Cross-Examination on Horizontal Gaze Nystagmus in a Drunk Driving Case

A standard DUI field sobriety test is the “horizontal gaze nystagmus” test. Nystagmus is a medical term for a distinctive eye oscillation. It is detected when an eye is following an object from one side to the other and under observation the eye begins to jerk. The officer will try to recreate this by having the suspect follow a penlight from side to side and guess the angle at which it begins to jerk, using none of the proper tools. If the angle the officer guessed occurred sooner than 45 degrees, it theoretically implies BAC (blood-alcohol content) over .05%. Other factors affect the actual BAC including the overall smoothness of the eye, and how the eye jerks when it reaches the other side.

Riddled with problems, this test isn’t allowed as evidence in many states. This is because of the ridicule received from the medical community over the poor application of the test. One of the smaller deficiencies is the fact that officers aren’t trained to recognize nystagmus and the angel it starts at. Contrary to these facts the test is still widely used by law enforcement.

For a demonstration of how to deal with the "eye test" in a drunk driving criminal case, see the nystagmus cross-examination by a prominent San Diego DUI lawyer at the "California DUI" website.

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