In order to properly cross-examine an officer, the attorney must master the proper administration and scoring of the horizontal gaze nystagmus test.
Nystagmus is an involuntary jerking of the eye. Horizontal Gaze Nystagmus refers specifically to the jerking of the eye when the eye looks to the side. The HGN test itself can be an inaccurate indication of intoxication for the reason that there are many known causes of nystagmus. These include but are not limited to the time of day, brain damage from prior trauma, or other depressants or stimulants. In addition, 5-7% of people have nystagmus without any known cause!
Prior to beginning the HGN test, the officer is taught to explain to the client that he is going to check their eyes, to keep his head still while following the stimulus with his eyes only, and to keep following the stimulus with his eyes until the officer tells the client to stop. The stimulus is to be positioned approximately 12 to 15 inches from the clients nose and slightly above eye level.
There are three clues the arresting officer is supposed to test for when administering the HGN test. The first is a lack of smooth pursuit. This refers to the jerking of the eye as observed when the eyes are following a stimulus from side to side. It should take approximately two second pace out and two second pace back to test each eye for a lack of smooth pursuit. Then, it is to be repeated.
The second clue the officer should test for is distinct nystagmus at maximum deviation. This test is to determine whether the client's eye will bounce if it is taken as far to the side as possible. Once the eye is taken as far to the side as possible, the eye should be held there for a minimum of four seconds. This test must be repeated for both eyes. The requirement of holding the eye for a minimum of four seconds is important because everyone's eyes may bounce once initially taken to maximum deviation. It is the nystagmus that is present after the four seconds that is the indication of intoxication.
Finally, the last clue to test is the onset of nystagmus prior to 45 degrees. The stimulus is slowly moved across the client's eye at a rate that would take approximately four seconds to reach from the client's nose to his shoulder, which is approximately the 45 degree angle. Both eyes are to be tested twice. It is a clue of intoxication if the officer observes the eye jerking prior to taking the stimulus out to the 45 degree angle.
The most common mistake made by the arresting officer is that they do the test too fast. If you can get the officer to admit that he was trained according the NHTSA standards, that the test is only valid if conducted according to NHTSA standards and that he changed the elements of the test (by going too fast, too slow, moving the stimulus too far out or too close, not repeating each test, etc.), he must therefore admit that the validity of the tests are compromised and cannot be used as valid indicators of intoxication!
