DUI Defense Strategies (cont’d.)
When a DUI lawyer analyzes the horizontal gaze nystagmus portion of your case, he/she expects to learn that the DUI police investigator observed something called “a distinct nystagmus” in your eyes.
This means that there was alcohol in your blood.
By definition, a nystagmus occurs when a person’s eye moves in a jerky motion as opposed to a smooth motion. When a person has alcohol in their system, the eye will begin to move in this jerky motion. When there is no alcohol in a person’s system, the eye should move smoothly.
Therefore, to test for the influence of alcohol, DUI cops will ask a DUI suspect to submit to roadside testing and he/she will look in the suspects eyes to see if they exhibit any nystagmus.
To determine if the DUI suspect exhibits a nystagmus, the DUI officer will ask the suspect to track the light at the end of a handheld pen light. As the officer moves the pen light from right to left, he/she will observe how the DUI suspect’s eyes move.
If the police officer observes any jerky motion,
he/she will certainly attribute such observation to the influence of alcohol.
While this test can be effective, it has a number of very important limitations. They are as follows:
Limitations of Horizontal Gaze Nystagmus Test
- HGN is ineffective in chemical or controlled substances cases.
- HGN does not indicate whether or not a person is impaired.
- If a person is impaired, HGN does not measure the extent of impairment.
- Some people have a natural nystagmus that has nothing to do with impairment.
Regardless of what the officer wrote in his/her report, a DUI lawyer must consider the evidence in context. Knowing the limitations, applicability, and misinterpretation of evidence is just as important.
For instance, a person may have a nystagmus from drinking alcohol, but may not be impaired because they have a higher than normal tolerance. At the same time, a DUI suspect may be one of the few people who have a natural nystagmus.
When I was a DUI prosecutor years ago, I completed specialized DUI training. During this school, I was used as a subject to demonstrate the horizontal gaze nystagmus. Much to my surprise, at ten o’clock in the morning, while not under the influence of anything but cereal and a banana, my eyes showed a natural nystagmus!
I wear eye glasses with a very weak prescription to correct my nearsighted vision, but am otherwise 100% healthy with no known problems.
As a DUI lawyer, this was a major learning experience and it taught me to look for such surprises in other people’s cases. As a DUI defense lawyer I apply this lesson and take nothing for granted. Instead, every minute detail of every case must be explored with a mind open for the possibility that a valid defense may be uncovered when it is least expected. For that reason, being thorough is tantamount for success.