Nystagmus Test

Posted on January 29, 2015

Nystagmus Test

Before you were arrested for DUI, you may have been requested to take a standardized field sobriety test. Your DUI attorney Redwood City representation can explain that there are typically three standardized tests approved by the National Highway Traffic Safety Administration. These tests include the one-leg stand, walk-and-turn test and the horizontal gaze nystagmus.


The last test refers to the rhythmic back and forth movement of a person’s eyeball that occurs after the inner ear system is disturbed. Everyone has some oscillation of the eyes. Eye movements are classified as either pendular movements or jerk movements. The HGN tests the jerk movement that is made when a person’s gaze is directed at an object. Because HGN is involuntary, a person who exhibits this motion is unable to control it. Additionally, this movement does not usually affect the person’s vision, so he or she may not even be aware of it.

Impairment Clues

There are several clues that DUI lawyers Redwood City CA can explain. These include a lack of smooth pursuit, a distinct HGN at maximum deviation, and an onset of this movement before 45 degrees.

Possible Errors

Some conditions may interfere with a nystagmus test. These conditions include wind irritants, visual distractions, variations in light and other distractions. Additionally, unimpaired individuals may also exhibit nystagmus, such as individuals who are affected by fatigue. Prescription medicines and over-the-counter medicines may also be responsible for this movement.

Further Legal Assistance

If you would like to learn more about the nystagmus test and how to counter other kinds of roadside test results, contact Silveira Law by calling (415) 795-3890.