Most drivers in Missouri who have been arrested for DUI have undergone a field sobriety test. One of the three components to determine field sobriety is a procedure called an HGN test. HGN is an acronym for horizontal gaze nystagmus, a test that helps determine whether someone is under the influence of alcohol or drugs.
What the HGN test measures
Nystagmus is an involuntary bouncing or movement of the eyes. HGN refers to sideways eye movement, which can become more pronounced in individuals suspected of DUI. Those who exhibit HGN aren’t even aware of it because alcohol and some drugs can suppress the nervous system and because sideways eye movement doesn’t have an effect on vision. The HGN portion of the field sobriety test, which also includes the one-leg stand and walk-and-turn tests, is generally considered to be the most accurate portion of the field sobriety test.
During an HGN test, a police offer will tell you that your eyes are being checked as the officer asks you to follow an object, usually a lighted pen, with only your eyes. The officer will perform three distinct movements to watch how your eyes respond, which helps them determine whether you have been driving while impaired.
The problem with HGN tests
Law enforcement personnel must perform all field sobriety tests, including the HGN test, according to Standardized Field Sobriety Test Guidelines. You could possibly have a DUI charge thrown out if a judge determines that the test wasn’t properly conducted. Another complication involves the fact that nystagmus can be caused by the movement of inner ear fluid, eye strain, neural activity or even minor brain damage.
If you have a DUI case that hinges on an HGN test, you may want to consult with an attorney. A legal professional may explain the test’s limitations in court in an attempt to get you cleared of the charges.