The horizontal gaze nystagmus (HGN) test is one of the standardized field sobriety tests. This test gets its name fromhorizontal gaze nystagmus which refers to a quick movement or jerking of the eye as it moves side to side. … First, the police officer checks each eye for lack of smooth pursuit.

The National Highway Traffic and Safety Administration (NHTSA) designed three standardized testing methods that can be implemented by law enforcement officers nationwide and are used to assess a person’s level of intoxication. These are known as field sobriety tests and they are simple ways of testing the physical and cognitive skills of any individual who has been suspected of driving under the influence.

Nystagmus is the medical term used to describe the involuntary jerking of the eyeballs. When someone is intoxicated by alcohol and/or certain drugs, this jerking becomes more pronounced. As such, the horizontal gaze nystagmus test is used by law enforcement agents to evaluate an individual’s nystagmus in order to determine if probable cause exists for a drunk-driving arrest.

Horizontal Gaze Nystagmus Test Procedure

Prior to administering the horizontal gaze nystagmus test, the officer will evaluate your eyes to look for resting nystagmus, equal pupil size and equal tracking (that is, if both eyes can follow an object together). If any of these factors are exhibited, there is chance of an existing medical condition or injury that will render the test unreliable.

To administer the test, the officer will hold a small object approximately 12-15 inches from your nose and slowly move it from one side to the other. You will follow the object with your eyes while keeping your head still.

The officer will look for three different clues in each (for a total of six) during the test. One is lack of smooth pursuit—are the eyes jerking or bouncing while following the stimulus? Next, the officer will look for nystagmus that sets in before the eyes reach a 45 degree angle. The last clue is nystagmus at maximum deviation, which means that the eyes begin jerking within four seconds while looking all of the way to the side.

If the officer observes four or more clues, he or she has probable cause to make an arrest for driving under the influence.

Challenging the Horizontal Gaze Nystagmus

Even when administered in the most ideal of scenarios, the horizontal gaze nystagmus is only 77% accurate in determining if an individual is impaired. Not only that, but there are numerous neurological, medical and eyes conditions that could cause the onset of nystagmus—which is something only a doctor, not a police officer, could determine.

The Horizontal Gaze Nystagmus (HGN) test is often the first one used to assess a person’s level of intoxication. Horizontal gaze nystagmus is the term used to describe the involuntary jerking of a person’s eye which can occur when one’s gaze is cast to the side. Nystagmus is used as an indicator of impairment because it becomes exaggerated when intoxicated and can occur at lesser angles than those that would normally provoke an eye jerk. Typically, an officer will move a flashlight or lighted pen and ask the suspect to follow the light with their eyes. This allows the officer to track the eye movement of the suspect and identify whether or not they are able to accurately follow a slowly moving object without any eye jerking or deviation. When an individual is unable to complete the light tracking without faulty eye movement, officers may have further reason to assume that the suspect has been driving under the influence. While NHTSA research has found that about 88% of persons who show signs of horizontal gaze nystagmus are also intoxicated, it cannot be assumed that this is the only cause. The failure in this test lies in the fact that nystagmus is a common clinical condition that plagues several thousand people throughout the U.S. Furthermore, it often goes unrecognized and undiagnosed. Therefore, it could be argued that the field sobriety test involving HGN is not a great way to identify intoxication, as the results of the test could simply signify that the person suffers from a nystagmus condition.

The second standardized test used by police officers during a roadside check for sobriety is the Walk and Turn test. This is a type of “divided attention” test which requires a driver to utilize both listening/ comprehension skills as well as physical capabilities; the theory being that impaired persons are unable to divide their skills between mental and physical tasks. When a suspect is directed to perform the Walk and Turn test they will be asked to take heel-to-toe steps along a straight, linear path. After a certain amount of steps have been taken in one direction, the individual will then be asked to turn around on one foot and repeat the heel-to-walking in the other direction. Among the indicators that officers will be looking for during this type of test are a suspect’s ability to keep balance, turn properly, take the correct number of steps in the correct way (i.e. heel to toe), stay on the linear path, walk the line without using arms to balance, and listen to and follow instructions properly. However, it can be more than difficult for even unimpaired individuals to successfully follow some of these procedures. Therefore, relying on the indication of two more of these signs for confirmation that a person’s cognitive and mental skills are impaired is an unsafe way to determine impairment.

The third of the standardized tests is the One Leg Stand test. Like the Walk and Turn test, this is one that focuses on the ability of person to utilize their divided attention skills. Upon being pulled over, an officer may ask the driver to stand with one foot on the ground while the other is held approximately six inches off the ground. At the same time, suspects will be asked to count by thousands while the officer conducting the test records signs of impairment for a period of 30 seconds. During this timed event, law enforcement officials will be looking for indicators such as swaying, unsecure balance, hopping to maintain stance, using arms to help with balance, and putting your raised foot down. According to NHTSA, a little over 80% of persons who exhibit two or more of these behaviors during their performance of the One Leg Stand will have a blood alcohol concentration level above the legal limit. Again, what is failed to be mentioned is the fact that this can be a less than easy task for anyone, sober or not. Some people naturally have a more difficult time maintaining their balance in even the most normal of circumstances, making an on-the-spot test of balance one that could yield inaccurate results.

The inadequacy of these standardized tests has not failed to be recognized. In fact, other non-standard tests have been put in place to supplement those implemented by the National Highway Traffic and Safety Administration. The Rhomberg Stationary Balance Test requires drivers to stand with feet together while leaning back to look up at the sky and holding their arms out to the side. The Finger-to-Nose Test asks suspects to close their eyes and then touch their nose with their pointer finger. These, along with standardized test methods, are believed to be the clearest ways to quickly identify alcohol or drug impairment. Unfortunately, they are also tasks which many non-intoxicated individuals would be unable to complete if asked to do so. Therefore, their accuracy is less than reliable and should not be used as a primary source of intoxication identification. If you have recently been arrested based on your performance of a field sobriety test such as those described above, then you should most definitely challenge the charges that have been brought against you. With the help of a DUI defense attorney you can use the inaccuracies of these methods to prove that your DUI arrest was not founded on sound evidence and should not lead to a conviction.