Understanding Horizontal Gaze Nystagmus Testing in a CA DWI

Driving while impaired, or DWI, is a very serious offense in California, and law enforcement officers will use a number of methods to determine if a driver is under the influence of alcohol or drugs. One of the most common tests that a police officer might use is called the Horizontal Gaze Nystagmus test, or HGN test.

For drivers here in Sacramento, or those for those across the state, understanding what these tests mean, what they involve, how it is done, and what it means for a DWI case is very important.

Working with a lawyer can help you with understanding horizontal gaze nystagmus testing in a CA DWI, too, which is why it's so important to have a DWI lawyer on your case as soon as possible. They can also explain how retrograde extrapolation is used in DWI cases in CA.

What Is Horizontal Gaze Nystagmus (HGN) in a DUI Case

Horizontal Gaze Nystagmus refers to the involuntary jerking, also called oscillation, of the eyes as they follow a moving option horizontally. In other words, when you look at something that is moving horizontally in front of your face, the eyes naturally begin to move side-to-side. However, when a person is intoxicated, the eyes behave differently, and they could look jerk around or move faster, etc.

Law enforcement agencies train their officers to observe these eye movements, and doing so can help to determine if the driver is impaired.

How the HGN Test Is Administered in DUI Investigations

When a person is pulled over during a traffic stop because the officer believes they are impaired, it's very common for them to do a series of Standardized field sobriety tests. HGN is one of these tests.

Typically, the HGN test is done in the following way:

1. First, the driver is asked to stand with their feet together and their hands at their side while they listen to the officer's instructions.

2. Next, the officer will hold a small object in front of the driver believed to be drunk driving. This might be a pen, a small flashlight, or even a finger. The officer conducting the test will hold the object 12-15 inches from the driver's eyes and slightly above eye level.

3. The driver is then asked to follow the object as the officer moves it, but only with their eyes. When doing the test, the officer will look at each eye and seek out specific signs of intoxication. First, they will look for "lack of smooth pursuit," which means the eye isn't following the object in a smooth manner. Next, they will look for distinct and sustained nystagmus at maximum deviation. This means that when the eye is moved horizontally as far as it will go, distinct nystagmus, or jerky movement, is noticeable. Finally, they will look to see if the nystagmus occurs before the eye reaches a 45-degree angle.

4. Once all of this is considered, officers will use a point system to determine the likelihood of having a BAC over the legal limit.

The HGN test is designed to be standardized, but the results can be subjective, and officers must follow precise procedures for the test to be legally reliable.

Why HGN Testing Is Used in California

The HGN test is an important part of California's DUI enforcement plan for a number of reasons:

First, it is an objective indicator of impairment. Unlike a subjective observation, HGN offers an involuntary movement of the body that is commonly associated with impairment.

Officers can also use the HGN test as evidence for probable cause. This means that they can legally arrest a person who fails the HGN test.

Finally, it can be used as solid court evidence against the driver. It is often supported by other test results including breath tests and blood tests.

One thing is important to mention -- HGN can and does indicate that a person is under the influence of alcohol, but is cannot measure BAC directly. There are a number of medical disorders, medications, and other things, like fatigue, which can also cause the same movements.

Accuracy and Limitations of the HGN Test

It's true that the HGN test is considered to be a more accurate field sobriety test, but it does not mean that the person is always impaired. As mentioned, there are several factors that can affect the test and its reliability.

First, there are medical conditions like inner ear disorders, head injury, neurological disorders, or certain drugs prescribed by doctors that can cause the eyes to do the same thing. Even contact lenses can cause natural nystagmus.

Next, there is the possibility that the test wasn't done correctly. It is only admissible if proper administration was done during the DUI arrest.

Environmental factors might also come into play. For instance, poor lighting, distractions, or uneven surfaces can interfere with the driver's ability to do the test correctly.

Finally, even though officers are trained to do the test, and even if it was properly administered, involuntary jerking of the eye is still partially subjective, which means it can be a point of contention in court.

HGN Test Results and Their Legal Implications

In California, the results of an HGN test are often used alongside other field sobriety tests, driver behavior observations, and chemical tests to build a DUI case. Key considerations include:

• Probable Cause for Arrest Observing multiple signs during the HGN test can provide law enforcement with probable cause to arrest a driver for DUI.

• Evidence in Court Prosecutors may present HGN results to support claims of impairment, even if breath or blood tests are inconclusive.

• Defense Strategies Defense attorneys can challenge the validity of HGN evidence by questioning the officer’s training, the test administration, or alternative explanations for eye movements.

Understanding the role of HGN in your case can be critical to mounting a strong defense and potentially reducing or dismissing charges.

Other Standardized Field Sobriety Tests

HGN is often administered with additional tests as part of California’s Standardized Field Sobriety Tests:

1. Walk-and-Turn Test Drivers are instructed to walk in a straight line, heel-to-toe, turn, and return. Difficulty following instructions may indicate impairment.

2. One-Leg Stand Test Drivers are asked to balance on one leg while counting aloud. Swaying, hopping, or putting the foot down may suggest impairment.

3. Additional Observations Officers may also note slurred speech, the smell of alcohol, or erratic driving behavior.

Each test lends to establishing probable cause and may be scrutinized by an experienced DUI defense attorney. The sooner you employ a DUI attorney for your case, the better off you will be. They can advise you from the moment you pick up the phone.

Defense Strategies Against HGN Evidence

An experienced attorney can work with a person charged with drunk driving and come up with a number of different defense strategies specifically when considering HGN evidence.

First, they can question the officer's training. HGN results can be inadmissible to the court if the officer was not properly trained to do this type of field sobriety test.

It's also possible to argue that the test results are inaccurate because the test was administered incorrectly. If there is even a slight deviation from the standard procedure, such as improper position or timing, it's very possible to challenge the results in court.

As mentioned, if the person charged with a DWI has medical conditions or other physiological issues that might affect the eye's movement, this can be a defense, too. Things like prescription medications, issues with the central nervous system, or even wearing contact lenses can affect how the eyes move.

Finally, it can also be argued that environmental factors affected the outcome of the test. Poor lighting, too much wind, or standing on an uneven surface can affect the driver's ability to do the HGN test accurately.

By taking a closer look at all of these factors, a drunk driving lawyer can potentially argue in defense of their client and get a more positive outcome. Remember, the prosecution has to prove, beyond a reasonable doubt, that the driver was intoxicated. But a defense attorney can introduce doubt in a number of different ways.

Facing DUI Charges? Contact Goss Law for a Free Consultation

The Horizontal Gaze Nystagmus test is a powerful component of California’s DUI enforcement, but it is not infallible. Understanding how the test works, its limitations, and how it can affect your DWI case is essential for anyone facing DUI charges in Sacramento or across California.

If you have been arrested for a suspected DWI and HGN testing was involved, consulting a knowledgeable attorney such as Goss Law can make a significant difference in the outcome. From challenging improper test administration to evaluating medical explanations for involuntary eye movements, a skilled defense strategy can help protect your rights, your license, and your future.

Contact Goss Law today to discuss your case and learn how experienced legal representation can help you navigate the complexities of DUI law in California. Free consultations are available.