A Criminal Lawyer Pierce County Discusses the Horizontal Gaze Nystagmus Test

Monday, June 1st, 2015

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DUI police car at night Criminal Lawyer Pierce County Field sobriety tests are tools employed by law enforcement to gather evidence to establish probable cause for a DUI arrest. Despite the variety of different FSTs used, only three have gained “standardized” status as measured by the National Highway Traffic Safety Administration. One such standardized test is the HGN test.

What the HGN Test Measures

Nystagmus is an involuntary twitching or jerking of the eyes that occurs naturally. Most often, it occurs when a person’s head is held still, and the eyes attempt to look in a direction of about 45 degrees. The HGN test is designed to detect the difference in the eye movements that a sober person would exhibit in contrast to those of a person impaired by alcohol consumption.

Evidence of Impairment

Two passes of either a penlight or finger are made in front of the suspect’s face, and each eye is observed by the officer administering the test; thus, there are six potential test subjects. If the officer detects four signs of impairment, that is considered reflective of a blood alcohol level of .10 or higher. The signs of impairment are:

  • The eye cannot follow the object smoothly
  • The jerking of the eye is distinct at maximum deviation
  • The onset of the jerking is within 45 degrees of center

Understanding the Results of a HGN Test

An experienced criminal lawyer Pierce County understands there can be many reasons for test results. For instance, there are over 40 types of nystagmus, and only two involve alcohol consumption. Additionally, the officer must be sufficiently trained in administering any FST used, and the test must be properly administered. As an example, dust or wind can be an irritant in a person’s eyes that can skew the results, as can be visual distractions such as passing headlights. Finally, the ingestion of certain medicines can cause similar reactions as triggered by alcohol consumption.

Contact a Criminal Lawyer Pierce County for Legal Advice

An arrest on a DUI charge does not necessarily mean a conviction. Explore your options. Call Greene & Lloyd, PLLC, a criminal lawyer Pierce County, at (253) 770-0808.


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