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What is Horizontal Gaze Nystagmus?

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What is Horizontal Gaze Nystagmus?

Kevin:   I’m here with DUI professional, Charlie Smith. Charlie, I get a lot of questions regarding being arrested for a DUI. Usually, prior to arresting you, a law enforcement officer will ask you to stare at a pen, pencil, or a red light that they move from side to side. They call this HGN, horizontal gaze nystagmus. I have two questions for you. First of all, what is it and secondly, what does it do?

Charlie:    Horizontal gaze nystagmus is an involuntary jerking of the eye when the vestibular system has been disrupted. Alcohol, as well as certain types of drugs, will disrupt that and HGN will be present. Now when the officer administers HGN, first they must qualify the person for the test by simply saying I am going to check your eyes. If you wear glasses, they will ask if you can see without your glasses on. Then they will ask you to remove your glasses. If you are not wearing glasses, they will ask if you are wearing contact lenses. If you are wearing contact lenses; it used to be asked if the contact lenses were hard or soft. Everyone wears soft contacts now. But years ago with hard contact lenses, if you rotated your eye too far to the side, you would end up looking for your contact lens because it would have popped out. But what they are looking for is an involuntary jerking of the eye as an object moves across the field of vision. So what is happening is stop, focus, stop, focus and that is called the involuntary jerking of the eye. The best way to describe that is a pair of windshield wipers on a dry window, they will bounce along as they cross the windshield and that is what they are looking for. That is the eye going stop, focus, stop, and focus all the way across the field of vision. This is called a lack of smooth pursuit where the eyes track together. 

Next, is maximum deviation where they take the object and move it out to the extreme, about 50 degrees roughly, past your shoulder. Your eye is rotated all the way to the left or the right, and there is just a very little bit of white left in the corner of the eye, like a thumb nail left in the corner of the eye. If the eye continuously drifts at that point then they call it maximum deviation. That is one of the clues the officer is looking for. Now the officer brings the object back to the center and does it very slowly, because they are looking for that first drift of the eye which is the angle of onset. When the officer sees that first drift they stop to see if the eye continuously drifts at the point. If it does not, then the officer moves the object a little bit more until the next drift and then they hold it there. What the officer is looking for is called an angle of onset. All this test does is determine if the person consumed some alcohol and/or possibly some drugs that would cause horizontal gaze nystagmus to be present.   

Kevin: Why is horizontal gaze nystagmus important and how is it used by the law enforcement officer?

Charlie: The test determines if there is involuntary jerking of the eye, in which case there is something causing disruption in the vestibular system. That is most likely alcohol and that is what the law enforcement officer is looking for. HGN is one of the best indicators of alcohol and what they call PAN or Positional Alcohol Nystagmus. That is the best indication of alcohol being consumed, so that is what the officer is looking for. Not impairment, no way an impairment, but consumption. HGN is the best way to determine that. 

Kevin: If you have been arrested for a DUI and you were subjected to HGN testing and indeed had HGN, we now know that it stands for horizontal gaze nystagmus. It is a tool that it used by a DUI officer as a screening tool to determine whether or not you have consumed any alcohol. It may show that your eyes will actually lack smooth pursuit or the eyeball will jump as it tracks from side to side. This may be an indication that you have consumed alcohol, although it is not an indicator that you are impaired. This is a tool used by law enforcement in order to affect an arrest for DUI.            


The criminal defense attorneys at Carlson, Meissner, Hart & Hayslett, P.A., fighting for our clients rights in criminal defense cases in ClearwaterTampaBradentonSpring Hill, Pinellas, Pasco, New Port Richey, Manatee, Hillsborough and Hernando Counties in Florida. 

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J. Kevin Hayslett

Kevin Hayslett, Esq.

J. Kevin Hayslettis an attorney practicing in the areas of Criminal Defense and DUI Defense from the Clearwater office and Hillsborough office. Kevin is an avid tennis player and is currently nationally rated in singles and doubles. You can follow Kevin onGoogle+, oron Radio IO on his show, "Kevin's Law". Kevin can also be heard on the Sirius Satellite Radio show during the "Ask the Lawyer" segment, which can be heard the first Thursday of every month.