A nystagmus test is a common sobriety test that is used in the field to determine if an individual is under the influence of alcohol. The test is formally referred to as the Horizontal Gaze Nystagmus test. The term "nystagmus" is an involuntary movement of the eye, such as a jerking or jiggling motion.
In the field, the test is typically performed by an officer asking a detained individual to follow an object, such as a pen, with his or her eyes as it moves across the face horizontally. If the person's eyes make involuntary movements or they cannot follow the object, he or she may be placed under arrest for drunk driving. Some researches say that the nystagmus test can help determine sobriety in the field because when under the influence of alcohol the brain has a difficult time controlling eye movements. Many experts, however, argue with the use of the nystagmus test as many medical conditions can cause nystagmus to occur.
Additionally, the police officer must have a clear view of the individual's eyes in order to conduct the test properly. Because drivers are often pulled over at night when visibility is limited, the officer may use a light to see the driver's eyes more clearly. Shining a light in an individual's eyes may cause nystagmus to occur, which can alter the test results.
In Kansas, courts have previously ruled that the nystagmus test does not meet the Frye standard for scientific admissibility and is not allowed to be used in a court of law except in rare circumstances. People who were arrested for drunk driving because of a failed nystagmus test may be able to have their charges reduced or dismissed. A lawyer may be able to show that a medical condition or that the light that was shined in the detained individual's eyes could be a cause of the nystagmus, rendering the test inadmissible.