What Is The Horizontal Gaze Nystagmus Test?

Field sobriety tests are used by Texas law enforcement officers to identify drivers who are operating vehicles under the influence of alcohol or drugs. While there are a range of tests that can be employed, one of the most reliable and scientifically supported field sobriety tests is the Horizontal Gaze Nystagmus (HGN) test.

For individuals suspected of drunk driving, it is important to be aware of the role and administration of HGN tests and other field sobriety tests. Consult with an experienced Houston DWI lawyer to ensure your rights are protected. Skilled legal professionals who have connected past clients with favorable outcomes can provide you with the best possible defense.

What Is the Science Behind HGN Tests?

When people refer to the results of a Horizontal Gaze Nystagmus test, they’re referring to the involuntary jerking of the eyes that occurs as they gaze to the side. This jerking becomes more pronounced when a person is impaired by alcohol or certain drugs. During the HGN test, an officer will instruct the suspect to follow a stimulus, usually a pen or a small flashlight, with their eyes as it is moved slowly from side to side. The officer then looks for indicators of impairment, such as the inability to smoothly follow the stimulus.

The science of HGN tests is based on the fact that alcohol impairs the brain’s ability to control eye muscles, leading to noticeable jerking movements. These movements can be detected at blood alcohol concentrations (BAC) as low as 0.04 percent.

How Often is the HGN Test Used?

The HGN test is widely used by law enforcement agencies across the United States, including in Texas. In addition to the HGN test, individuals suspected of driving under the influence may be asked to perform other field sobriety tests as well.

• Walk-and-turn. In this test, the suspect is instructed to take steps, heel-to-toe, along a straight line, turn on one foot, and return in the same manner. Officers observe if there are any balance issues, an inability to follow instructions, or other signs of impairment.
• One-leg stand. Law enforcement may ask the individual to stand on one leg and count aloud for about 30 seconds. Swaying, using arms for balance, hopping, or putting the foot down are signs of impairment.
• Preliminary breath test. Although not a field sobriety test per se, officers might use a portable breathalyzer to estimate the suspect’s blood alcohol level.

The results of all of these tests can support a prosecutor’s case as results are generally admissible in court. Officers trained in administering the HGN test can testify about their observations, providing compelling evidence of impairment. Anyone who is charged with drunk driving or operating a vehicle while under the influence of drugs should talk to a skilled Houston DWI lawyer as soon as possible.

Was a Horizontal Gaze Nystagmus test administered before you were arrested? Developed through scientific research and widely implemented, these tests are often used by prosecution teams. To begin the process of building a defense, contact Ayson Law Firm.