What to Know About the Horizontal Gaze Nystagmus Test in Washington

When you’re pulled over for suspected drunk driving in Washington, one of the first things an officer might ask you to do is follow a pen or flashlight with your eyes. This is called the Horizontal Gaze Nystagmus (HGN) test—a standard part of field sobriety testing. While it might seem simple, this small eye movement test plays a big role in DUI cases.

What Is the Horizontal Gaze Nystagmus Test

Nystagmus is an involuntary jerking or twitching of the eyes. It naturally occurs when someone looks to the side at extreme angles, but alcohol and certain drugs can exaggerate the motion. The HGN test is designed to detect these exaggerated jerks as a possible indicator of impairment.

During the test, the officer moves an object—often a pen or small light—side to side while you keep your head still and follow it with your eyes. The officer looks for three key signs in each eye:

• Whether your eyes move smoothly as they track the object
• Whether distinct jerking begins before your eyes reach a 45-degree angle
• Whether the jerking continues when your eyes are all the way to the side

Each clue can add to the officer’s suspicion that you’re impaired. If the officer sees enough signs, they may use that observation—along with other factors—to justify an arrest or a chemical test.

The Science and Limitations Behind the HGN Test

On paper, the HGN test is based on science. The National Highway Traffic Safety Administration (NHTSA) recognizes it as one of three standardized field sobriety tests, along with the walk-and-turn and the one-leg stand. But in practice, several problems can affect its accuracy. Officers often administer the test incorrectly or interpret the results inconsistently. Even small errors—like holding the stimulus too close, moving it too fast, or testing under poor lighting—can skew the results.

Medical and environmental factors also play a major role. Fatigue, certain eye conditions, neurological disorders, and even prescription medications can cause nystagmus. Flashing lights, moving vehicles, or wind in your eyes can all make the jerking appear worse than it actually is. This is why your defense attorney will scrutinize how the test was conducted. If the officer didn’t follow NHTSA standards precisely, the results may not be reliable enough to use against you.

How Washington Courts Treat the HGN Test

In Washington, prosecutors can use HGN test results as evidence in DUI cases, but only under certain conditions. Courts expect the state to show that the officer was properly trained, the test was performed correctly, and the observations were scientifically valid. However, Washington courts have drawn lines on how far the state can go. Officers can describe what they observed—such as visible eye jerking—but they can’t claim those movements directly prove your exact blood alcohol content.

The HGN test usually serves as one piece of the puzzle, not the entire picture. When combined with other observations—like driving behavior, speech patterns, or breath test results—the prosecution may argue it supports a DUI charge. But a skilled defense lawyer can challenge whether the officer had enough grounds to use it in the first place or whether it was performed in a valid way.

Defending Against HGN Test Results

A strong DUI defense doesn’t accept field sobriety test results at face value. Your lawyer can look for flaws in how the HGN test was administered, question the officer’s training, and identify any factors that might have influenced the results.

Common defense strategies include:

• Questioning the officer’s procedure: If the officer didn’t follow standardized NHTSA guidelines, the test loses credibility.
• Identifying medical or visual conditions: Eye disorders, head injuries, or even contact lenses can cause false signs of nystagmus.
• Challenging the testing environment: Headlights, patrol car lights, or uneven terrain can all affect how your eyes respond.
• Pointing out conflicting evidence: If your speech, coordination, and behavior were normal, that may undercut the officer’s claim of impairment.

Your attorney can also cross-examine the arresting officer to expose inconsistencies or lack of training. These details can determine whether the evidence is admissible or whether it should be excluded from trial. Even if the HGN test is allowed, juries often find it less persuasive once they understand how easily it can be misinterpreted. The more your defense highlights its limitations, the weaker it becomes as proof of guilt.

What Happens if You Refuse or Fail the Test

Washington’s implied consent laws require drivers to comply with lawful requests for breathtesting after arrest, but field sobriety tests like the HGN are voluntary. You’re not legally required to perform them, and refusing won’t lead to administrative license suspension the way refusing a breath test would.

Still, refusing can carry practical consequences. The officer may use your refusal as a factor in deciding to arrest you, and prosecutors might argue that it shows consciousness of guilt. On the other hand, submitting to an improperly conducted test can give the state more evidence to use against you. If you did take the test and failed, don’t panic. The HGN test is just one component of a larger case, and your attorney has several ways to challenge it.

Protecting Your Rights After a DUI Stop

Field sobriety tests, especially the Horizontal Gaze Nystagmus test, often sound more scientific than they really are. In reality, they’re subjective tools that depend heavily on an officer’s training, experience, and environment. For many people, that means the test can produce misleading results.

If you were arrested for DUI in Washington after taking or refusing an HGN test, it’s important to get help immediately. The sooner you talk to a lawyer, the better your chances of preserving your license and building a strong defense. Talk to Fox Law Firm today. Our team understands the science and the strategy behind DUI defense in Washington. We’ll review every detail of your stop, the officer’s actions, and the evidence against you. Your rights and your future deserve a fair defense—let’s start building it now.