Horizontal Gaze Nystagmus (HGN) DUI Evidence

The Horizontal Nystagmus (HGN) Eye Test is one of three comprise “Standardized Field Sobriety Tests (SFST) developed and approved by the National Highway Traffic Safety Administration (NHTSA) for DUI field testing. The Horizontal Gaze Nystagmus (HGN) eye test. Although scientific studies done through the NHTSA research establishes it as a reliable DUI roadside test; some trial courts still do not allow the admittance of them as evidence against a defendant. This is because in many cases, the results were argued to be invalid due to weaknesses or error in administration, equipment, and preparations of the HGN test results were found in many cases to be insufficient to satisfy the court’s evidentiary standards. As a result many jurisdictions only allow admittance to establish “Probable cause” for arrest, or not at all. Due to the history of inaccuracies and arguments in their validity, they are often strong areas of challenge by defense.

Horizontal Gaze Nystagmus (HGN) of the Eye

A Horizontal Gaze Nystagmus (HGN) is an involuntary bouncing, jerking or rapid movement of the eye laterally or horizontally, when the eye gazes from side to side. The NHTSA studies hold that an impaired driver under the influence of alcohol or other depressant of the central nervous system is unable to correct or control their eye muscles. This causes the involuntary movement of the eye, associated with HGN. The theory is that the degree of impairment or the Nystagmus becomes greater or more pronounced, as the degree of intoxication or drug influence increases.

Administration of Horizontal Gaze Nystagmus (HGN) Test

To conduct an HGN test, the police officer instructs the suspect to follow an object such as a penlight, with their eyes only, keeping their head still. The officer stands in front of the suspect, and places the light pen at approximately 12 inches from the suspects face, just over the eye level. The officer must ask the suspect if they suffer from a medical impairment related to the eye such as a pre-existing Nystagmus that could result in inaccurate results or misconception of being under the influence of alcohol. If the suspect does, but still agrees to the eye test, the police may proceed. But they are required to document the pre-existing eye impairment in the report. The officer will start in the middle of the face, and test each yet separately.

What police are looking for in the HGN Test

While administer the test officer looks for three "clues," (or six considering both eyes are tested). The officer will test each eye separately for indications of the following:

  1. Lack Of Smooth Eye Rolling Movement;
  2. Certain And Sustained Nystagmus For At Least 4 Seconds;
  3. Angle Of Onset Of Nystagmus Prior To 45 Degrees From The Center Of The Face Or Where The Pen Light Is Moved To The Top Of The Suspect’s Shoulder

Phoenix DUI Defenses for HGN Testing

There are a number of other defenses for the HGN test evidence including the fact that the HGN may actually cause a Nystagmus. Experienced Lawyers who defend DUI charges in Phoenix on a regular basis are very familiar with the SFST training manual and rules regarding administration and reporting of the HGN test. If there are deviations from the NHTSA rules and protocol, they will move to have the HGN dismissed or suppressed due to the deviations. The reason for this is that the deviation, however, slight may have compromised the validity and accuracy of the test.

DUI Lawyer Phoenix Arizona

The HGN eye test is one of three Standard Field Sobriety Test. Despite the fact that it is recognized by the National Highway Traffic and Safety Administration, it can sometimes produce inaccurate conclusions related to impairment. The same is the case for other roadside DUI testing.

If you were arrested for an impaired driving offense, whether or not included SFST results, it is important that you consult experienced DUI defense attorney. James Novak, is well versed on all aspects of DUI cases, and is highly skilled in challenging evidence including SFST results. He is a former prosecutor, in Maricopa County, with a great deal of litigation and defense experience.

James Novak provides a free initial consultation and serves clients in Phoenix East Valley cities including Gilbert, Chandler, Mesa, and Tempe. Call today for your free consultation (480) 413-1499.