The horizontal gaze nystagmus (HGN) test is one of the most trusted sobriety exams police officers administer during a traffic stop. They often rely on the test to establish probable cause for a drunk or drugged driving arrest.
Since this field sobriety test stems from science, most defendants believe they can do nothing to refute its outcome, but that is not the case. There may be several prosecution weaknesses to exploit if the HGN test was a factor in your arrest.
More about the HGN test
According to vision experts, nystagmus is an involuntary jerking of the eye and is a common side effect of intoxication. The HGN test measures how well a driver’s eyes can track a moving object accurately and without moving involuntarily. The test typically involves following an object or a light with your eyes while the officer watches.
When the police suspect intoxication but lack evidence of alcohol use, the results of an HGN may give them cause for a drugged driving arrest.
Two possible defenses to explore
Did you know there is a specific way officers must administer the HGN test? For accuracy, they must perform each step precisely. Often they’re doing it at night when lighting conditions are unfavorable. Improper testing procedures and faulty police interpretations can open the door to a viable defense.
Another little-known fact about nystagmus is that intoxication is not its only cause. Neurological conditions, diseases and head injuries can cause involuntary eye movements. If you have medical problems, check to see if nystagmus may be a symptom or side effect. A word of caution: Some prescription drugs, like sedatives and anti-seizure medications, may cause nystagmus.
Legal guidance can help you find a defense with the best odds of success if you are facing a drug DWI in Texas.