The nystagmus test measures involuntary eye movements and is commonly used in investigations for driving under the influence. A police officer may conduct the test during a field sobriety test, along with other standardized tests. If the driver fails the test, they may be arrested.
The term “nystagmus” refers to the involuntary movement of the eyes. A nystagmus test measures the involuntary bouncing or jerking of the eyeball. It is conducted by asking the test person to follow the path of an object, such as a pen or small flashlight, back and forth about 12 to 15 cm in front of her or her face with her eyes. The most common use of this test is as part of an investigation to determine whether a person was driving under the influence (DWI) or under the influence (DUI). If the nystagmus test subject fails the test, they could be arrested for DWI or DUI.
If a driver commits a traffic offence, a police officer can legally stop them to start an investigation. While talking to the driver, the police officer will make remarks about the driver. If the driver is having trouble producing their driver’s license and vehicle registration, smells like alcohol or has bloodshot eyes, the police officer may ask the driver to exit the vehicle and undergo field sobriety tests such as a nystagmus test.
The nystagmus test, in addition to the leg test and the walk-and-turn test, form the battery of standardized field sobriety tests. If a driver has recently consumed alcohol, their brain will have difficulty controlling the muscles in their eyes, causing the eyeball to bounce or jerk. The greater the degree of disability of the driver, the more pronounced the bouncing or jerking.
When performing a nystagmus test, the police officer must have a clear view of the driver’s eyes to examine the driver’s eyes for involuntary movements. To conduct a nystagmus test, the police officer will hold an ink pen or light pen approximately 12 to 15 inches (about 30 to 38 cm) in front of the driver’s face. The officer will instruct the driver to follow the movement of the object with her eyes. While conducting the test, the police officer will note any bouncing or bouncing of the driver’s eyeballs. If the driver fails the test, the police officer will likely have reason to believe the driver was driving under the influence and could proceed with an arrest.
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