The horizontal gaze nystagmus test is one of three standardized field sobriety tests that the police routinely use whenever they suspect a driver is drunk, drugged or both.
Here’s why you should think twice about agreeing to subject yourself to it — even if you’re certain you’re sober.
How does the horizontal gaze nystagmus test work?
Basically, the test checks for nystagmus, or an involuntary movement and jerking of the eyes. To perform the test, the officer will usually hold a pen or a light about a foot away from your face at eye level and slowly move the object from side to side while you are supposed to follow it with your eyes (without moving your head). If your eyes “bounce” or jerk while you try to follow the object, that equals a “fail.”
Why is the horizontal gaze nystagmus test so easy to fail?
Nystagmus is a common problem when someone is intoxicated or high, and it’s what can make it very difficult to focus your vision when you are. It’s also a common problem for a lot of other mundane reasons, like the following:
- The officer moved the object too fast or put it too close to your face.
- You have a bad cold or an inner ear infection.
- Your eyes are simply tired from staring at a computer screen all day.
- You’re on certain medications, including allergy meds.
- You have a medical condition that affects your muscular activity.
Field sobriety tests get a bad rap — for good reason. They’re highly subjective and unreliable, and the officers performing the tests are doing so under less than ideal conditions, making them error-prone, at best. They’re not even usually considered admissible as evidence in court. You can refuse to take one.
So why do the police do them? Because, if you fail, it gives them probable cause to demand a chemical test like a Breathalyzer to check your blood alcohol content. In other words, once you take the horizontal gaze nystagmus test, you’re one step closer to a drunk driving arrest.
