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The Truth about Horizontal Gaze and Nystagmus Tests for DUI

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While not admissible in Court in PA to prove the level of intoxication, they are used frequently by police to establish roadside probable cause.

By Attorney Elisabeth K.H. Pasqualini, DUI Attorney, Harrisburg, PA

The horizontal gaze nystagmus (HGN) test has been in use for 30 years, but it has not been widely applied in the United States until recently.  In the United States, California police first noticed during the 1960s that barbituate users' eyes moved in quick jerks, the so-called "barb bounce."  The test was apparently introduced by law enforcement agencies in the western states, and later was employed in drunk driving prosecutions in eastern jurisdictions. The United States Department of Transportation National Highway Traffic Safety Administration Bulletin DOT HS 806 512 outlines the appropriate procedures for administering the test.  The HGN test is useful in detecting both alcohol and drugs, and is especially valuable because it detects lower levels of intoxication.  Nystagmus is an involuntary jerking of the eyeball. The jerking may be aggravated by central nervous system depressants such as alcohol or barbituates. Horizontal gaze nystagmus is the inability of the eyes to maintain visual fixation as they are turned to the side.

In the HGN test the driver is asked to cover one eye and focus the other on an object-usually a pen-held by the officer at the driver's eye level. As the officer moves the object gradually out of the driver's field of vision toward his ear, he watches the driver's eyeball to detect involuntary jerking. The test is repeated with the other eye. By observing: (1) the inability of each eye to track movement smoothly; (2) pronounced nystagmus at maximum deviation; and (3) onset of the nystagmus at an angle less than 45 degrees in relation to the center point, the officer can estimate whether the driver's blood alcohol content exceeds the legal limit.

Like other roadside sobriety tests, the HGN test has been held to be a "search" within the meaning of the Fourth Amendment, but not to require probable cause to search, so that the application of the test is justified by a police officer's reasonable suspicion, based on specific, articulable facts, that the driver is intoxicated. There is no constitutional requirement that police officers, before administering the HGN test, advise the motorist of his or her rights in accordance with the decision in Miranda v Arizona, because the Miranda rule applies only to testimonial disclosures, and Miranda warnings are not necessary before conducting field sobriety tests such as gaze nystagmus tests.  However, before HGN test results may be received in evidence, a proper foundation must be laid as to the testing techniques and the police officer's qualifications to conduct the test.  Horizontal gaze nystagmus test results have been held or recognized as being properly considered as a factor tending to show probable cause to arrest a motorist for violation of an impaired driving statute. Police officer's testimony as to motorist's blood-alcohol content (BAC) on sole basis of results of horizontal gaze nystagmus (HGN) test was inadmissible.

Horizontal gaze nystagmus (HGN) field sobriety test results cannot be used to quantify or estimate blood alcohol concentration (BAC) in a driving under the influence of intoxicant (DUI) prosecution in the absence of a chemical test.

If you've been arrested for a Driving Under the Influence, you should contact an experienced attorney before going to court.  Do not go to court without counsel.  Contact Shaffer & Engle Law Offices, LLC toll free or email us today.

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