Horizontal Gaze Nystagmus

Accuracy of the HGN

The Horizontal Gaze Nystagmus (HGN) Test is considered the most accurate of all the Standardized Field Sobriety Tests. The HGN is the test where a police officer will ask the driver to follow his finger, a pen, or a pen light with the driver’s eyes, without moving the driver’s head.

The HGN is also the test that police officers rarely administer properly. Police officers are frequently improperly trained in the HGN, and so they will perform the test improperly, and the results, therefore, are not accurate.

HGN Clues Explained

For instance, the police officer is supposed to make sure that driver is not near any flashing lights, must place the pen, finger, or pen light approximately 12 inches from the driver’s eyes, must place the pen light slightly above the eyes, and must hold the pen, finger or pen light for at least four seconds at either side.

In addition, the police officer is not supposed to perform the HGN test while the driver is seated in the driver’s seat. The driver should be standing (or sitting) outside of the car so that the driver’s neck is not twisted.

The police officer is looking for involuntary movement of the eye (jerking) as it moves from left to right.

The police officer should also ask the driver a series of questions about his medical history to make sure that the driver does not suffer from a condition that might cause nystagmus independent of drinking.

HGN Flaws and Errors

There are many different kinds of nystagmus, including nystagmus caused by head trauma, certain diseases, problems with the inner ear, certain medications, excessive consumption of caffeine, and so forth. Therefore, a person might show nystagmus even though that person is not drunk or impaired.

If an officer does not ask screening questions, then he can’t tell whether the nystagmus he observes is a result of something other than alcohol consumption.

Many officers fail to conduct this test properly and, as a result, a skilled Raleigh DWI lawyer may be able to show that the test is worthless in court.

Finally, the HGN test is considered a scientific test, and so certain rules apply when it is admitted into court. A skilled Raleigh criminal lawyer may be able to keep the test out of court by showing that the prosecution has failed to lay a proper scientific foundation for the test at trial.

Current HGN Law

North Carolina Appellate Courts have recently ruled that the HGN test is only admissible in court if the witness is qualified as an expert witness pursuant to Rule 702 of the Rules of Evidence.  In State v. Godwin, the court held:

In accordance with Helms, therefore, Rule 702(a1) requires that before a witness can testify as to the results of an HGN test, he must be “qualified as an expert by knowledge, skill, experience, training, or education.” If the witness is so qualified and “proper foundation” is established, the witness may “give expert testimony” as to the HGN test results, subject to the additional limitations in subsection (a1). N.C. Gen. Stat. § 8C-1, Rule 702(a1). Namely, the expert witness may testify “solely on the issue of impairment and not on the issue of specific alcohol concentration,” and the HGN test must have been “administered by a person who has successfully completed training in HGN.”

Walk and Turn Test


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