Many DWI defendants come into our office and tell us that they are sure that they must have “passed” the “eye” test because they were able to follow the officer’s pen without moving their head.  We then have to explain to them that holding their head steady is not what the officer is looking at.

The following excerpt from Drunk Driving Defense, 6th Ed., by Lawrence Taylor, J.D. and Steven Oberman, J.D. generally explains what the “eye” test is and presents some basic strategies for challenging it in court:

The “Horizontal Gaze Nystagmus” (HGN) 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 almost all jurisdictions. Although administered by the officer at the scene of the traffic stop as a field sobriety test, it is really 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.

How Accurate Is The HGN Test?

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 Veterans Administration Medical Center in Cleveland, Ohio, is a noted expert in the area of nystagmus. In his article “Nystagmus, Saccadic Intrusions/Oscillations and Oscillopsia,” listing 47 different kinds of nystagmus, he 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-ophthalmologist 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.”

Further, the Court of Special Appeals of Maryland has judicially recognized 39 non-alcohol-related caused of Horizontal Gaze Nystagmus, They include:

  1. Problems with the inner ear labyrinth;
  2. Irrigating the ears with warm or cold water under peculiar weather conditions;
  3. Influenza;
  4. Streptococcus infection;
  5. Vertigo;
  6. Measles;
  7. Syphilis;
  8. Arteriosclerosis;
  9. Muscular dystrophy;
  10. Multiple sclerosis;
  11. Korsakoff’s syndrome;
  12. Brain hemorrhage;
  13. Epilepsy;
  14. Hypertension;
  15. Motion sickness;
  16. Sunstroke;
  17. Eyestrain;
  18. Eye muscle fatigue;
  19. Glaucoma;
  20. Changes in atmospheric pressure;
  21. Consumption of excessive amounts of caffeine;
  22. Excessive exposure to nicotine;
  23. Aspirin;
  24. Circadian rhythms;
  25. Acute trauma to the head;
  26. Chronic trauma to the head;
  27. Some prescription drugs, tranquilizers, pain medications, anti-convulsants;
  28. Barbiturates;
  29. Disorders of the vestibular apparatus and brain stem;
  30. Cerebellum dysfunction;
  31. Heredity;
  32. Diet;
  33. Toxins;
  34. Exposure to solvents, PCBs, dry-cleaning fumes, carbon monoxide;
  35. Extreme chilling;
  36. Eye muscle imbalance;
  37. Lesions;
  38. Continuous movement of the visual field past the eyes, i.e., looking from a moving train; and
  39. Antihistamine use.

There are three basic types of physiologic “end-point” nystagmus that are regarded as normal physiologic phenomena. These are described in Duane’s Clinical Ophthalmology. Fatigue nyustagmus has been found in up to 60 percent of normal patients when horizontal gaze is maximally deviated for at time exceeding 30 seconds. Unsustained end-point nystagmus is described as the most frequently encountered physiologic nystagmus. All experienced clinicians recognize that a few beats of nystagmus are within perfectly normal limits at gaze deviations of 30 degrees or more. Sustained end-point nystagmus begins immediately or within several seconds after reaching an eccentric lateral-gaze position. It has been found in over 60 percent of normal subjects with horizontal gaze maintenance greater than 40 degrees.

One other common  non-alcohol-related cause of nystagmus is optokinetic nystagmus. Optokinetic nystagmus is a normal type of nystagmus. A common example occurs when a passenger in a vehicle looks out the window at utility poles. The passenger’s eyes will fix on pole, and then follow it until at some point the eyes will quickly move forward to target the next pole. Optrokinetic nystagmus can also be simulated in an office setting with the patient looking at a rotating drum of alternating colors. This test is commonly use in clinical neuro-ophthalmology to provide evidence of visual function in infants or to verify lack of vision in patients who claim to be blind.

How Does The HGN Test Work?

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 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 any or all of three different ways. (Vertical nystagus, it should be noted, is a different phenomenon with different causes. 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.)

The first is to determine the angle of onset of the nystagmus. By measuring the angle at which the eye begins jerking, the officer can, theoretically, come to a rough approximation of the blood-alcohol concentration. The second method 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 technique 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 officer instructs the suspect, “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 head 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 are) 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 onset of jerking. Thus, blood-alcohol content can be roughly estimated by the angle on the device; i.e., by that point at which jerking begins. In a study for the NHTSA, researchers concluded that the onset of nystagmus (jerking) at about 40 degrees would correlate with a blood-alcohol level of .10 percent; at about 35 degrees, with a level of .15 percent; and at 30 degrees, with 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.

An alternative and increasingly common means of administering the test is simply to 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 degree, of course, this would indicate a blood-alcohol level of only .05 percent—and defense counsel may want the nystagmus evidence admitted.