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Why do police officers check your gaze during a DUI stop?

Whether it was on a television show or you experienced it in real life, most people are familiar with the three tests that are given to most drivers during a field sobriety test. The first two are typically the one-leg-stand tests and the walk-and-turn test. But it’s the third of these tests that we’d like to take a closer look at in today’s post.

Called the horizontal gaze nystagmus test, this test typically requires a driver to follow a light or pen being held and controlled by the officer. The officer will ask the participant to follow the object from side to side. But what is the point of this test, you might ask? Well, it actually has to do with how alcohol affects the muscles in your eyes and it’s actually an effect officers can see.

Let’s take a look.

When a person consumes alcohol or other depressants that affect the central nervous system, the substance interferes with the brain’s ability to control muscles in the eye. When you move your eyes to the side, your muscles have difficulty controlling the movement, which appears to the officer as a horizontal or lateral jerking motion. As the National Highway Traffic Safety Administration explains, the greater the degree of impairment, the more pronounced the nystagmus — or jerking — becomes.

Because research has shown the reliability of this test time and again, officers across the nation frequently use it in field sobriety tests to determine if a driver is intoxicated or not. It’s worth pointing out however, that if an officer is not trained on how to properly administer this test, the reliability of this test becomes irrelevant because the test results may be off or incorrect altogether. This is something not only drivers should keep in mind but courts as well because this could mean the difference for someone accused of drinking and driving.



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