Which sobriety test detects involuntary eye movement?

The horizontal gaze nystagmus test is specifically designed to detect involuntary eye movement, which can indicate alcohol impairment. This test assesses the way the eyes track a moving object, such as a pen or a finger, and looks for the presence of nystagmus—an involuntary jerking of the eyes that can occur when a person is under the influence of alcohol.

During the test, the officer observes the eyes as they follow the object from side to side. If the eyes exhibit nystagmus at certain angles or if the onset of nystagmus occurs before a 45-degree angle, this can suggest higher levels of impairment. This ability to reliably measure eye movement makes this test an important tool in field sobriety testing, linking physical reactions to alcohol consumption.

In contrast, the other tests mentioned focus on different aspects of motor skills and balance, with no specific evaluation of eye movement. The walk-and-turn test and one-leg stand test assess the subject's balance and coordination, while the field observation test generally combines various factors observed by the officer rather than measuring a specific physiological response like eye movement.