Horizontal Gaze Nystagmus Defense Lawyer in CA

If you were arrested for DUI in Sacramento, there is a very good chance that the police officer who arrested you did something called a Horizontal Gaze Nystagmus (HGN) test. Most people haven't heard the phrase, but they actually do know what it is if they are familiar with field sobriety tests.

When law enforcement officers pull someone over, and they suspect alcohol impairment, they may ask to do field sobriety tests. These include tests like the one-leg stand test and the walk-and-turn test. Additionally, they will do the HGN test before determining if other tests, like breath tests or blood tests, are appropriate. The officer conducting the test might also do non-standardized tests, like asking you to say the alphabet backwards or noticing slurred speech, to determine a possible need for field sobriety tests, too.

It's important to realize that if you have failed the HGN test, there are ways to challenge the results. Goss Law is a California DUI law firm that works with people who are facing DUI convictions. They can also review causes of false positives on a breathalyzer test. Understanding what it is and how it works is important in building a case. Also, working with the right horizontal gaze nystagmus defense lawyer in CA can really make or break your case.

What Is the Horizontal Gaze Nystagmus Test as Part of Field Sobriety Tests

The horizontal gaze nystagmus test is one of the standardized field sobriety tests approved by the National Highway Traffic Safety Administration (NHTSA). It is meant to detect involuntary jerking of the eyes, which is said to be an accurate indication that someone has consumed alcohol.

During the test, the police officer or California Highway Patrol officer will as you to follow a small object, like a pen or flashlight, or even the officer's finger, with your eyes while not moving your head. They will look for specific "clues" in each eye:

1. Lack of smooth pursuit

2. Distinct and sustained nystagmus at maximum deviation

3. Onset of nystagmus prior to 45 degrees

If the officer sees poor performance in the test, they may conclude that you are intoxicated. If that's they case, they can arrest you.

Here's the caveat though -- this is not a chemical test. It doesn't measure your blood alcohol content, nor does it technically prove alcohol consumption. Instead, it's a subjective test done at a traffic stop where external factors, like headlights in a driver's eyes, hard contact lenses, or even a previous head injury, could also cause these "three clues" to appear.

Because of this, it's always a good idea to work with an experienced criminal defense attorney in any DUI case. For more information, these criminal defense law firms in Sacramento may be able to help.

Why the HGN Test Is Often Challenged for California DUI Charges

Courts do allow the prosecution's case to include HGN evidence, but only when it is done correctly and within its scientific limits. An experienced attorney will look at facts like if the officer complied with NHTSA standards or whether other factors could have caused the eye movements.

Improper Administration

In order for the test to be somewhat accurate, the officer must position the stimulus (pen, finger, flashlight) correctly. It must move at a certain speed, and be held at maximum deviation for a specific amount of time. If the test is rushed, done in poor lighting, or the officer doesn't give proper instructions, the results can be unreliable.

Oftentimes, body camera footage is used to prove if the officer moves too quickly or if the officer holds the stimulus in the wrong place.

Medical and Environmental Factors

Nystagmus, or movement, can occur for a number of reasons that are unrelated to alcohol consumption. These include:

• Fatigue

• Inner ear disorders

• Certain medications

• Neurological conditions or issues with the central nervous system

• Flashing lights (such as police emergency lights or headlights)

If you were tested on the side of the road at night with patrol lights flashing in your peripheral vision, that environment alone can affect eye movement.

Officer Qualification

Not every officer is equally trained in administering HGN tests. Defense attorneys frequently review training records to determine whether the officer completed proper certification or refresher training.

If qualifications are lacking, the prosecution may struggle to establish the scientific reliability of the results.

How Prosecutors Use HGN Evidence

In many Sacramento DUI cases, HGN is used to:

• Establish probable cause for arrest

• Support officer testimony about impairment

• Strengthen the case when chemical test results are close to the legal limit

Under California Vehicle Code § 23152, it is illegal to drive under the influence of alcohol or drugs, and separately illegal to drive with a blood alcohol concentration of 0.08% or higher. Even if a chemical test result is marginal, prosecutors may rely on field sobriety tests like HGN to argue impairment.

That’s why challenging field sobriety evidence can be critical to your defense.

The Science Behind Nystagmus — and Its Limits

Nystagmus is a real physiological phenomenon. Alcohol can exaggerate it. However, the leap from “eye jerking observed” to “driver was legally impaired” is not as straightforward as officers sometimes suggest.

The HGN test does not provide a specific BAC reading. It does not prove impairment on its own. It is intended to be one observational tool among many.

A skilled defense lawyer may consult expert witnesses who can explain:

• How alcohol affects eye movement

• How other conditions can produce similar signs

• Why roadside conditions reduce reliability

• The difference between laboratory studies and field administration

In some cases, expert testimony can significantly weaken the prosecution’s reliance on HGN evidence.

Suppression and Evidentiary Motions

An experienced Horizontal Gaze Nystagmus defense lawyer in California will not simply accept the officer’s conclusions at face value. Instead, your attorney may:

• File motions to suppress improperly obtained evidence

• Challenge foundation for admission of HGN testimony

• Cross-examine the officer about deviations from protocol

• Question the scientific interpretation offered in court

If the officer lacked probable cause before the arrest — and relied improperly on HGN — the entire case may be vulnerable to challenge.

Why Local Representation in Sacramento Matters

DUI cases are prosecuted locally, and procedures can vary by jurisdiction. Having counsel familiar with Sacramento courts, prosecutors, and judges can make a significant difference in strategy.

The Sacramento County Superior Court handles DUI matters arising in the area. Local practice knowledge — including how individual judges treat HGN-related objections — is valuable when building a defense.

At Goss Law, we analyze every DUI case with attention to technical detail. Field sobriety tests are not automatically accepted as accurate. They are scrutinized carefully.

What You Should Do After a DUI Arrest Involving HGN

If you were subjected to a Horizontal Gaze Nystagmus test, take these steps immediately:

1. Write down everything you remember about the stop.

2. Note lighting conditions, surface conditions, and patrol vehicle positioning.

3. Recall whether flashing lights were in your line of sight.

4. Document any medical conditions or medications.

5. Contact a DUI defense attorney promptly.

Time matters. In California, you have a limited window to request a DMV hearing after a DUI arrest. Protecting your driving privileges requires fast action.

Work with a DUI Defense Attorney - Reach Out to Goss Law

The Horizontal Gaze Nystagmus test is often portrayed as scientific and objective. In reality, it is a roadside assessment that depends heavily on proper administration, environmental control, and officer interpretation.

When used correctly, it may be one piece of evidence. When used improperly, it can unfairly strengthen a weak DUI case.

If you’re facing DUI charges in Sacramento and HGN was part of your arrest, you should not assume the evidence is unbeatable. A knowledgeable defense attorney can examine the details, identify weaknesses, and build a strategic response tailored to your case.

At Goss Law, the team approaches every DUI case with precision and a deep understanding of California law. If you need a Horizontal Gaze Nystagmus defense lawyer in California, taking action early can make all the difference in protecting your license, your record, and your future. Reach out for a free consultation.