Horizontal Gaze Nystagmus (HGN)

Horizontal Gaze Nystagmus (HGN)

Horizontal gaze nystagmus (HGN) is a type of field sobriety test that is commonly used by law enforcement officers to detect impairment due to alcohol or other drugs. The HGN test is based on the observation of involuntary eye movements that can be caused by alcohol and other drugs. In this article, we will explore the history, procedure, and controversies surrounding the HGN test.

Police officer giving a field sobriety test to a drunk driver.

History of the HGN Test

The HGN test was first introduced as a field sobriety test in the early 1980s by Dr. David Marcelline, a medical doctor who specialized in forensic toxicology. Marcelline had observed that alcohol and other drugs could cause involuntary eye movements, or nystagmus, in people who were impaired. He developed a standardized test that law enforcement officers could use to detect nystagmus in drivers who were suspected of driving under the influence.

In the years that followed, the HGN test became widely used by law enforcement officers across the United States. In 1995, the National Highway Traffic Safety Administration (NHTSA) included the HGN test as one of the three standardized field sobriety tests recommended for use by law enforcement officers. Today, the HGN test is considered to be one of the most reliable and accurate field sobriety tests for detecting alcohol and drug impairment.

Procedure of HGN Test

The HGN test involves the observation of involuntary eye movements as a driver follows a moving object, such as a pen or flashlight, with their eyes. The officer holds the object about 12-15 inches from the driver’s face and moves it from side to side. The driver is instructed to keep their head still and follow the object with their eyes only, without moving their head.

The officer observes the driver’s eyes for three signs of nystagmus: lack of smooth pursuit, distinct nystagmus at maximum deviation, and onset of nystagmus prior to 45 degrees. Lack of smooth pursuit means that the driver’s eyes are not able to smoothly follow the object and may jerk or bounce as they try to track it. Distinct nystagmus at maximum deviation means that the driver’s eyes cannot move any further to the side without jerking. Onset of nystagmus prior to 45 degrees means that the driver’s eyes start jerking before they have moved the object 45 degrees to the side.

If the officer observes four or more clues of nystagmus in both eyes, this is considered a strong indication of impairment due to alcohol or other drugs. If the officer observes two or three clues, this is considered a weaker indication of impairment.

Controversies Surrounding HGN Test

Despite its widespread use, the HGN test is not without controversy. Some critics argue that the test is not reliable or accurate, and that it can be influenced by factors such as the officer’s training, the driver’s physical condition, or the conditions in which the test is administered. In addition, some studies have suggested that the test may not be accurate in detecting impairment from drugs other than alcohol.

Another controversy surrounding the HGN test is the question of whether drivers have the right to refuse to take the test. In many states, drivers are required to submit to a breathalyzer test if requested by a law enforcement officer. However, the rules surrounding the HGN test are less clear, and some drivers have argued that they should not be required to take the test if they believe they may incriminate themselves.

Critics of the HGN test have also raised concerns about the training and qualifications of law enforcement officers who administer the test. The NHTSA recommends that officers receive extensive training in the administration of the HGN test, but some critics argue that this training is inadequate or that officers may