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DUI defense attorney in Pierce County | Attorney South King County criminal attorney

About the Nystagmus Test

Three standardized field sobriety tests are commonly used in drunk driving cases, and a DUI defense attorney in Pierce County can advise you about them. The battery includes the walk and turn, the one-leg stand, and the horizontal gaze nystagmus test.

DUI defense attorney in Pierce County

What Is Nystagmus?

Nystagmus is a jerking motion of the eyes. More accurately, it is an oscillation of the eye caused by an inner ear disturbance or disruption of motor control of the eye.

The eyes oscillate normally, but only very slightly. A specific type of nystagmus, horizontal gaze nystagmus (HGN), is a type of repeated lateral movement of the eye to the side in the direction that the person is looking.

You cannot control HGN, and may not even know it is happening since vision is not greatly affected by the eye shift. According to the National Highway Traffic Safety Administration, HGN is strongly correlated to alcohol consumption. As a result, a test of the eye bounce is often used as a sobriety test.

Measurement Error

A DUI defense attorney in Pierce County will explain that many factors can interfere with the accuracy of the HGN test. These include wind or other eye irritants, or visual distractions such as lights from passing cars or police car strobes. In addition, the condition may be the result of fatigue rather than alcohol. The test itself can cause fatigue, as subjects try to hold eyes steady for extended periods. Prescription or over-the-counter medication may be contributing influences, and coffee or cigarettes may impact eye steadiness.

When administering the test, the officer looks for hints of impairment including 1) lack of smooth eye movement when following an object, 2) clear presence of nystagmus before the eyes are moved 45 degrees to the side, and 3) a bounce of the eyeballs when gazing fully to the side. The three observational measures add up to six scores, because the test is repeated. If the person shows HGN on any four of the six assessments, officers interpret this as an indicator of a blood alcohol level above 0.10 percent.

Contact Us

If you have been administered an HGN test or accused of DUI, contact an experienced DUI defense attorney in Pierce County by calling

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