What is the horizontal gaze nystagmus test?

| Sep 19, 2018 | Field Sobriety Tests

If you were pulled over for suspected drunk driving and officers administered the standard roadside field sobriety tests, one of them was the horizontal gaze nystagmus (HGN) test. This may have just seemed like an officer was shining a light in your eyes and asking you to follow their finger. How could that determine whether you were under the influence, and can it be used in court to convict you?

First, it’s important to understand what HGN is. It’s an involuntary motion of the eyes when they move sideways that increases when a person is under the influence of alcohol and certain drugs. You can’t “fake” your way out of an HGN test because you don’t know you’re doing it.

The National Highway Traffic Safety Administration (NHTSA) has long considered the HGN test to be the most accurate of the three most common field sobriety tests — more so than the walk-and-turn and one-leg stand tests. Together, the three have been shown to have an 83 percent accuracy rate in spotting people with blood alcohol concentration (BAC) of at least .10 percent.

Just like Breathalyzer test results and other evidence, an attorney may be able to challenge the results of an HGN test in court. Officers have to be trained in how to conduct the test and to follow the correct procedures.

For example, they need to make sure that the person to whom they’re administering the test is facing away from the police car’s lights and not impacted by the lights of other vehicles in the area. Further, there are other things besides alcohol and drugs that can impact a person’s HGN, such as fluid in the inner ear and even eye strain.

If you or a loved one is facing DUI charges, it’s important to know that you have a right to challenge all evidence against you, including the calibration of the Breathalyzer and how any field sobriety tests were administered. An experienced Maryland DUI attorney can provide valuable guidance and work to protect your rights.

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