Answer: The horizontal gaze nystagmus is the first test. And what that test is, nystagmus stands for involuntary jerking of the eye. And what happens is alcohol works on your nervous system and it will affect your vision, so your eyes as they’re taken out to a certain point will begin to bounce or jerk. And the test is designed to have your eyes focus and then move at a certain speed at a certain distance in order to determine if alcohol is present. However, studies have found that there are over 300 causes that can affect your eyes and make you have nystagmus.
The second test is the walk-and-turn which is a divided attention test. And it involves walking in a straight line with your feet heel-to-toe, taking nine steps, turning and returning nine steps with your hands at your side. It is important to say that on all three tests, you are to have the person at a certain position. The start of it is called “locking them in.” And that way it helps because if they start losing their balance, you would know that they’re most likely impaired so they wouldn’t injure themselves. However, with the walk-and-turn, the one requirement by NHTSA, who helped design the test, was that the ground be reasonably flat, you need to be clear of debris. And what you’re looking for is someone stepping off the line or raising their arms more than six inches above their body, unable to count with their head down and making a bad turn where they can’t follow instructions. Or if they start too soon when they’re put in the position, because they’re asked to stand with their right foot in front of their left and they count the first step when they start moving their feet and the trail foot hits the ground the first time.
And the last test is the one-leg stand. And, again it’s a balance test and a divided attention because you have to raise your foot up and keep your hands at your side and count out loud, 1001, 1002 and so on until you reach 30 or the officer stops. It’s a timed test by the officer. They should be timing it for 30 seconds. And they’re looking for you putting your foot down, hopping, swaying or in some cases people just can’t do it at all.
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