Horizontal Gaze Nystagmus

To properly cross-examine an officer, an 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 because there are many known causes of nystagmus. These include the time of day, brain damage from prior trauma, depressants and stimulants. In addition, 5 to 7 percent of people have nystagmus without any known cause.

Prior to beginning the HGN test, an officer is taught to explain to clients that he or she is going to check their eyes, to keep their head still while following the stimulus with their eyes only and to keep following the stimulus with their eyes until the officer tells them to stop. The stimulus is to be positioned approximately 12 to 15 inches from the client’s nose and slightly above eye level.

Three Clues When Testing

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 seconds out and two seconds 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 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, it should be held there for a minimum of four seconds. This test must be repeated for both eyes. Holding the eye for at least four seconds is important because everyone’s eyes may bounce once initially taken to maximum deviation. It is the nystagmus that is present after four seconds that indicates 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 a 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 a 45-degree angle.

The most common mistake arresting officers make is testing too quickly. If you can get the officer to admit that he or she was trained according to National Highway Traffic Safety Administration standards, that the test is valid only if conducted according to NHTSA standards and that he or she changed elements of the test (by going too fast, too slow, moving the stimulus too far out or too close, not repeating each test, etc.), the officer must therefore admit that the accuracy of the tests is compromised and they cannot be used as valid indicators of intoxication.

Free Consultation With a Drunk Driving Defense Lawyer

If you have questions about the horizontal gaze nystagmus test or other field sobriety tests, contact Travis Noble, P.C., in St. Louis, Missouri, by calling (314) 721-6614.

Practice Areas