The horizontal gaze nystagmus test (HGN) is a type of field sobriety test used by Georgia law enforcement officers to detect impairment due to alcohol or drugs. The test involves observing a person’s eye movements as they track an object moving horizontally.
How the test works
During the test, the officer will ask the person to follow a moving object, such as a pen or a finger, with their eyes. The object is moved horizontally across the person’s field of vision, and the officer observes the person’s eye movements.
In a person who is not impaired, the eyes can follow the object smoothly and without interruption. However, in a person who is impaired, the eyes may exhibit a jerking motion known as nystagmus.
Nystagmus is a rapid, involuntary movement of the eyes. When a person is impaired by alcohol or drugs, nystagmus may occur earlier and more severely than in a person who is not impaired. This can make it easier for the officer to detect impairment during the HGN test.
Limitations of the test
While the HGN test can be a useful tool for determining a DUI, it is not foolproof. Several factors can influence the test results, including certain medical conditions, the use of medications and environmental factors.
Furthermore, the officer must administer the test correctly to be effective. The officer must use a specific method for moving the object, and the test must occur in a well-lit area without any distractions.
Finally, the HGN test is just one among an extensive set of field sobriety tests. Officers may use other tests, such as the walk-and-turn test, the one-leg stand test and the HGN test to determine whether a person is impaired.
A useful test with potential drawbacks
The horizontal gaze nystagmus test is a commonly used tool for detecting impairment from alcohol or drugs. While the test can be a useful tool for detecting impairment, it is not always 100% effective and must be administered correctly to be reliable.