officers claim that they observed a driver arrested on suspicion of driving under the influence have exhibited three scientifically validated clues of impairment in HGN. However, in most instances, the officer does not actually observe the clues or even know how to properly perform the test. The officer will simply claim that he or she observed the three scientifically validated clues and include them in their report.

Below are the clues of HGN and how the test should properly be performed. If you have been arrested on suspicion of driving under the influence, and the arresting officer failed to perform the HGN test correctly, it could impact whether the officer had probable cause to place you under arrest.

According to the NHTSA, there are three scientifically validated clues of impairment with HGN: (1) distinct, sustained nystagmus at maximum deviation; (2) lack of smooth pursuit; and (3) angle of onset.

To begin the test, the officer should have the driver remove all eyewear and stand straight with his or her feet together. (If the officer performed the test on you while sitting in your vehicle, the test was not administered properly.)

Lack of Smooth Pursuit

The officer should move the stimulus all the way to the subject’s left then move the stimulus smoothly all the way across the subject’s face to the right. The object MUST be moved steadily, at a speed that takes less than 2 seconds. The officer should check the left eye for lack of smooth pursuit. If the eye is observed to jerk while moving, that is a clue. Next, the officer should check the right eye.

Distinct, Sustained Systagmus at Maximum Deviation

The officer should position the stimulus (normally a pen or his or her finger) 12-15 inches in front of the subject’s nose. The stimulus should be moved to the subject’s left side until the eye has gone as far as possible. The officer should then hold the stimulus there for at least 4 seconds. If the eye jerks, it is a clue. The officer should repeat this step with the right eye.

Angle of Nystagmus Prior to 45 Degrees

The officer should move the stimulus across the subject’s face. Once jerking is observed, the officer should immediately stop moving the stimulus and hold it in that position. If the jerking is not continuing the officer should continue to check for the point of nystagmus. The officer should repeat the step with both eyes.

Based on research into HGN, there are 6 validated clues. Most officers will claim that they observed all six clues in each and every subject they arrest for driving under the influence. However, from experience it is clear that the officers performing the test are not performing the test properly. If the officer fails to properly perform the test, the clues that he or she observed are essentially meaningless.

If you have been arrested on suspicion of driving under the influence, and believe that the officer failed to properly perform the nystagmus test, or any of the many other field sobriety tests, feel free to contact our office and we will be glad to discuss your case with you.

In Fresno County, you should contact an experienced Fresno Criminal Defense Attorney who can assist you in your driving under the influence defense strategy.

If you have any questions regarding the services provided at the Law Office of Gregory W. Fox,
or would like to schedule your free initial consultation, please contact us today at (559) 222-5800. Hablamos español.