What to Know About the Horizontal Gaze Nystagmus Test in Utah

When someone is suspected of drunk driving in Utah, the police typically conduct a series of Standardized Field Sobriety Tests to evaluate whether the driver is under the influence of alcohol. These tests are used to establish probable cause to believe a driver is intoxicated, which can lead to the driver being arrested and charged with Driving Under the Influence (DUI). One of the most common is the Horizontal Gaze Nystagmus test, also known as the “follow the pen” test or the “DUI eye test.”

While police and prosecutors want you to believe the Horizontal Gaze Nystagmus test accurately indicates whether a driver has had too much to drink, the test results can be inaccurate. Our experienced DUI defense attorneys can evaluate how police conducted the tests and work to have your performance on the tests excluded from consideration, which can lead to favorable plea negotiations.

What is the Horizontal Gaze Nystagmus Test?

“Nystagmus” refers to an involuntary jerking of the eye. The condition naturally occurs when someone looks to the side at an extreme angle, but alcohol, as well as certain drugs and medical conditions, can exaggerate the effect. Police use the Horizontal Gaze Nystagmus (or HGN) test to assess whether a driver might be under the influence of alcohol.

When conducting the test, the officer moves an object, often a pen, from side to in front of the suspect’s face while the suspect keeps their head still. When conducting the test, the officer is looking for “clues” that could indicate the driver is under the influence of alcohol. (The HGN test has not been approved to evaluate whether a suspect is under the influence of drugs.) Signs that a suspect is under the influence of alcohol include:

• Inability to move the eyes smoothly as they follow the object’s movement
• Inability to focus on the object and “jerking” of the eyes as they move to the extreme range of peripheral vision
• The onset of “jerking” before the eyes have reached a 45-degree angle

The officer assesses each eye for the presence of these characteristics, with one point awarded for each, up to a maximum of six points. A score of four points or more indicates a strong probability that the driver is impaired by alcohol.

How Accurate Is the DUI Eye Test?

The National Highway Traffic Safety Administration (NHTSA) has endorsed the Horizontal Gaze Nystagmus test as one of three standardized Field Sobriety Tests that can be used to assess whether a driver is under the influence of alcohol. While the test is based on science and police and prosecutors want the public to believe the test is highly accurate, there are several problems with its accuracy. Officers routinely administer the test incorrectly, holding the object too close to the suspect, moving it too quickly, or conducting the test under poor lighting conditions, all of which can affect the accuracy of the test results.

Medical conditions can also affect the accuracy of the test. For example, the HGN test is not accurate for individuals who only have vision in one eye, have a “lazy eye,” or are colorblind. A small percentage of the population (3% to 4%) naturally exhibits a pathological nystagmus, which could be caused by a neurological disorder, brain damage, or epilepsy. Similarly, a suspect who sustained a concussion may also exhibit nystagmus, rendering the test inconclusive. Fatigue and prescription medications can also cause nystagmus, while flashing lights, moving vehicles, or windy testing conditions can all make the nystagmus appear worse than it actually is.

Do I Have to Take the DUI Eye Test?

While Utah's implied consent laws require that drivers submit to chemical testing after a lawful arrest, field sobriety tests, including the DUI eye test, are voluntary.

Challenging the Results of the DUI Eye Test

While horizontal gaze nystagmus is a “clue” to intoxication, the results of the DUI eye test are far from conclusive. Our experienced DUI defense attorneys do not accept these test results at face value and can point out flaws in how the test was conducted, question the officer’s training, and identify other factors that may have affected the results.

Common strategies to challenge the results of the DUI eye test include:

• Questioning the officer’s training and whether they followed NHTSA guidelines
• Identifying alternative causes of nystagmus, such as a medical or eye condition
• Challenging the testing conditions, such as headlights from the police car or passing vehicles, or wind that might make the test results inaccurate
• Identifying conflicting evidence, such as whether the suspect’s speech, coordination, and behavior were normal

Our attorneys will identify problems with the testing process and flaws in the officer’s testimony to try to have the test results excluded. Even if the results of the DUI eye test are admitted, juries often find the results less persuasive once they understand its shortcomings and how the test results can be misinterpreted.

Contact the Experienced DUI Defense Attorneys at Douglas D. Terry & Associates Today

Douglas D. Terry & Associates is the longest-serving criminal defense firm in St. George and has been representing individuals charged with DUI and other crimes in Southern Utah since 1983. We offer the time-tested advice, guidance, and advocacy that only an experienced law firm can provide. Contact our office to schedule a confidential appointment to discuss your situation and how we can assist you. Call (435) 628-4411, send a message to email@SouthernUtahDefense.com, or complete our online form.