The horizontal gaze nystagmus (HGN) test is one of the most common field sobriety tests in use today. Supposedly, it’s a “standardized” method of helping police officers determine when a suspect may have been drinking. Fail it, and you’ll probably be asked to take a Breathalyzer exam — or you may be arrested for suspected drug or alcohol intoxication purely on the officer’s assessment of your condition.

Here’s the problem: Field sobriety testing of any kind can be deeply flawed. Not only are tests performed under less-than-ideal conditions (when you’re nervous, stressed and standing at the side of a possibly busy road), the people judging your responses aren’t necessarily objective — or even sure what they’re doing.

When the horizontal gaze nystagmus test is performed, the officer will ask you to follow their finger, a pen or light with your eyes while you hold your head still. They’re watching for any kind of involuntary eye movement or “jerking” of your eyes as you do it. Since alcohol and drugs can affect your ability to control the smooth movements of your eyes, it’s considered evidence that you may somehow be impaired.

The only problem is that you can fail the HGN test for a whole lot of common reasons, none of which have anything to do with drugs or alcohol. Some of those reasons include things like:

  • Stress, including anxiety
  • Allergies to air pollution
  • Excess caffeine consumption
  • Dry eyes
  • Numerous neurological conditions
  • Inner ear problems
  • Brain damage


In fact, one of the most common reasons for jerky eye movements is something that almost anybody can experience: fatigue, like the kind that you may experience after a long day at the office.

A drunk or drugged driving charge is a very serious thing in Missouri. Find out more about how to mount an aggressive defense.