Drivers in Illinois facing possible DUI charges may go through a series of tests to determine if they are under the influence of alcohol, drugs or another substance. One of the common tests performed for this purpose is the nystagmus test. It’s a type of test that assesses an individual based on involuntary eye movements. It’s conducted by asking an individual to follow either a small flashlight or pen with their eyes as the object is moved back and forth in the front of the person’s face from about 12 to 15 inches away, usually after being asked to step out of their vehicle.

Even though a failed nystagmus test often results in an arrest, a DUI defense attorney may challenge the results. However, it is legal for a driver to be stopped and tested if they commit a clear traffic violation, such as swerving on the road or running red lights. It’s often when a driver is having trouble speaking or showing other signs of being under the influence that they are asked to submit to a nystagmus test and other field sobriety tests.

Specifically, it’s consuming alcohol that tends to affect muscles in the eyes. This is what results in the bouncing and jerking of the eyeball when an attempt is made to follow a pen, finger or flashlight. When the test is conducted, a law enforcement official will instruct a driver suspected of being impaired in some way to follow the movements of an object. The official will then take note of any bouncing or jerking eye movements they observe.

While failing a nystagmus test is normally enough to have probable cause to make a DUI arrest, it may be possible for an attorney to put together a DUI defense that challenges the results of this type of field sobriety test. For instance, a lawyer might present evidence that a driver has a medical condition that affects their eye movements. DUI defenses may also include challenges to the reason a driver was pulled over in the first place or the way on-the-scene tests were conducted.