If you are stopped for DUI in Virginia, then the police officer may have you perform a field sobriety test known as the Horizontal Gaze Nystagmus test. This field sobriety test is approved by the National Highway Traffic Safety Administration. When an Officer asks you to perform this field sobriety test, s/he will be looking for any involuntary jerking of the eyes, which is often caused from alcohol consumption. However, nystagmus can occur naturally and/or without the presence of alcohol consumption.

The Officer will instruct you to follow a stimulus such as a lighted pen or a flashlight horizontally with your eyes. In each eye, the Officer is looking for three clues: 1) a lack of smooth pursuant when following the stimulus; 2) any jerking occurring when the eye is looking at the stimulus at maximum deviation; and, 3) any jerking that starts before 45 degrees. If the Officer notices four factors occurring between the two eyes, it is likely that your blood alcohol content is at least .10% and is over Virginia's limit of .08%.

Failing the HGN field sobriety test does not automatically result in proof that you were driving under the influence of alcohol. In fact, many people suffer from a natural nystagmus in their eyes. There are other factors that may trigger nystagmus, such as: the Officer moving the stimulus too quickly, making the stimulus come to close to your eyes or by not allowing you enough time to follow it during the test. Furthermore, despite its approval by NHTSA, many courts have ruled that the test is not scientifically reliable.