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Horizontal Gaze Nystagmus Testing DUI Cases

"Nystagmus" is an involuntary twitching of the eye. This twitching is what the officer was looking for when he/she told you at the roadside "I am going to check your eyes". In administering this field sobriety test, the officer was looking for three things:

  • Lack of smooth pursuit
  • Distinct Nystagmus at maximum deviation
  • Onset of Nystagmus prior to 45 degrees
Test Administration

If the test had been appropriately administered, the officer would have begun by asking you to stand with your feet together, and arms at your side. You should then have been instructed to "follow the stimulus (usually the officer's finger, a pen, or a flashlight) with your eyes only, keeping your head still". Before beginning the test, the officer should have confirmed that you understood the instructions by directly asking you "Do you understand"? The officer should also have asked you if you were wearing contact lenses.

The officer should have then checked your eyes for "equal tracking" and also should have confirmed that you had equal pupil size. These determinations require one full pass (a full pass begins at the nose, and then continues first the driver's right, then back to center, to the driver's left, then back to center again).

The test should have continued with the officer checking both of your eyes for "lack of smooth pursuit" (The officer is looking for the involuntary jerking as your eyes move from side to side). This determination requires two full passes, and each pass should have taken a minimum of four seconds.

Other Factors an Officer is Looking For

In the next part of the test, the officer is looking for "Nystagmus at maximum deviation". (Maximum deviation occurs when the eye is brought all the way out toward the shoulder, and no white is visible at the outside of the eye). To perform this correctly, the officer should again have made two full passes, and should have held your eye at maximum deviation for a minimum of four full seconds.

Next, the officer should have checked for onset of Nystagmus prior to 45 degrees. Here the officer should have brought your eyes out from center very slowly and should have noted the angle of onset. Once the officer saw the angle of onset (if indeed the officer did see Nystagmus), then the officer should have stopped to verify its onset and occurrence. Again, this determination would have required two full passes. Finally, the officer should have checked for vertical Nystagmus. This should have been done by moving your eyes vertically once, and should have taken at least four seconds.

Benefit of an Attorney

Having evaluated hundreds of these cases it is evident that officers almost never administer this test properly. What is most unsettling is that administering this test incorrectly can actually cause the Nystagmus that the officer will later use against you to prove you were intoxicated!

The two things that almost every officer mistakenly does when administering this test is to move the stimulus too fast and to complete the test with too few passes. Another frequent mistake is to have the driver facing toward the patrol vehicle. The flashing lights from the patrol vehicle can also cause involuntary twitching.

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