Horizontal Gaze Nystagmus (HGN) Test

If you have been arrested for a DWI or DUI in Fort Worth, Arlington, Mansfield or in the surrounding cities of Tarrant County, you were likely asked to take the Horizontal Gaze Nystagmus Test. Nystagmus is a term that specifically refers to the bouncing or involuntary jerking of the eye as it moves from side to side. Generally, alcohol has been determined to cause two types of nystagmus: positional alcohol nystagmus and alcohol gaze nystagmus. As you consume alcohol and become intoxicated, the alcohol will enhance your naturally occurring nystagmus making it visible to the naked eye.

The Horizontal Gaze Nystagmus test, or the pen test, is a test where the police officer holds a pen, or stimulus, 12 to 15 inches away from your eyes and moves the pen back and forth. As the officer moves the pen back and forth, he is observing your eyes tracking back and forth and looking for an involuntary jerking of your eyes. As the police officer administers the HGN test, he will be looking for three specific “clues” per eye that will allow him to mark you as failing the HGN test: lack of smooth pursuit of your eyes, distinct and sustained nystagmus at maximum deviation and the onset of nystagmus prior to 45 degrees. The HGN Scoring Sheet provides that there is a maximum score of 3 clues per eye, for a total of 6 possible clues. According to NHTSA, if you scored at least 4 or more clues, there is a 77% chance that your blood alcohol content (BAC) was .08 or higher at the time of the test.

Additionally, if you have been charged with a DWI based upon intoxication by a drug, the HGN test can be used as evidence of your intoxication if the drug you ingested was a central nervous system depressant.

Did My Police Officer Correctly Administer the HGN Test?

Although police officers in Fort Worth, Arlington, Mansfield and in the surrounding cities of Tarrant County rely upon the HGN in determining whether or not you were intoxicated at the time of your arrest, it is critical to determine if the police officer properly administered the test – as required by NHTSA. For instance, the police officer must administer the test in an environment in which your eyes could have been clearly seen. If the officer positioned you facing the blinking lights of the police patrol car or in the headlights of the oncoming traffic, the officer may have caused you to show optokinetic nystagmus, a form of nystagmus NOT caused by alcohol.

Additionally, NHTSA clearly states that in order for the HGN and other standardized field sobriety tests to be reliable, they must be administered strictly adhering to the guidelines recommended by NHTSA. The standardized field sobriety tests have been given certain percentages by NHTSA for their reliability. However, if your police officer failed to strictly follow the guidelines as required by NHTSA, the HGN and other field sobriety tests will be determined to be unreliable and may be excluded from evidence for the jury to consider.

Call The Hampton Law Firm now to schedule a free consultation and determine if your field sobriety testing was done in accordance with the NHTSA guidelines.