Horizontal Gaze Nystagmus

Motorists suspected of drunk driving in New Jersey are usually asked to take a field sobriety test before being arrested. There are two types of field sobriety tests – standardized and non-standardized. One of three standardized field sobriety test recognized by the National Highway Traffic Safety Administration (NHTSA) is the horizontal gaze nystagmus (HGN) test.

The HGN test is not admissible in New Jersey courts to prove guilt. Even so, officers still administer the test.

Horizontal gaze nystagmus refers to an involuntary jerking of a person’s eyes as they move from side to side. The horizontal gaze nystagmus test is based on the idea that the higher an individual’s blood alcohol concentration (BAC), the more quickly his or her eyes will begin jerking as they move from side to side.

When taking the test, the driver is told to follow a small stimulus, such as the tip of a pen, with the eyes only, while keeping the head stationary. Police watch for a lack of smooth tracking as the eyes move, and any sustained jerking when the eye reaches the furthest point. The officer also will watch for any jerking that occurs before the eye reaches a 45-degree angle.

If any of these instances occur in either eye, it is considered a “clue.” If the officer records four out of the six possible clues, he or she will determine that there is a 77 percent chance that the driver’s BAC is 0.08 percent or greater, and a driving under the influence arrest will follow, even though the test results are not admissible of guilt of the driver in a New Jersey DWI / DUI charge.

However, the horizontal gaze nystagmus test is far from foolproof. Alcohol and drugs magnify the nystagmus effect, but everyone experiences nystagmus, or involuntary jerking of the eye, to some degree. A number of other factors can also increase nystagmus, including illness, fatigue, and injury.

To understand how the horizontal gaze nystagmus test and other field sobriety tests can be effectively challenged, it’s helpful to understand how alcohol affects the central nervous system. Alcohol use causes both mental and physical impairment, but when an individual drinks alcohol, mental impairment always occurs before physical impairment. Therefore, if the driver exhibited physical difficulties but no mental impairment, it must have stemmed from a source other than alcohol.

The inherent flaws of the horizontal gaze nystagmus test are compounded by the fact that many officers don’t conduct the test correctly. The driver’s head and body must be facing the object of stimulus. If the driver was sitting in a vehicle when the test was performed, the results will not be valid, because the driver’s head was turned at a 45-degree angle. If the driver was facing traffic or flashing lights, the results may be invalid, as well.

Many motorists accused of a New Jersey DWI fear that a poor performance on the horizontal gaze nystagmus test means an automatic conviction, but that’s just not true, as the results are not admissible in a New Jersey court to demonstrate guilt of the driver on a New Jersey DWI charge. A skilled New Jersey DWI attorney at Levow DWI Law, P.C. with experience defending drunk driving cases will aggressively challenge the driver’s horizontal gaze nystagmus test and the other field sobriety exercises as part of a strategic defense plan.

Please contact the offices of Levow DWI Law, P.C. today for a free consultation.