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Dr. L. F. Dell'Osso, Professor of Neurology at Case Western Reserve University School of Medicine, and Director of the Ocular Motor Neurophysiology Laboratory at the Veteran's Administration Medical Center in Cleveland, is a noted expert in the area of nystagmus. In an article entitled Nystagmus, Saccadic Intrusions/ Oscillations and Oscillopsia, 3 Current NeuroOpthalmology 1471 (1989), he has commented: Using nystagmus as an indicator of alcohol intoxication is an unfortunate choice, since many normal individuals have physiologic end-point nystagmus; small doses of tranquilizers that would not interfere with driving can produce nystagmus; nystagmus may be congenital or consequent to neurologic disease; and without a neuro-opthalmologist or someone knowledgeable about sophisticated methods of eye movement recordings, it is difficult to determine whether the nystagmus is pathologic. It is unreasonable that such difficult judgments have been placed in the hands of minimally trained officers. Dr. Dell'Osso also lists 47 different kinds of nystagmus in the article. The test is essentially a measurement of the movement of the eye. Simply stated, nystagmus means a jerking of the eyes. Although there are different types of nystagmus, the type involved in DUI field sobriety testing is "horizontal gaze nystagmus," that is, the involuntary pendular (back and forth) movement of the eye. This type of nystagmus is commonly measured by the officer in one, two, or all of three different ways. Vertical nystagmus, it should be noted, is a different phenomenon with different causes than horizontal. Although often testified to by police officers on the issue of alcohol intoxication, the relevance of vertical nystagmus is primarily to indicate the presence of drugs in the body. |
Copyright 2001 - 2008 |
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The first part of the test is to determine the angle of "onset" of the nystagmus. By measuring the angle at which the eye begins jerking, the DUI officer can theoretically come to a rough approximation of the blood alcohol concentration. The second part is to notice whether the jerking becomes more "distinct" when the eye is moved to the lateral extreme - that is, when there is no longer any white of the eye visible at the outside of the eye. The third part is to notice the lack of "smooth pursuit": rather than following a moving object smoothly, the eye jumps or "tugs." To administer the test, the DUI officer instructs the suspect to "keep your head straight ahead and follow this object with your eyes." The officer then moves a finger or pencil, or a penlight at night, from the center of the device steadily toward one side. The object is held 12 to 15 inches directly in front, 2 to 3 inches above the eye being tested. The object is moved slowly (three to four seconds to complete the arc) in a level, even arc - maintaining the 12 to 15 inch distance. At the onset of nystagmus, the object is held for one to two seconds at the point and the officer notes the angle of onset. The jerking should continue as long as the individual stares at the object, even though it is no longer being moved. The officer then repeats the test with the other eye. The eyes of a person under the influence of alcohol will begin to jerk sooner than those of a sober person, and the more intoxicated the individual the sooner the jerking. Thus, in theory blood alcohol content in DUI investigations can be roughly estimated by the angle on the device; i.e., by that point at which jerking begins. In a study for the National Highway Traffic and Safety Administration, researchers concluded that the onset of nystagmus (jerking) at about 40 degrees would correlate with a blood-alcohol level of .10 percent; a level of .15 percent would be indicated where the involuntary movement began at about 35 degrees; onset at 30 degrees indicates a level of about .20 percent. Individuals with blood-alcohol levels above .20 percent often cannot even follow a moving object with their eyes. Thus, theoretically, a rough formula may be used to arrive at blood-alcohol content: Simply subtract the angle from 50 and convert to percent; for example, an angle of 37 degrees would convert to .13 percent blood alcohol. See V. Tharp, et al., Psychophysical Tests for DUI Arrest, DOT-HS-8-01970, 1981. An alternative and increasingly common means of administering the test in DUI cases is to simply determine if jerking begins before the eye reaches a 45-degree angle. This is usually observed by the officer without the aid of any angle-measuring device, and obviously would be subject to question during cross-examination. If the jerking began at about 45 degrees, of course, this would indicate a blood-alcohol level of only .05 percent - and defense counsel may want the nystagmus evidence admitted. |
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A new type of DUI field sobriety test arose in the early 1980s in the western states. Used initially only on an experimental basis, the test quickly spread and is now being used by police agencies in DUI investigations throughout the country. This is the "horizontal gaze nystagmus" test. Although administered by the officer at the scene of the traffic stop as a field sobriety test, it should be recognized as, in reality, a superficial test to determine blood-alcohol content. It should also be recognized that evidence of the test can have devastating effects in a drunk driving trial. Properly handled by the defense, however, this test may never be admitted into evidence; if admitted, the test can be discredited.