Police officers use the HGN field sobriety test when they suspect a driver to be operating a vehicle under the influence of drugs and/or alcohol. This is one of three standardized field sobriety tests developed by the National Highway and Traffic Safety Administration. The idea for this test is that alcohol consumption can cause a nystagmus or involuntary jerking of the eyeball when a person follows an object with their eyes. While this may be true in some circumstances, there are still many flaws to the method of proving alcohol consumption.
For starters, some people naturally suffer from a nystagmus from a type of neurological problem. Also, the police officer administering this test must adhere to all of the guidelines otherwise the test could be erroneous.
If police officers suspect a person of operating under the influence, they will have you follow an object with your eyes such as a pen with a bright light. While holding the object above your eye level so that your eyes are open wide and the officer can clearly see them, the officer will then move the object from side to side. Part of the rules state that in order to ensure eyes can focus on the object, it must be between 12 and 15 inches away.
If a driver is wearing glasses, the officer can request that they be removed so that they can see the person's eyes. However, if the person cannot see the object, they can put their glasses back on. According to the guidelines, officers cannot administer this test if the person is wearing hard contacts, has a glass eye or only has vision in one eye. For driver's with one lazy eye, the person can cover their eye with one hand and the test can be performed on each eye, one at a time.
During the HGN test, the officer will look for any lack of smooth pursuant and any jerking of the eyeball when the eye is at its maximum deviation. Remember, while the HGN test is often used as probable cause in arresting a driver for OUI, your defense attorney may be able to point out any errors that could have occurred during testing.