What is the horizontal gaze nystagmus test, and is it accurate?

On Behalf of | Oct 1, 2019 | Field Sobriety Tests

You went out for a night with friends, and you had a little too much to drink. Despite knowing that you’d ingested some alcohol, you didn’t think it was enough to make you a dangerous driver.

Several minutes later, you had to swerve to avoid a small animal in the road. Then, you noticed the flashing lights behind you. The police saw your movements but didn’t see the reason for the swerve. They stop you, smell alcohol and ask you to take sobriety tests.

One of those tests is known as the horizontal gaze nystagmus. The horizontal gaze nystagmus test is one that looks for unusual jerking of the eyeball that results in the eyes gazing to the side. Usually, this happens when the eyes are rotated to a high peripheral angel. When you’re intoxicated, the nystagmus is exaggerated and can happen at a much less severe angle.

What do the police look for during a horizontal gaze nystagmus test?

While taking the test, the officer will look to see if your eyes are tracking normally. The officer watches as you follow a slowly moving object as it moves horizontally through your field of vision.

There are three signs of impairment that may appear if you’ve been drinking alcohol including:

  • Being unable to follow the moving object smoothly
  • Having jerking prior to a 45-degree angle
  • Having distinct jerking when the eye is at the maximum deviation from the center

Of all the field sobriety tests, the horizontal gaze nystagmus is among the most accurate. Previous studies have put its accuracy at around 88%. When combined with other field sobriety tests, the accuracy is expected to be even higher.

Can the horizontal gaze nystagmus test be wrong?

Yes. Like all other kinds of tests, this test also has the potential to be inaccurate. Neurological conditions, for example, could make the eyes jerk and make the test inaccurate. That’s why multiple field sobriety tests are used together. Even then, though, there is a chance that the tests will not be correct and that you will be falsely accused of being intoxicated.

If you are stopped and fail this test, it’s in your best interests to put together a strong defense. The officer’s observations or conduct of the test may be inaccurate, but it is still important to take your arrest and any charges that come from it seriously. A conviction could be costly and affect your life, so it’s worth fighting.

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