What is the horizontal gaze nystagmus test?
The horizontal gaze nystagmus (HGN) test is one of the three field sobriety tests developed by the National Highway Traffic Safety Administration. It is a test to help law enforcement determine if a driver is impaired by alcohol and is routinely used in DUI investigations.
Here is a question we received regarding HGN:
Question:
I live in Lawrenceville, Georgia, and I got arrested for DUI in Duluth, Georgia, where I work. I came from a local bar where I was hanging out with some coworkers, and I think the cop saw me swerve when I looked at the GPS on my phone, and then he pulled me over, almost like he was watching the bar.
I was mostly cooperative, and the police officer spent a lot of time looking at my eyes and I don’t know why. Can the cop really tell if I’m drunk by looking at my eyes? I have a court date at the Gwinnett County Recorder’s Court and I need help.
T.R., in Gwinnett County
Answer:
As Georgia DUI lawyers we are frequently asked about the horizontal gaze nystagmus test, known as HGN, that the police officer performed on you. It’s part of the so-called field sobriety tests law enforcement utilizes when making a DUI arrest.
Horizontal gaze nystagmus (HGN) is frequently used as one of the three major standardized field sobriety tests (SFSTs) by law enforcement officers to detect impairment due to alcohol or drugs, including during DUI (Driving Under the Influence) stops.
Here's how HGN relates to DUI cases:
HGN Test during DUI Stops:
- Field Sobriety Testing: During a DUI stop, an officer may administer standardized field sobriety tests to assess the driver's level of impairment. Most of the time an officer will do so, but not always -- for instance, if there was an accident involved a cop may skip the HGN and other tests.
- HGN Test Procedure: The HGN test involves observing the eyes of the individual as they track a stimulus (such as a pen or fingertip) moving horizontally from side to side. The officer looks for involuntary jerking of the eyes (nystagmus) as they move. The onset of nystagmus prior to a 45-degree angle is one indicator of impairment. Police officers are usually not medically trained, so their skill administering the test varies quite a lot.
- Indicator of Impairment: The presence of HGN, especially at specific angles, is often considered an indication of impairment due to alcohol or certain drugs. However, it's important to note that HGN alone does not confirm intoxication but rather suggests the possibility of impairment.
Limitations and Considerations:
- Accuracy: While HGN testing can indicate alcohol or drug impairment, it's hardly foolproof and can be affected by various factors including lighting conditions, medical conditions, and the officer's training and interpretation.
- Corroboration: HGN is typically used in conjunction with other field sobriety tests and observations to build a case for impairment.
- Legal Challenges: Defense attorneys may challenge the validity of HGN testing procedures or the officer's interpretation of the results in court.
- Subjectivity: The interpretation of HGN is very subjective and relies on the officer's training and experience, which can vary.
- Medical Conditions: Certain medical conditions or medications can also cause nystagmus (including inner ear disorders, head injury, stroke, Lyme disease and brain tumors), which may not be related to alcohol or drug impairment.
Legal Implications:
If an individual fails the HGN test and is subsequently arrested for DUI, the results of the HGN test can be used as evidence in court. However, the admissibility and weight given to this evidence may vary based on legal standards and the circumstances of the case.
In summary, while HGN testing is commonly used in DUI investigations, its interpretation and reliability can be subject to debate, and it's just one piece of evidence in determining impairment and establishing guilt in DUI cases.
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