WTF is the “Horizontal Gaze Nystagmus”?

WTF is the “Horizontal Gaze Nystagmus”?

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It’s not a distant planet. It’s not a Kama Sutra move. It’s a DUI field sobriety test. And it’s coming to hipster parties near you.

The Horizontal Gaze Nystagmus is one of many field sobriety tests given by law enforcement to determine whether you are under the influence of alcohol. “Nystagmus” means a jerking of the eyes from side to side, and police officers use clues about how and when the eyes are moving or jerking to determine your level of alcohol intoxication (if any). Below is the basic nuts and bolts of the Horizontal Gaze Nystagmus test, affectionately referred to as “HGN.”

The Test: During the nystagmus test, you’ll be instructed to keep your head facing straight ahead, while following an object with your eyes. The object that you must keep your eyes on is usually a pen or a pencil, or if it’s nighttime, the officer will use a small penlight. The officer is supposed to move the pen in a level, even arc to the side of your head. There are 3 main ways the officer measures nystagmus:

#1 – Angle of Onset: While giving the test, the officer will observe the “angle of onset” of the nystagmus. Research has shown that the sooner your eyes begin to jerk, the more intoxicated you are. There is even a magical formula for calculating your blood alcohol content level by subtracting the angle at which your eyes begin jerking from the number 50, and then converting it to a percentage. So if you’re staring straight ahead at an angle of 0 degrees, and after following the officer’s pen your eyes begin jerking at a 45 degree angle, then you supposedly have a blood alcohol content level of 5% or .05.

#2 – More Distinct At the Lateral Extreme: If the eyes are moved to the “lateral extreme,” which means beyond the periphery, and the nystagmus becomes “more distinct,” this indicates alcohol intoxication.

#3- Lack of Smooth Pursuit: If your eye “jumps” or “tugs” while following the pen rather than following it smoothly, then this indicates alcohol intoxication.

Let’s be honest here. This HGN test is subject to numerous flaws. The officer is supposed to keep his hand steady, move the pen in a smooth arc, keep the pen between 12-15 inches from your face, and make a guess at the angle at which your eyes are jerking. That’s a lot for an officer to juggle at one time.

What if you took some aspirin that night? That can cause nystagmus. Some people have natural nystagmus, what about them? Did the officer hold the pen steady for at least 2 seconds when your eyes began jerking? Well, he was supposed to.

Being charged with a DUI can be a very stressful process. Remember that you’re innocent until proven guilty, not the other way around. Cops are people too and are sometimes tired, lazy, prejudiced, and forgetful. They often cut corners and aren’t going to ensure your rights are protected.

If you want to talk to me about your DUI, please feel free to call me at 310-200-4519, email me at, or contact me through my website.

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