HGN Test: What It Is and Clues Officers Look For

Being pulled over for a suspected DUI is scary. Even more unsettling is when you’re put through a series of impairment tests that you’re unprepared for—what you see in the movies is not always how it happens in real life.

Because a DUI has such serious consequences that can impact one's personal and professional life, it's crucial to understand what will likely happen during a traffic stop and be armed with knowledge about what the police officers will be looking for. To that end, the HGN test is one of the most common tools used by officers to detect impairment.

What Is the HGN Test?

The HGN test, or horizontal gaze nystagmus test, is a part of the standard field sobriety test (SFST) used by law enforcement to help determine whether a person is impaired by alcohol or certain other drugs. Nystagmus is a condition where the eyes involuntarily jerk or wiggle, and it becomes more pronounced when a person is impaired by alcohol or illicit and prescription drugs, among other things.

The HGN test is one of three approved SFSTs that have been approved by the The National Highway Traffic Safety Administration (NHTSA). The other two approved SFSTs are the Walk and Turn and the One-Leg Stand. The NHTSA has specific guidelines on how police officers should administer each SFST and states that these particular tests were chosen because “...scientifically validated clues of alcohol impairment have been identified for each of these three tests. They are the only standardized field sobriety tests for which validated clues have been identified.”

HGN Test: Clues Indicating Impairment

During the HGN test, an officer will observe the eyes of a person as they follow a slowly moving object—usually the tip of a pen or small flashlight—horizontally with their eyes. The officer looks for three indicators of impairment:

1. Lack of Smooth Pursuit: The eyes can't follow a moving object smoothly.
2. Distinct Nystagmus at Maximum Deviation: Nystagmus becomes pronounced and sustained when the eye is looking as far to the side as possible.
3. Onset of Nystagmus Before 45 Degrees: The eye begins to jerk as it follows the moving object before it reaches a 45-degree angle from the center.

The officer is looking for these three clues in each eye, so a person could receive a total of six “points” of impairment. If four or more HGN test clues are evident between the two eyes, it suggests to the officer that the individual may be impaired.

What If You Fail an HGN Test?

While HGN testing can be a useful tool for detecting impairment, it’s not foolproof and results can be affected by various factors, including medical conditions, the environment, and officer training. In other words, the HGN test and other SFSTs are not pass/fail.

If you’ve been arrested for a DUI because you performed poorly on an SFST, contact an experienced attorney immediately. Your lawyer will determine if the correct procedures were followed, including whether:

• The officer had probable cause to pull you over (this is an essential justification for a traffic stop)
• The officer properly administered the HGN test (or other SFSTs)
• You have other conditions or factors, such as those taking certain medications, that could impact test results

If the officer determines that you did not perform the test(s) properly, you’ll be arrested for driving under the influence (DUI). If you are arrested for a DUI, Oklahoma law mandates that you must submit to a chemical test—such as a breathalyzer or blood test—within at least two hours of driving, which can further confirm your level of impairment.

If you’ve been arrested for a DUI, The Oklahoma DUI Guy can help. Our experienced attorneys will assess your case and work to get you the best possible outcome, limiting the impact of this situation on your life. Contact us today for a free case evaluation to see how we can help you.