Nystagmus is an investigation tool used by law enforcement to determine if a person is under the influence of alcohol. After a DUI stop, a police officer, if he suspects that the driver is under the influence of alcohol, can ask the driver to step out of the vehicle and submit to several field sobriety tests. Field sobriety test is a voluntary test and you can and should refuse to submit it. If you agreed to the tests, the prosecutor will likely use them to show that you were impaired. The tests are highly subjective and can cause a person to be arrested even when he is innocent of the DUI.
The most common field sobriety tests are a visual check for nystagmus, a walk-and-turn test, a one-leg-stand test, and a preliminary alcohol screening test (PAS test).
The investigating officer will usually check for presence of horizontal nystagmus because it can indicate presence of alcohol in approximately 77% of people. A horizontal gaze nystagmus test is considered a “standardized” test because it was scientifically tested in 1975 to determine how accurately can police officers approximate the number of people who would be under the influence of alcohol. The other 2 standardized tests are Walk and Turn and One-Leg-Stand. The validity of the 1975 findings were confirmed with future “validation studies” in 1995, 1997 and 1998 in Colorado and Florida. The CHP manual states that the use of these three tests will allow the officer to determine with 90% accuracy if someone is under the influence of alcohol. For defense, having a police officer conduct a standardized field sobriety tests can be a major handicap because of its perceived accuracy.
An officer who conducts a horizontal gaze nystagmus test is required to be trained in administration of the test. If the test is not performed according to the standard criteria, the test can not be deemed valid. For example, during the nystagmus test, the subject of the test should take his glasses off and the stimulus used to administer the test should be kept at 12-15 inches from the nose of the subject. If the officer does not follow these instructions, the test will be invalid. During the nystagmus test, the officer will attempt to observe the tracking ability of the eyes, the size of the pupils, the lack of smooth pursuit (if any), if the distinct nystagmus is present at the maximum deviation, and if the nystagmus starts prior to the 45% angle.
The officer will look for 6 validated clues to determine if a person is impaired. If 4 out of 6 clues are present, the test is considered to be 77% accurate in determining that a person is above .10% BAC level. The case law, however, does not allow an officer to testify that presence of nystagum can be correlated to a specific alcohol level (People v. Loomis). Notice that a 77% accuracy means that 23% of people, or almost 1 in every 4 people, who have nysgamus will not be under influence of alcohol. For example, the nysgamust can be a neurological condition or just present with some people and completely unrelated to any alcohol consumption.
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