Interviewer: How is the Horizontal Gaze Nystagmus test performed?

Michael Munoz: Horizontal Gaze Nystagmus is a test where they look at your eyes and Nystagmus is involuntarily twitching of the eyes.  The best way to describe it is as this: When someone’s impaired and they look from right to left or left to right at a certain speed, their eyes may not move fluidly, they may twitch kind of like when you turn on the windshield wipers on a dry window, how those skip, that’s kind of how your eyes will look if you’re impaired. The officers are looking for three clues and they’re looking for three stages where they see twitches.

Police Officers Look for Clues to Determine the Presence of Nystagmus in the Subject

The officers are supposed to put out a stimulus in front of someone, move the stimulus back and forth slowly over a specific amount of time at a specific distance from the person’s face. The person is supposed to look straight without moving their head and moving their eyes only watching the tip of the stimulus and then, the officers are supposed to look.  In addition, the suspect who’s having the test done to them is supposed to not have any flashing, blinking, bright lights in their face while they’re conducting the test because that can throw off the test. What the state tries to do is they try to say that if they find all clues of the HGN, they will argue that science says that they must be an 0.08 or over blood alcohol level.

The Horizontal Gaze Nystagmus Test Must be Administered While the Subject is Standing Upright

Interviewer: Does Horizontal Gaze Nystagmus have to be performed as the individual is sitting down or standing up?

Michael Munoz: Standing up.  The officers have to go through a training course, they have to have a certain accuracy level. Most of the officers that conduct Horizontal Gaze Nystagmus are also DRE officers, Drug Recognition Experts as well.

The Other Factors Which May Cause the Occurrence of Nystagmus in an Individual

Interviewer: Could there be any other factor that can create this effect, like natural occurring nystagmus for instance?

Michael Munoz: Yes.  There are a number of things that can occur that can make you show those symptoms of involuntary twitching of the eyes.  Alcohol is one of many things, a prior concoction, a recent concoction and actually a neurological disorder that you might have not known about, you could have a tumor, you could have other physical conditions that causes it.  There are a number of things that can cause Horizontal Gaze Nystagmus that has nothing to do with alcohol or drugs.

Naturally Occurring Nystagmus Can be Challenged in Court as it is Not Related to Alcohol or Impairment

Interviewer: So, that’s definitely something that can be argued, you know.

Michael Munoz: Yes.  That is one of the defenses is to explain to the jury that Horizontal Gaze Nystagmus does not mean you’re impaired by alcohol; it means that you may be impaired by alcohol but that’s one thing of which could be — there could be many other things that make your eyes do that.

By Michael Munoz

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