What is Horizontal Gaze Nystagmus (HGN)?
The “horizontal gaze nystagmus” test is a relatively recent development in DUI investigation. The officer is attempting to estimate the angle at which your eye begins to jerk or oscillate back and forth by asking you to follow the penlight from one side to the other. If this so-called “jerking” of the eyeball occurs sooner than 45 degrees, it theoretically indicates a blood-alcohol concentration over .05%. Some officers even contend that they can estimate your exact blood alcohol concentration by what angle of onset this begins at. The smoothness of the eye’s tracking the penlight is also a factor, as is the type of jerking when the eye is as far to the side as it can go. This field sobriety test has proven to be subject to a number of different problems, not the least of which is the non-medically trained officer’s ability to recognize nystagmus and estimate the angle of onset. Because of this and the fact that the test is not accepted by the medical community, it can be thrown out as
