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Understanding the Nystagmus Field Sobriety Test in a San Diego DUI Case

Whenever an officer follows a vehicle for a suspected DUI. The first field sobriety test any officer performs in the field is the horizontal gaze nystagmus to determine whether there is a possibility of impaired driving. Under the horizontal gaze nystagmus test, the officer observes smooth pursuit, nystagmus prior to a 45-degree angle, and nystagmus at maximum deviation.

There are conditions that will interfere with the test. Outside weather conditions and distractions have a negative affect on the Nystagmus test. However, medical conditions such as past concussions will provide false positive results for nystagmus based on impairment.

The officer is required to provide the following instructions before conducting the examination:

1. Suspects must remove their glasses if wearing any
2. Suspects must put feet together and place hands by sides
3. Suspects must keep head still while looking at the stimulus
4. Suspect must follow movement of stimulus with eyes only & do not stop looking at stimulus until test over
5. Position stimulus approximately 12 to 15 inches from nose in and slightly above eye level to start test
6. Check equal tracking of eyes
7. Check equal pupil size
8. Check lack of smooth pursuit (start with left eye, move stimulus 2 seconds to each side & perform twice each eye)
9. Check eyes for distinct nystagmus at maximum deviation (start with left eye, move stimulus 2 seconds to each side & hold in maximum position for 4 seconds & perform twice each eye)
10. Check eyes for onset of nystagmus prior to 45 degrees (start with left eye, move stimulus 4 seconds to reach suspects shoulder & stop to verify jerking continues)
11. Check vertical nystagmus.
12. Total the clues.

It is important for the officer to count the clues to determine probability of impairment. If the test is performed correctly, then there is a total of six clues for two passes for each eye for lack of smooth pursuit, distinct nystagmus at maximum deviation, and onset of nystagmus prior to 45 degrees. An officer just needs a minimum of four clues to determine if the suspect’s BAC level is above a .08%

If you have any questions about your DUI in San Diego, contact San Diego DUI specialist Attorney Vik Monder at 619.405.0063 or visit San Diego Criminal Defense Attorney