Horizontal Gaze Nystagmus Test

Drivers under investigation for DUI / DWI typically take field sobriety tests before being arrested. Although many drivers hope they will avoid arrest by "passing" the tests, field sobriety tests exist only to justify an arrest and gather evidence for a court case.

There are two kinds of field sobriety tests: Standardized and Non-standardized. The Horizontal Gaze Nystagmus test is one of three field sobriety tests standardized and recognized by the National Highway Traffic Safety Administration (NHTSA). A skilled DUI / DWI attorney from The Kavinoky Law Firm can successfully challenge the results of a Horizontal Gaze Nystagmus test or other field sobriety tests.

Horizontal gaze nystagmus is an involuntary jerking of the eyes as they move from side to side. The Horizontal Gaze Nystagmus Test is based on the theory that the greater the driver's blood alcohol content (BAC), the sooner the eyes will begin jerking as they move from side to side.

The officer instructs the driver to follow a small object such as the tip of a pen using only the eyes. Police watch for uneven eye movement or sustained jerking when the eye reaches the furthest point. The officer also will make note if the eye begins jerking before it reaches a 45-degree angle.

Each of these three occurrences counts as a "clue" when observed in each eye. If the officer notes at least four of the six signs, he or she will conclude that there is a 77 percent chance that the driver's BAC is greater than .10 percent, and the individual will be placed under arrest for drunk driving.

Although it is standardized by the NHTSA, the Horizontal Gaze Nystagmus Test is far from foolproof. Nystagmus, or involuntary jerking of the eye, occurs in every individual, regardless of whether he or she has been drinking. Alcohol and drugs may intensify the nystagmus effect, but so can many other factors, including injury or illness.

When an individual drinks alcohol, mental impairment always occurs before physical impairment. Physical impairment can be masked by those with a high tolerance for alcohol, but mental impairment cannot be hidden. Therefore, the mere presence of physical impairment such as involuntary eye jerking doesn't mean the driver was under the influence of alcohol.

Some officers don't even administer the Horizontal Gaze Nystagmus Test properly, and their conclusions may be inadmissible in court. The driver's head and body must be facing the object, so if the officer conducted the test through the driver's-side window, the results may be inadmissible because the driver's head was turned at a 45-degree angle.

Luckily for accused drunk drivers, field sobriety tests don't always hold up in court. The officer's conclusions can be successfully rebutted during cross-examination. An experienced California DUI / DWI attorney can effectively challenge the results of the Horizontal Gaze Nystagmus Test and create reasonable doubt concerning the driver's guilt.