According to their own manual, the Horizontal Gaze Nystagmus (hereinafter HGN Test) is the most reliable of the three standardized field sobriety tests. The police are trained that it is 77% accurate at detecting subjects at or above a .10% blood alcohol concentration. But that is not the whole story.
Officers are not told that everyone (EVERYONE) has nystagmus. The presence of alcohol merely enhances or magnifies this natural effect.
Officer are told that there are 40 different kinds of nystagmus, but that is somehow not important to their training. The fact that everyone has it and there are numerous non-impairing causes of nystagmus is deemed irrelevant in the decision to arrest someone. Worse yet, the police officers are given no (NO!) guidance in how to distinguish between the different kinds of nystagmus and no training about what questions to ask that would help them distinguish between an impairment or a natural event. They simply don’t care! If they see it, they will use it against you.
It is common for the officer to present evidence obtained during an HGN test at an OVI motion to suppress to support their decision to arrest. That is why it is vital to hire an OVI attorney with the training and experience to fight for you.