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Why the horizontal gaze nystagmus test is problematic

On Behalf of | Apr 22, 2022 | Criminal Defense |

When an officer pulls you over because he suspects that you are drunk driving, he may ask you to perform several field sobriety tests. In addition to the one-leg stand test and the walk-and-turn test, he will ask you to perform a horizontal gaze nystagmus test.

Unfortunately, field sobriety tests are not necessarily accurate. The horizontal gaze nystagmus test (HGN), in particular, is unreliable because there are several other reasons aside from intoxication that can cause your gaze may be unsteady or unfocused. 

What is the horizontal gaze nystagmus test?

Horizontal gaze nystagmus is an involuntary jerking or twitching of the eye when you shift your gaze from side to side. Alcohol consumption can exaggerate this condition, which is why it is used in field sobriety tests. 

Unfortunately, the HGN test is unreliable at best because there are other reasons that could cause the same eye-jerking results including:

  • Inner ear fluid movement
  • Antidepressants
  • Seizure medication
  • Head injury
  • Contact lenses
  • Caffeine
  • Drowsiness
  • Dry or irritated eyes
  • Smoking
  • Stress

In addition to these conditions, the officer performing the test may make mistakes. The test must be performed at a 45-degree angle from 12-15 inches away. His eyes need to be parallel to your eyes. If any of these factors are not met, the test results are invalid. The NHTSA warns that nearly 95% of the HGN tests given have inaccurate results. This is why these tests are often inadmissible in court.

Should you be pulled over by an officer who administers these tests and declares you are operating while impaired (OWI), you will be arrested. Experienced legal guidance is the key to getting through this situation.