The "horizontal gaze nystagmus" test, is a relatively recent development in DUI investigation. The officer attempts to estimate the angle at which the eye begins to jerk ("nystagmus" is medical jargon for a distinctive eye oscillation); if this occurs sooner than 45 degrees, it theoretically indicates a blood-alcohol concentration over .05%. The smoothness of the eye's tracking the penlight (or finger or pencil) is also a factor, as is the type of jerking when the eye is as far to the side as it can go.
This field sobriety test has proven to be subject to a number of different problems, not the least of which is the non-medically trained officer's ability to recognize nystagmus and estimate the angle of onset. Because of this and the fact that the test is not accepted by the medical community, it is not admissible as evidence in many states; it continues, however, to be widely used by law enforcement.
The following cross-examination by a prominent California drunk driving defense attorney is an excellent example of how to deal with the nystagmus test in a drunk driving criminal case. It shows how a lawyer can successfully make a jury question the testimony of the police officer.
Attorney - Tell me, sergeant, are you licensed anywhere in this country to diagnose eye disfunction?
Officer - Of course not.
Attorney - To determine physiological causes of nystagmus?
Officer - No.
Attorney - Well; how many times have you qualified as an expert in court on the physiology of the eye?
Officer - On the physiology of the eye, I have not.
Attorney - How many times on the physiological effects of alcohol on eye musculature?
Officer - Never.
Attorney - Sergeant, did you receive training in nystagmus at the highway patrol academy?
Officer - I did.
Attorney - How many hours?
Officer - As I recall, it was six hours of demonstration and instruction.
Attorney - How many hours do all recruits or officers get?
Officer - Six hours.
Attorney - So, you got the same training as any other police officer?
Officer - Correct.
Attorney - Then you did not receive any special training in nystagmus, other than what everyone routinely gets?
Officer - No.
Attorney - Who were your teachers?
Officer - My teachers?
Attorney - Yes. Who instructed you on nystagmus?
Officer - The training officer. I don't recall his name.
Attorney - Another highway patrolman, like yourself?
Officer - Yes.
Attorney - Then, the only training you received on nystagmus was from another police officer?
Officer - That's correct.
Attorney - You'd received no training from qualified physicians?
Officer - No.
Attorney - Sergeant, what does cause nystagmus?
Officer - What do you mean?
Attorney - Nystagmus—jerking of the eyes..... What causes it?
Officer - What causes it?
Attorney - Yes. Could you please explain the physiology of normal nystagmus.
Officer - I'm not sure I can.
Attorney - Well, can you explain the chemical effects of alcohol on that physiological process?
Officer - Alcohol makes the jerking start earlier.
Attorney - Yes, but why?
Officer - I don't know.
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