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The Horizontal Gaze Nystagmus Test Used in DUI Arrests

If you are pulled over for driving under the influence (DUI), the law enforcement officer will conduct field sobriety tests to determine if you are intoxicated.  One of the tests that may be used is the horizontal gaze nystagmus (HGN) test.  Scientists believe that the HGN test is a reliable way to measure a driver’s impairment from alcohol,  but how accurate is it?

Nystagmus refers to “an involuntary jerking or bouncing of the eyeball that occurs when there is a disturbance of the vestibular (inner ear) system or the oculomotor control of the eye.”  Horizontal gaze nystagmus is defined as the lateral or horizontal jerking when the eye looks to the side.  The reason experts say that the HGN test is a good way to test intoxication is due to the belief that alcohol consumption can hinder the ability of the brain to correctly control eye muscles.  As the degree of impairment increases, so does the amount of jerking or bouncing of the eyeball.

The HGN test is one of the three field sobriety tests used by law enforcement officers.  These tests are used to establish probable cause for DUI arrest.  Most field sobriety tests look at coordination, balance and dexterity, which are reduced when someone has a higher BAC (blood alcohol content).

A police officer can administer the HGN test when a suspect is pulled over for driving under the influence.  During the HGN test, the officer must be able to clearly see the driver’s eyes, even if it means the use of a flashlight.  The driver will be asked to follow an object with his or her eyes, such as a pen or penlight.  The object is generally placed twelve to fifteen inches from the driver’s face and slightly higher than eye level.  At this point, the officer will be looking for various clues that will indicate impairment, including nystagmus.

Results of HGN Tests Can Be Wrong
It is important to note that nystagmus can be caused by other factors besides alcohol consumption.  For example, neural or muscle activity, eye strain, brain damage, brain tumors and inner ear diseases can all lead to nystagmus. 

The results of the HGN test can be inaccurate if the law enforcement officer is not properly trained to administer the test and if there were any underlying health factors.

If you have been arrested for DUI or DWI, you need to have an attorney review your case.  A DUI or DWI conviction carries significant consequences.  Call (888) DWI-ANSWER (394-2679) or (888) DUI-ANSWER (384-2679) today for legal advice from an experienced DUI or DWI attorney.