The horizontal gaze nystagmus test is a common field sobriety test used to determine probable cause for a DUI arrest. However, the test is not always accurate.

About the Horizontal Gaze Nystagmus Test

The horizontal gaze nystagmus test is a type of field sobriety test used to measure nystagmus, which is the medical term for an involuntary jerking of the eyeballs. Nystagmus can occur for many reasons, but becomes more pronounced when someone is intoxicated.

To perform the test, an officer will hold a pen or other small object roughly 12 to 15 inches from your nose. He will slowly move it from one side to the other and ask you to follow the object with your eyes while keeping your head still.

The officer will look for jerking or bouncing eye movements while following the object, nystagmus that sets in before your eyes reach a 45-degree angle, or nystagmus at maximum deviation. Four or more observances of nystagmus are probable cause for a DUI arrest.

Reasons for a Failed Test

The horizontal gaze nystagmus test is only accurate in about 77% of cases. Reasons for a failed test could include:

  • You suffer from a natural nystagmus in your eyes.
  • You have the flu or an inner ear infection.
  • You've been diagnosed with muscular dystrophy, multiple sclerosis, epilepsy, or glaucoma. 
  • You were recently engaged in activities causing eyestrain or eye muscle fatigue.
  • You were taking certain pain medications, anticonvulsants, or antihistamines.
  • The officer moved the object too quickly.
  • The officer made the object come too close to your eyes.
  • You weren't allowed enough time to follow the object during the test.

If you were drinking several hours earlier, keep in mind that it's possible to have a nystagmus even after all alcohol clears from your blood.

Building an Aggressive Defense

Failing the horizontal gaze nystagmus test shouldn't be a reason for panic. An experienced DUI defense attorney can help you build an aggressive defense by investigating every option available to support your case. Call today to schedule a free, no-obligation initial case review with Virginia attorney T. Kevin Wilson.