There are three Field Sobriety Tests that an officer might use when assessing if a driver is intoxicated and one of these is known as the Horizontal Gaze Nystagmus, or the HGN test. The purpose of this exam is to assess for the presence of nystagmus which can be caused by the consumption of alcohol in some cases. Nystagmus is the involuntary jerking of the eye and horizontal gaze nystagmus is when the jerking occurs as the eye moves side to side. The consumption of alcohol can begin to restrict the brain from controlling the eye muscles correctly which is when it can begin to look like more of a jerking motion. The greater the level of alcohol impairment, the more the bouncing motion can begin to occur.
When an officer is assessing a suspect, they are going to look at a number of details to determine if the driver is impaired by alcohol. The HGN test is one of the things they can use and it will involve three different tests in both eyes. An officer will use an object such as a pen or flashlight and ask the suspect to follow it with their eyes. The officer will first be looking for equal tracking, or if the individual is able to follow the object smoothly with their eyes. Next they will be looking for the onset of nystagmus when the eye is brought out to maximum deviation. In order to make sure that the quick movement is not what created the possible nystagmus, the officer should have the individual hold their eye at maximum deviation for around four seconds. The last thing they will be looking for is if the nystagmus occurs before the eye is brought out to a forty five degree angle. For further understanding of field sobriety tests and how they can be defended against, contact a Springfield OUI lawyer at my firm.