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Understanding the Horizontal Gaze Nystagmus Test

Napa-County-DUI-Attorney--300x199After stopping someone on suspicion of DUI, law enforcement officers have three field sobriety tests that have been standardized by the National Highway Traffic Safety Administration: walk and turn, one-leg stand and horizontal gaze nystagmus. The first two are relatively easy to understand, but the horizontal gaze nystagmus test, or HGN test, is a little more nuanced. Your Napa County DUI lawyer will be interested to know if an HGN test was performed and whether it was performed correctly.

What is Nystagmus?

Nystagmus refers to the involuntary back-and-forth oscillation of the eyeball that happens when there is a disturbance of the inner-ear system or the oculomotion control of the eye. Everyone has at least a slight nystagmus, and an HGN is a type of jerk nystagmus that includes saccadic movement in the direction of the gaze. HGN is involuntary, and you’re not aware of it when it’s happening since it doesn’t affect the vision.

Understanding the HGN Test

As your Napa County DUI lawyer can tell you, the arresting officer will look for three signs while conducting an HGN test: the onset of nystagmus prior to 45 degrees, a lack of smooth pursuit and/or a distinct nystagmus at maximum deviation. Two passes are conducted, so there’s a possibility for six clues to be observed. A minimum of four are needed to determine that you have a BAC of 0.10 percent or higher.

Some conditions may interfere with the test, including headlights, traffic passing too closely and dust or wind. Fatigue nystagmus can occur if the eyes are kept at maximum deviation for 30 seconds or longer. Finally, certain medications, nicotine, caffeine and aspirin can all cause nystagmus.

Retain a Skilled Napa County DUI Attorney Now

Whether you were given an HGN test or not, it’s crucial to retain an experienced Napa County DUI lawyer. Call Blackie Burak at either 1-866-BLCKDUI or (925) 933-4500 today.

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About the Author

Professional & trustworthy DUI & Criminal Defense Lawyer Blackie Burak, Esq. defending your rights.