Understanding the Horizontal Gaze Nystagmus Test in DUI Field Sobriety: A Guide by Arja Shah

The Investigative Article: Examining the Horizontal Gaze Nystagmus Test in DUI Field Sobriety

Driving under the influence of alcohol or drugs can have fatal consequences, leading to injury or even loss of life. Therefore, law enforcement agencies across the world have implemented a range of tests to detect drivers who may be under the influence of drugs or alcohol. One such test is the Horizontal Gaze Nystagmus test. While this test is widely used, its accuracy has been questioned, prompting us to investigate the test, what it involves, and the related rights of those suspected of DUI.

What is the Horizontal Gaze Nystagmus Test?

The Horizontal Gaze Nystagmus (HGN) test is a field sobriety test that involves a police officer checking the eyes of a suspected DUI driver for any signs of intoxication. The test requires the driver to follow an object, such as a flashlight or pen, with their eyes as it moves from side to side. A police officer will then look for certain involuntary jerking movements of the eye that indicate the driver has high levels of alcohol or drugs in their system.

How does the HGN Test work?

When someone is intoxicated, their eye movements can become uncoordinated, leading to involuntary jerking of the eyes. These movements are known as nystagmus. When performing the HGN test, a police officer will look for the following three signs of nystagmus:

  • The lack of smooth pursuit when the eye follows the object
  • The nystagmus is distinct when the eye is at maximum deviation (i.e., the eye moves to one side and is held there)
  • The angle of onset of nystagmus is within 45 degrees of center of the eye

How Reliable is the HGN Test?

While the HGN test is a widely used tool in detecting DUI, its reliability is often contested. Although the HGN test is based on science, it is subjective and relies heavily on the officer’s interpretation of the results. Moreover, several factors can affect the outcome of the HGN test, including:

  • Weather conditions (wind, rain, etc.)
  • Lighting conditions (e.g., flashing lights from a patrol car)
  • Medical conditions (e.g., glaucoma, head injury, ear disorders)
  • Prescription drugs
  • Illicit drugs
  • Alcohol consumption

Your Rights and the HGN Test

It is important to be aware of your rights concerning the HGN test. In some states, taking the HGN test is not mandatory, and refusing to take the test cannot be used against you in court. However, if you are suspected of DUI, refusing a blood, breath, or urine test can have severe consequences, such as losing your driving license or facing penalties, depending on where you live.

What Happens if You Fail the HGN Test?

If you fail the HGN test, the officer may arrest you on suspicion of DUI. However, the HGN test is just one piece of evidence that the officer will use to determine whether or not you are intoxicated. You may be asked to take other field sobriety tests, such as the walk-and-turn test or the one-leg-stand test. If you refused to take the HGN test or the officer believes that you are still under the influence of alcohol or drugs, you may be required to take a chemical test, such as a blood, breath, or urine test.

How to Fight HGN Test Results in DUI Cases

If you are charged with DUI based on the results of the HGN test, you can challenge the results of the test in court with the help of a DUI defense attorney. Several factors can affect the results of the HGN test, including the officer who conducted the test, the equipment used, and environmental factors. A skilled DUI defense attorney like Arja Shah can help ensure that the test results are fair and accurate.


In conclusion, the HGN test is an instrumental tool for determining whether a person is driving under the influence of drugs or alcohol. However, the test's reliability is often contested due to its subjectivity and its vulnerability to external factors. As someone charged with DUI based on the results of the HGN test, knowing your rights and working with a skilled attorney can help ensure that your case is treated fairly and accurately.

Horizontal Gaze Nystagmus Test in DUI Field Sobriety-Arja Shah, Esq., DUI Defense Attorney