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What is a Nystagmus Test?

A Closer Look at Field Sobriety Tests - Sarasota DUI Lawyer

We are familiar with the sobriety exercises given when pulled over for allegedly drinking and driving. Whether you have been personally involved in a situation like this, or have seen a television show depicting a similar scenario, the sobriety exercises requested are recognizable. But even with this in mind, can you confidently say that you know what is being evaluated by the DUI investigator when he or she is asking you to follow that pen with your eyes or when you are asked to walk that white line? If you or someone you know would like clarification on standardized field sobriety exercises, or the Nystagmus (HGN) exercise, contact a Sarasota DUI lawyer at Pallegar Law, P.A. for more information.

Horizontal Gaze Nystagmus

The Horizontal Gaze Nystagmus (HGN) exercise was created in 1977, where it was introduced as one of the three screening tools used to indicate alcohol impairment. During the HGN exercise, officers are checking for equal pupil size, equal tracking in both eyes, smooth pursuit, sustained Nystagmus at maximum deviation, and Nystagmus onset prior to 45 degrees. The exercise has the ability to tell when a person has used central nervous system depressants, and can be used in the court of law as evidence. This test is 77% accurate according the National Highway Traffic Safety Administration (NHTSA). An experienced DUI Lawyer at Pallegar Law, P.A. would be able to evaluate whether or not a this test was conducted properly.

Nystagmus is a naturally occurring event in all individuals, commonly described as rapid involuntary jerking movements of the eye. Alcohol and drugs enhance the occurrence of Nystagmus and while it is usually unclear to the human eye, a properly trained law enforcement officer can see it when an individual is under the influence. Though, with this training comes the responsibility of carrying this exercise out exactly as directed, or it could be inaccurate and unreliable.

Alcohol can enhance the occurrence of Nystagmus, but did you know there are 75 other exhaustive causes that could lead to it as well? Some of the most common triggers are a high fever, head injuries, vertigo, fatigue, nicotine, and caffeine. In addition to these variables, if the HGN exercise is not conducted properly, it could lead to unclear results. The accuracy could be affected if you were facing the direction of oncoming traffic with car headlights in your face or if the stimulus used (pen, finger, wand) was held too close or too far from your face.

Proper administration of the HGN test can be found in the NHTSA Manual for HGN. It goes as follows:

  • The individual in question should be asked whether or not they wear contacts or glasses and it should be noted within official form.
  • You will then be asked to place your feet together with your hands by your side.
  • You will then be informed that you will be asked to follow a stimulus (pen, wand, etc.) and that while doing so you should not move your head in either direction, only your eyes should follow it. You should then be asked if you understand the instructions or if you need clarification.
  • The officer should then position the stimulus 12-15 inches away from your nose while it sits slightly above eye level.
  • There will be 14 passes after this, measuring equal pupil size, equal tracking in both eyes, smooth pursuit, sustained Nystagmus at maximum deviation, and Nystagmus onset prior to 45 degrees. Each eye must have two passes per segment, and the pass should begin with the left eye, meaning the officer should move the stimulus first to the right. Any test that doesn’t have at least 14 passes and doesn’t take at least 82 seconds starting from the time the stimulus starts moving, has been administered improperly.

Vertical Gaze Nystagmus, VGN, may also be tested at this time. During this test, officers are looking for the same jerking motion when the stimulus is held at maximum deviation.

Walk and Turn

During the Walk and Turn test, you will be provided with instructions and then be asked to perform them on a hard, non-slippery surface. The administrating officer will tell you that during this test, you will need to put your left foot on the line and your right foot in front of it with your heel touching your left toe. He will demonstrate this and remind you to keep your hands by your side. You will walk nine steps forward, turn, and walk nine steps back.

Officers are looking for behavioral indicators that you are under the influence. A few are, not being able to keep your balance while listening to instructions, starting too soon, stopping during the test, stepping off the line, using your arms as a balance, incorrect amount of steps, improper turning, etc.

While the walk and turn test is used a great deal among law enforcement, it is only 68% accurate according to the National Highway Traffic Safety Administration.

One Leg Stand

The One Leg Stand test is the third and final standardized field test that can be used during the course of a drunk driving stop. Before administering the test, the officer should ask you if you have any physical problems or disabilities.

During this test, the officer will ask you to stand with both feet together and with your hands by your side. When he instructs, you will lift either leg, whichever you prefer, 6 inches off of the ground. You will then begin counting and not cease until he tells you to. The test should last at least 30 seconds.

The administering officer is observing to see if you are swaying while balancing, using your arms to balance, hopping, put your foot down.

According to the National Highway Traffic Safety Administration, the One Leg Stand test is the least accurate at 65%.

When dealing with law enforcement, it is recommended you immediately discuss your situation with a trained lawyer. If you do not have one, contact an attorney at Pallegar Law, P.A. and ask for more information on how to move forward with any and all potential DUI affirmative defenses.

Contact a Lawyer at Pallegar Law, P.A. for more Information

If you have been subjected to a Horizontal Gaze Nystagmus (HGN) exercise after a DUI arrest and have questions about whether it was administered properly, contact an experienced Sarasota DUI Attorney. Call 941.893.5816 to schedule your free consultation.

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