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Field Sobriety Eye Test (HGN)

When the police stop someone suspecting that they may be Driving Under the Influence of alcohol or drugs, one of the things the officer will do is ask the driver to step out of the vehicle to perform several Field Sobriety Tests. These tests are used by police as an investigative tool to determine whether a driver may be under the influence of drugs or alcohol. Law enforcement officers may use any number of field sobriety tests, but there are only three standardized field sobriety tests (SFSTs). The Horizontal Gaze Nystagmus Test (HGN) test is one of the three standardized field sobriety tests supported by the National Highway Traffic Safety Administration (NHTSA).

What is the Horizontal Gaze Nystagmus test?

The Horizontal Gaze Nystagmus Test is an eye test where an officer looks for nystagmus –– the involuntary jerking of the eyeball. This is done by asking the driver to follow an item such as a pen, flashlight, or a finger with their eyes, back and forth. The angle at which the eye begins to demonstrate nystagmus is noted, as well as the degree of maximum deviation.

What are the police looking for?

Police officers are trained to perform the HGN while noting the angle at which nystagmus occurs. The pen or other stimulus is supposed to be tracked slowly to the right and left, horizontally. Nystagmus occurs naturally when the eyes are rotated at high angles. Yet when a person is impaired due to alcohol consumption, the jerking may occur at a lesser angle. Based on this, police look for three things during an HGN test.

  1. The lack of smooth pursuit;

  2. If there is distinct jerking when the eye is at the maximum rotating deviation; and

  3. If the angle of onset jerking is within 45 degrees of the center.

Basis for HGN Tests

Alcohol has an effect on motor control systems in the body, and can reduce coordination, and slow reflex and response times. It also affects the nervous system's control of eye movements. NHTSA considers the test the most accurate of the three SFSTs (the other two being the Walk and Turn Test, and One Leg Stand Test).

While there are several types of nystagmus, alcohol affects two types: alcohol gaze nystagmus (which includes HGN), and positional alcohol nystagmus. Only alcohol gaze nystagmus is tested as an SFST. Eyes normally track moving objects smoothly. However, under the influence of alcohol, the eye following the object begins to lag behind, and through jerking motions, catches up to following the object. This is an involuntary motion, and the person showing nystagmus cannot control it, and is unaware of the jerking motion their eye is demonstrating.

How Police are Trained

NHTSA has noted the importance of proper training in SFSTs in order to ensure the accuracy of the test. Formal training in SFSTs was introduced to teach police how to more adeptly detect impaired drivers. The International Association of Chiefs of Police (IACP) handles the administration and accreditation of training programs. However, just because an officer may have been properly trained in SFSTs, does not mean that they correctly administered or observed the test.

SFST training, including administering the HGN eye test, is highly specific and specialized. Some attorneys specializing in DUI defense have taken these same training courses in order to place themselves in a better position to question, cross-examine, and analyze a police officer's SFST findings.

Proper Administration of the HGN Test

Even though officers are trained in administration of these standardized tests, many of these officers conduct hundreds of SFSTs.  As a result, they may not always give the standardized instructions, or they may incorrectly administer the test. Additionally, if they suspect a person to be intoxicated, they may not accurately observe the individual completing the test. When an officer has not properly instructed a suspect, or not properly observed the test, this information can be utilized by a skilled DUI defense attorney.

The test is to be administered in a well lit area, or using a flashlight so that the subject's eyes can be seen clearly. The subject should not be facing the flashing lights of the police car, or the headlights of other cars. The subject should not be wearing eyeglasses, for better observation. The officer is supposed to tell the subject they are going to check their eyes, and ask if they have any medical impairment which could affect the results. The object observed should be placed 12 to 15 inches from the subject's face and just higher than eye level.

Do I have to do the HGN test?

You can refuse to take the HGN test, as well as any or all of the field sobriety tests. However, this does not mean that you will not be arrested. The SFSTs are used as investigative tools. If you refuse the test, but the officer still believes you are impaired, you will likely be arrested and taken to the police station where they will conduct a chemical test to determine your blood alcohol content.

Limitations of the HGN Test

An HGN test does not only identify intoxicated persons, it may incorrectly identify people under seizure medication as being intoxicated. If it is not properly administered, a number of factors could make it appear that the subject failed the test. Among other things, the flashing police lights or the headlights of a passing car may trigger a nystagmus unrelated to alcohol.

Defenses to the HGN Test

The police, prosecutors, and NHTSA may say how accurate the HGN test is, but it is still not 100% accurate. In fact, many medical experts disagree on the accuracy of the HGN test. Additionally, it is a police officer performing the test, with only a few days of training attempting to diagnose the HGN angle, and level of nystagmus rather than a medical professional. A lawyer specializing in DUI defense will be able to identify which defenses to use, to get charges reduced or dropped.

Experienced DUI Attorney Representation:

If you are arrested for a DUI anywhere in Alameda County or Contra Costa County, Lynn Gorelick is familiar with the local drunk driving and DUI laws, and how police gather evidence during traffic stops. She is trained in all field sobriety testing, including the HGN test. She knows the local prosecutors, judges, and officers involved.  With over 30 years of DUI experience, Lynn Gorelick understands the law and the science required to fight driving under the influence, and other alcohol charges.  

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