The horizontal gaze nystagmus (HGN) test is a key component of the standardized field sobriety test used by law enforcement to assess a person’s level of impairment due to alcohol.
The HGN test evaluates the involuntary jerking of the eyes, which becomes more pronounced when a person is under the influence of alcohol. Understanding how this test works can help individuals who are facing drunk driving charges that include this test as part of the evidence against them.
Administration of the test
During the test, an officer will ask the individual to follow a small object, such as a pen or a light, with their eyes. The officer moves the object horizontally in front of the person’s face, watching for three specific clues in each eye: lack of smooth movement, distinct and sustained nystagmus at maximum deviation and the onset of nystagmus before the eyes reach 45 degrees.
Reliability of the test
The HGN test is generally considered reliable and is endorsed by the National Highway Traffic Safety Administration as part of the standardized field sobriety test. However, it isn’t infallible. Certain medical conditions, neurological disorders and even some medications can cause nystagmus, potentially leading to false positives. Additionally, improper administration of the test can affect its accuracy.
The administration methods and interpretation of the results can sometimes come into the picture as part of a defense strategy. Discussing this matter with someone familiar with these cases can help defendants to determine how to proceed.