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The name alone is intimidating. The horizontal gaze nystagmus (HGN) test is used by law enforcement officers – often in conjunction with other tests – to determine if a suspect has been drinking. You might be wondering what a test with such an imposing sounding name is really all about, and how accurate it is in determining whether or not you’ve had too many drinks to drive.

Logic behind the HGN test

The HGN test is included as one of three tests recommended by the National Highway Traffic Safety Administration (NHTSA) for determining if a subject is too intoxicated to drive. According to NHTSA, a nystagmus is an involuntary jerking or bouncing of the eyeball that occurs when there is a disturbance of the inner ear system or of control of the eye. Horizontal gaze nystagmus (HGN) refers to a horizontal jerking when the eye gazes to the side.

Alcohol consumption impairs the ability of the brain to correctly control eye muscles, therefore causing the jerk or bounce associated with HGN. In theory, as a person becomes more intoxicated, the jerking or bouncing, i.e. the nystagmus, becomes more pronounced. NHTSA researchers claim that the HGN test was 77% accurate in detecting whether an individual's BAC was .10 or higher.

Administering the HCN test

To administer the HCN test, an officer asks the subject to keep his or her head still and follow a pen or other object that the officer moves horizontally in front of each eye. The test must be administered in a well-lit area or the officer must use a flashlight to illuminate the subject’s face. The subject should not be facing towards the blinking lights of the police cruiser or passing cars, which can cause the eye to react.

The officer looks for three indicators of impairment:
1. the subjects eye cannot smoothly follow the movement of the pen or other object
2. the subject’s eye exhibits a distinct jerking when the pen or object is moved to the far side of their field of vision
3. the subject’s eye begins to jerk before the pen or object is moved 45 degrees from the center of the subject’s face. If and officer can identify 4 or more clues, then the officer can conclude that the accused is probably impaired.

Issues with the HCN test

There are several issues that may affect the admissibility of HGN test results:

1. Whether the HGN test is characterized as scientific or as simply an observation of a physical trait
2. If HGN is deemed scientific, whether it is reliable
3. Whether the law enforcement officer is properly trained to administer the HGN test
4. Whether the officer properly administered the test in the particular case
5. The purpose for which the HGN test result will be used.

If you need help because you have been accused of driving under the influence, an attorney skilled with DUI litigation can review the results of any tests you receive and help spot any potential issues. Please contact Weisberg & Zaleski to discuss your DUI case with you for no charge and no obligation.

Weisberg & Zaleski, P.C.
112 College Place
Norfolk, VA 23510

Toll Free: (800) 690-0235
Phone: (757) 622-7740
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