Nystagmus is the involuntary movement, or jerking, of the human eye. The factors that can create this kind of reaction from a human being include spinning in a circle, alcohol altering the gravity in the blood, watching images that are sharply contrasting each other and pathological disorders.
The eye test, also called HGN test, is almost always performed when a law enforcement officer is trying to find probable cause to arrest someone for drunk driving (DUI).
When a law enforcement officer is ready to perform this test, they will stand in front of you. They will ask you to look at a pen, flashlight or finger. After this, they will then move the object in front of you back and forth by your face. While the law enforcement officer is doing this, they are attempting to find the following clues.
The first clue is lack of smooth pursuit. The law enforcement officer will move their pen, flashlight or finger from side to side. While doing this, they will tell you to follow the object with your eyes only, If they find any nystagmus, you will fail the test.
The second clue is nystagmus at maximum deviation. When the officer holds a person’s gaze at the corner of their eye for four seconds, they believe a drunk person will have eyes that are bouncing around a lot more than a sober person’s eyes would.
The last clue an officer is looking for is to see if a person shows nystagmus prior to their eyes being at a 45-degree angle. NHTSA guidelines claim that nystagmus prior to 45 degrees is a sign of a person having a BAC of over .08.
Is this test valid?
For this test to be valid, an officer has to make sure the test is performed in compliance with NHTSA guidelines. Many times these tests are not done according to the guidelines. This is why you should call a dui defense lawyer asap if you are arrested for drunk driving.