What does the "Eye Test" tell Police Officers Investigating a DUI?

What is the “eye test”?

The so-called “eye-test”, as it is commonly called, is one of the most common field-sobriety tests employed by law enforcement officers during a DUI or DUII stop. Otherwise known as the Horizontal Gaze Nystagmus (HGN), it is performed by an officer moving an object like a pen or finger back in forth in front of a person’s eyes and the results can tell an officer if alcohol is present in your body.

In this post, I’ll talk about how the eye test is conducted, discuss the accuracy of the eye test, and help you understand your rights when it comes to field sobriety tests in Oregon.

What does an officer look for during an eye test?

Whether you’re under the influence of alcohol or not, your eyeball is always making tiny imperceptible twitches. They’re involuntary, meaning you can’t control them. Imagine a cork floating in a glass of water. It’s not sitting completely still even though it might not look like it’s moving.

These rapid involuntary eye movements are known as nystagmus-- that’s the “N” in the HGN test. Under normal circumstances it takes a doctor using a special medical instrument to spot these movements.

Now imagine stirring the glass of water. The cork’s movements will become much more obvious. Similarly, when under the influence of alcohol, tiny involuntary eye movements become more pronounced and visible to someone who knows what to look for-- like a properly trained police officer.

As an object is moved in front of your eyes, across your field of vision, the officer will look for a  visible twitch or quiver in your eyes as they follow the object, especially near the peripheral edges of your vision. If present, these movements show alcohol is present in your system. If you are sober, the twitches or quivers, will remain invisible to the naked eye.

Is the eye test accurate?

The HGN test is one of three accepted field sobriety tests (FSTs) along with the Walk-and-Turn (WAT) and One-Leg-Stand (OLS) tests. A properly administered HGN test can help an officer make a better determination as to whether you are under the influence of alcohol. Unlike some other tests, there is scientific evidence validating the HGN.

The key is proper administration. All field-sobriety tests have their drawbacks, which are magnified when not properly administered. The results of an HGN test can be affected if:

  • You are wearing glasses. An officer may misinterpret the results of the HGN test if he or she can’t see your eyes clearly.

  • You are facing traffic or a squad car’s flashing lights. Bright, moving or blinking lights, can cause what is known as an optokinetic nystagmus, which can lead to a false-positive result for an HGN test.

  • Your eyes are twitching for another reason. The Mayo Clinic reports there are over 40 possible reasons why a person’s eye may twitch, including stress, multiple sclerosis, Bell’s palsy, and caffeine intake, among many others.

Overall, some scientific studies have found that even under ideal conditions an HGN test is only about 80% accurate. In other words, roughly 1 out of 5 people who are deemed impaired by an HGN test will actually not be impaired. Those aren’t great odds. Other field sobriety tests are even worse, with false positives happening as much as 33% of the time.

Am I required to consent to an HGN test?

As noted above, the HGN test is one of three commonly used field sobriety tests an officer can use to establish probable cause to make an arrest for DUI. In the state of Oregon, court decisions have determined field sobriety tests are “searches” which require consent before they may be administered.

Let me be clear: You always have the right to refuse an HGN test or another field sobriety test.

An officer will do everything in his or her power to convince you to perform an FST, but they can’t make you do it, and unlike Oregon’s Implied Consent laws (which I’ll get to in a second), there is no penalty for refusing a field sobriety test.

You should be aware that an officer will often use something called “Rohr’s admonishment” to convince you to take part in a field sobriety test, like an HGN test. He or she will say your refusal to consent to an FST will be used as evidence against you at trial--it will show you have a “guilty mind.”

Any competent attorney will tell you this can be easily overcome should you end up at trial. A person doesn’t owe the police anything and refusing to be searched is only evidence that you know and protect your own Constitutional rights.

What will happen if I refuse to take an HGN test?

It is possible you may still be arrested for DUII based on the officer’s personal observations. However, by refusing to perform Field Sobriety Tests, you have denied the officer much of the evidence he would need you prove your guilt if you fought the charges at trial.

Remember though, the Implied Consent laws do impose a penalty for refusing to give a breath, blood, or urine sample. Even after you refuse the officer could obtain a warrant to take your blood without your consent.

The bottom line is, because you don’t have to perform field sobriety tests, and there is no real penalty if you don’t, it almost always makes more sense to simply and politely refuse.  

Have you been arrested for DUI or DUII in Oregon?

Have you been arrested and charged with DUI or DUII in Oregon? Do you have questions about whether your sobriety test was performed correctly?

If so, contact me or call (503) 227-3800 for a free, confidential consultation. I can help.

Photo Credits: Sam Bald, Oregon Department of Transportation