The Truth Behind the DUI Eye Test: Outdated Science, Officer Mistakes, and Your Rights in Arizona

If you’ve ever been stopped for a DUI in Arizona, you know how fast things can escalate. Blue lights flash. Adrenaline kicks in. And suddenly, an officer is waving a pen in front of your face, asking you to follow it with your eyes.

This is what’s known as the HGN test—short for Horizontal Gaze Nystagmus. It’s one of the three “validated” field sobriety tests used across the country. But here’s the thing: validated doesn’t mean flawless. And it definitely doesn’t mean fair.

At Grand Canyon Law Group, we’ve defended countless clients charged with DUI, and we can tell you this: the HGN test is one of the most misunderstood and misused tools in DUI investigations. Let’s break down what it is, why it’s used, and why you should think twice before agreeing to take it.

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What Is the HGN Test?

The HGN test looks for nystagmus, or the involuntary jerking of the eyes. This jerking becomes more pronounced when a person has consumed alcohol—at least, that’s what the National Highway Traffic Safety Administration (NHTSA) claimed back in the 1990s.

During the test, the officer will hold a pen or finger about 12 to 15 inches in front of your face and slowly move it from side to side, watching your eyes for “clues” of impairment.

Specifically, the officer is looking for three indicators in each eye:

Lack of smooth pursuit – your eyes jerk instead of following the object smoothly.
Distinct nystagmus at maximum deviation – your eyes jerk when looking as far to the side as they can.
Onset of nystagmus before 45 degrees – your eyes begin to jerk before reaching a 45-degree angle.

If you show four or more clues across both eyes, you fail the test.

The Big Problem: Outdated and Inconsistent Science

Here’s the kicker—the validation studies used to support the HGN test date back to the 1970s and 1980s. The most often cited studies were published by NHTSA in 1998 or earlier, and many experts agree: science and standards have evolved since then. Field sobriety testing hasn’t.

That means today’s DUI investigations are relying on decades-old research and zero modern peer-reviewed studies validating how officers use the HGN test in the field. You wouldn’t trust a 25-year-old study to diagnose a health condition—why should it determine your guilt?

🔗 Read more on the NHTSA field sobriety testing studies here

Another Major Issue: Human Error

Let’s be honest—cops aren’t robots. They’re human, and humans make mistakes. Unfortunately, in DUI stops, even small mistakes during the HGN test can completely skew the results.

We’ve reviewed countless bodycam videos where officers:

Move the stimulus too fast (when it should take at least 4 seconds per pass)
Hold the pen too close or too far
Angle the object improperly, throwing off the test completely
Skip required instructions or don’t explain the test at all
Perform the test on people who medically or physically shouldn’t be tested at all

And yes—some people shouldn’t be given the test in the first place.

Who Shouldn’t Be Taking the HGN Test?

According to NHTSA’s own guidelines, the HGN test should not be used on:

Individuals over the age of 65
Anyone with inner ear disorders
People with neurological issues or eye conditions
Individuals who are significantly overweight
People wearing hard contact lenses
And—this one matters—anyone on uneven ground, in high winds, or poor weather

Yet we regularly see Arizona officers conducting the HGN test in:

Dirt fields
On the side of busy roads
In the rain
In direct sunlight
With sirens, traffic, and stress swirling around the scene

That’s not science. That’s guesswork dressed in a uniform.

The Bottom Line: It’s Not a Test You Can Pass

Let’s be real—these tests aren’t neutral evaluations. They’re evidence-gathering tools. Once an officer decides you might be impaired, the HGN test is often used to build a case against you, not give you a fair chance.

Unlike a blood or breath test (which is governed by strict rules), the HGN test is based on subjective observation. That means if an officer sees what they think is nystagmus, you’re probably getting arrested—even if the conditions made the test completely unreliable.

So, Should You Refuse the HGN Test?

Yes. Politely, but firmly.

You’re not legally required to participate in field sobriety tests—including the HGN test—in Arizona. While refusing a chemical test (like breath or blood) has serious consequences, refusing an HGN test does not.

If you’re stopped, say:

“I’d like to speak with an attorney before performing any tests.”

Then call Grand Canyon Law Group.

What If You Already Took the HGN Test?

If you already performed the HGN test, don’t panic. Many times, we can challenge it. As former prosecutors, we know the holes in these cases—and we know how to use them.

We dig into:

Officer training records
Body camera footage
Test administration protocols
Your health history and medical records

And we use that to attack the reliability of the test in court.

Need Help Fighting a DUI Charge in Arizona?

DUI charges are serious. They can impact your license, your career, and your future. But just because you were arrested doesn’t mean you’ll be convicted—especially if the case hinges on questionable field sobriety tests like the HGN.

At Grand Canyon Law Group, we fight to protect good people who’ve been accused of crimes. We bring years of experience as former prosecutors and exclusive focus on criminal defense in Arizona.