HGN Testing
– MT, Texas
Answer:
One of the most common tests performed by Austin area police to determine whether someone is driving while intoxicated (DWI) is the horizontal gaze nystagmus test. Studies have shown a correlation between blood alcohol level and the jerky movement of the eyes.
Generally a police officer will have the suspect hold his or head level. The police will ask the suspect to track an object with their eyes. One of the problems with the test from a trial standpoint is that the test is almost never properly captured on video.
Additionally, the police vehicle is parked far enough away to capture on film the suspect’s whole body. The test is generally done with the suspect sideways to the police car so that the car’s lights don’t “interfere” with the test.
At trial the jury sees the officer standing, moving the pen or light sideways. You can’t see the suspect’s eyes. The jury has to depend on the officer (who usually shows up in a shiny uniform) to describe what they saw. Of course the officer going to say he or she saw the clues. This generally benefits the prosecutor.
However, there could be an opportunity for the defendant’s attorney. If the officer has made other mistakes, such as getting the time wrong or getting other details of the incident wrong, then the defense attorney can argue that if the cop made one mistake, they made others as well.
Another plus for the defense is that there is only a 80 to 90 percent correlation between the test and blood alcohol level. That means there’s a TEN to TWENTY percent chance of a blood alcohol level less than .08.
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