Police officers who suspect a driver of DUI / DWI often conduct field sobriety tests to gather evidence to support the charge. One of three standardized field sobriety tests recognized by the National Highway Transportation Safety Administration (NHTSA) is the horizontal gaze nystagmus test. A California criminal defense lawyer experienced in defending drunk driving cases can effectively challenge the outcome of the horizontal gaze nystagmus test and other field sobriety tests.
Horizontal gaze nystagmus is an involuntary jerking of the eyes as they gaze from side to side. The higher the blood alcohol concentration, the sooner the eyes will begin jerking as they move from side to side.
The officer administers the test by asking the driver to follow a small stimulus, such as the tip of a pen, with the eyes, without moving his or her head. The officer will look for a lack of smooth pursuit as the eyes move, and sustained jerking when the eye reaches the furthest point. The officer will also look for the onset of jerking prior to the eye reaching a 45-degree angle.
Each of these three factors or “clues” are counted in each eye. If the officer observes a total of four out of the six clues, the officer will conclude that there is a 77 percent chance that the driver’s blood alcohol content is above .10 percent, and the driver will be arrested for Driving Under the Influence (DUI).
However, the horizontal gaze nystagmus test is far from foolproof. Nystagmus, or involuntary jerking of the eye, occurs in everyone, regardless of whether he or she has been drinking. Alcohol and drugs magnify the nystagmus effect, but so can a variety of other factors, including illness or injury.
Remember, the officer is looking for signs of mental and physical impairment to support a charge of DUI / DWI or driving while impaired. Experts conclude that when it comes to alcohol intoxication, mental impairment always comes before physical impairment. Therefore, the mere presence of physical impairment, such as horizontal gaze nystagmus caused by illness or injury, doesn’t necessarily support a charge of drunk driving.
The conclusions of an officer who improperly administers the horizontal nystagmus test may not be admissible in court. The driver’s head and body must be facing the stimulus for this test to be valid. If the officer administers the test through the driver’s window while the motorist is sitting in the car, the test will not be valid, because the driver’s head will be turned at a 45-degree angle. An experienced DUI defense attorney can effectively challenge the results of the horizontal gaze nystagmus test by establishing when it was administered incorrectly.