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What does an eye test have to do with DUI?

On Behalf of | Apr 30, 2024 | DUI

Imagine that a Missouri police officer flashes lights behind a motorist to initiate a traffic stop. The driver pulls over and after a few questions, the officer asks him or her to step out of the vehicle. Then, the law enforcement officer asks the driver to take a horizontal gaze nystagmus (HGN) test. This is an eye test that may establish probable cause for a DUI arrest. 

When police administer an HGN test, they usually use an object such as an ink pen or their index finger, which they instruct the participant to track using their eyes only, not moving the head. The officer then moves the object left to right or vertically and observes the individual’s eyeballs as they track the object. If the eyeballs move erratically, like a shaking or jerky movement, horizontal nystagmus is present, typically a sign of intoxication.  

Can a DUI arrest occur if a driver refuses to take an HGN test? 

A motorist can refuse to take an HGN test or any other preliminary alcohol screening test during a traffic stop. There is no penalty for refusing. However, not taking the test does not guarantee that a DUI arrest will not occur anyway because there are other ways for police to establish probable cause.   

If an individual takes an HGN test during a Missouri traffic stop and fails, the officer will take them into custody for suspected DUI. If this happens, it is wise to focus on preparing a strong defense. Most people do this by requesting a consultation with a criminal defense attorney.