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What is Horizontal Gaze Nystagmus Testing in a DUI Case?

What is Horizontal Gaze Nystagmus Testing in a DUI Case?

Horizontal gaze nystagmus (HGN) testing is a widely used method for determining whether a person is under the influence of alcohol or certain types of drugs. The test is based on the observation of an involuntary jerking of the eye that occurs when the eye is rotated horizontally. The presence and severity of this jerking can indicate the presence of alcohol or drugs in the bloodstream.

The HGN test was first developed in the 1970s by a team of researchers led by Dr. Marceline Burns at Southern California Research Institute. The team was working under a grant from the National Highway Traffic Safety Administration (NHTSA) to develop a standardized field sobriety test that could be used by police officers to detect drunk drivers.

The HGN test is one of three tests that make up the Standardized Field Sobriety Test (SFST) developed by NHTSA. The other two tests are the walk-and-turn test and the one-leg stand test. Together, these tests are designed to measure a person's balance, coordination, and ability to follow instructions, all of which can be impaired by alcohol or drugs.

The HGN test is performed by having a suspect follow a small object, such as a pen or flashlight, with their eyes as it is moved horizontally. The officer conducting the test looks for three specific clues:

An involuntary jerking of the eye as it approaches the center position

Onset of nystagmus prior to 45 degrees of lateral gaze

Distinct and sustained nystagmus at maximum deviation

Each of these three observations (called clues if they are seen), could be present in each eye. There are a total of six possible clues in the HGN test (3 possible clues x 2 eyes). Four or more clues is considered a "failing" test, indicating a likelihood of blood alcohol of 0.08 or higher.

The test has been adopted and widely used by law enforcement agencies throughout the United States. However, the HGN test is not without controversy. Critics argue that the test is not always accurate and can be affected by factors such as fatigue, certain medical conditions, and certain types of contact lenses.

It's important to note that HGN test is not a definitive test for determining whether a person is under the influence of alcohol or drugs, it is simply an indicator. Results of HGN tests should be used in conjunction with other evidence, such as a person's behavior and performance on other field sobriety tests, to determine whether a person is under the influence of alcohol or drugs.

While the HGN test has been a valuable tool in the fight against drunk driving, it's important to understand that it's not a perfect test, and it must be used in conjunction with other evidence to ensure that people are not falsely accused of being under the influence. The HGN test can only show a symptom of alcohol or certain types of drugs in someone's system. HGN does not affect vision, and the presence of HGN, by itself, has nothing to do with someone's ability to safely drive an automobile.

Attorney James R. Snell, Jr., has been trained in the proper administration of the Horizontal Gaze Nystagmus test, along with the other standardized field sobriety tests. In addition to completing the standard training, he completed additional training to become a qualified field sobriety test instructor. Mr. Snell is also the author of the book, South Carolina DUI Defense: The Law and Practice. If you're facing any DUI charge in South Carolina contact our office for a free consultation.


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