DUI defense attorneys have challenged the HGN test (Horizontal Gaze Nystagmus test) for years. The HGN test is a field sobriety test traditionally used by police to determine whether a driver may be under the influence of alcohol.

To administer the test, officers ask the subject to follow a finger or pen with their eyes without moving their head. The officer looks for nystagmus—an involuntary, rapid, rhythmic movement of the eyeball. Critics argue that the test is unreliable because nystagmus can have many causes, and the test is often administered incorrectly.

Previously, an Illinois appellate court ruled that HGN test results were inadmissible at trial, a major victory for DUI defense attorneys. However, the Illinois Supreme Court recently addressed this issue and held that the HGN test is generally accepted in the scientific community as evidence of alcohol consumption and possible impairment. Therefore, it may now be admissible at trial.

Prosecutors welcomed this decision, but a closer review of the Court’s opinion shows that defense attorneys may still find significant advantages.

Key Takeaways from the Supreme Court’s Opinion

• The HGN test does not prove actual impairment, only possible impairment.
• Failing the HGN test correlates only to a blood alcohol content (BAC) of .04–.06%.
• There are at least 125 causes of nystagmus unrelated to alcohol.
• The HGN test cannot be used to suggest a BAC above .08%.
• Admissibility depends on strict compliance with National Highway Traffic Safety Administration (NHTSA) guidelines. Illinois officers, however, receive only a 6-hour course rather than the full 24-hour NHTSA training.
• Expert testimony revealed that only 1 in 100 officers can perform the test correctly.

What This Means Going Forward

While it is unfortunate that the Illinois Supreme Court deemed the HGN test admissible, the ruling substantially limits its value in DUI prosecutions. Trial courts will now have to decide how to handle the test under these new restrictions. For DUI defense attorneys, the ruling still leaves significant room to challenge the accuracy and reliability of the HGN test in court.

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