Horizontal Gaze Nystagmus (HGN)

Imagine driving late at night, bad part of town, alone, and all of the sudden, flashing blue and red lights are behind you. You pull over, you’re nervous (who likes this type of hassle, especially late at night?). Now the cop behind you turns on several more spotlights, and asks if you’ve been drinking. “Yes, two beers”, the worst, but most common response, to which the officer requests submission to a few “Field Sobriety Tests“. Now, I know what you’re thinking, it’s late, bad part of town, and traffic is wizzing by, but somehow, in the midst of all this, the officer wants you to stand on one leg, walk a straight line, watch his pen move your eyes side to side, or put your finger to your nose several times. (Please don’t tell the officer that you couldn’t even do these tests when you are sober!)

Field Sobriety Tests (FST’s) are some of the most unreliable means to determine intoxication ever invented. Believe it or not, the same tests are given to a 21 year old college athlete as are given to a 65 year old woman using a walker! Think back to middle school gym class, remember some of the kids could do the balance beam and various gymnastics, others couldn’t! Even at an early age, differences in balance and athletic ability begin to emerge, and typically get worse with age. Law enforcement’s goal for FST’s is to gather evidence to be used against you later, and gather enough probable cause to arrest you. (Their evidence gathering didn’t start there, they’re watching your every move–did you use the car door as a crutch to exit the car? Struggle to find your car’s registration? etc. etc.)

Many years ago, several Central Florida law enforcement agencies (Orange County Sheriff’s Office comes to mind) had a special video room to conduct FST’s, and in car video cameras to capture the moment. All that has, for the most part, been cancelled in Orange County, though Brevard County and a few others still retain in-car video. As a person arrested for DUI, you typically WANT a video of the incident, because an arrestee is almost never as drunk as alleged in the officer’s bias written report. Even security camera footage that captures the FST’s can aid in defending a DUI accusation. Be sure to contact criminal attorney John Guidry as soon after arrest as possible, because security camera footage (and all sorts of other evidence) fades away as time marches on….

There are several Field Sobriety Tests out there, the “finger to nose”, “Counting backwards from 100”, “Romberg Balance test”, “HGN”, “one leg stand”, “walk and turn”, and more. All of the above tests seek to divide a driver’s attention to two tasks, as studies have shown that with alcohol impairment, the brain has difficulty computing multiple tasks under such conditions (walk a straight line and touch heel to toe–walk and turn test). Our big government spent money back in the late ’70’s to test these exercises, and the United States Department of Transportation determined that three tests worked best. These are the Horizontal Gaze Nystagmus (HGN), Walk and Turn, and One Leg Stand.

The Horizontal Gaze Nystagmus (HGN) test seeks to discover an involuntary jerking of the eyeball that can be aggravated by drugs or alcohol. The officer does this by having a suspect’s eyes follow a stimulus (usually a pen) while he looks for involuntary jerking of the eye motion. The DUI suspect is completely unaware of the eye jerking because this eye behavior does not effect vision. It is claimed that alcohol impairs the eye’s smooth pursuit, and this is noticable at certain angles. However, caffeine, nicotine, or asprin also cause nystagmus that is virtually identical to that caused by alcohol impairment (See “Horizontal Gaze Nystagmus: Voodoo Science”, by Pangman, 2 DWI J. 1, 3-4 (1987)). Furthermore, fatigue causes nystagmus, with a strong effect at the end-position of the test (when the officer has you looking to the far left or far right), and most people have the onset of nystagmus near the end-position of the test anyway due to eye muscle fatigue and strain.

So, how much alcohol causes jerky eye movement, or nystagmus? Studies have shown that a lack of ‘smooth pursuit’ begins at .04 BAC, but whether or not a person’s blood alcohol level is rising or falling greatly affects the HGN test, with nystagmus persisting even after the BAL is at zero! Here’s a brief rundown of how this test is conducted:

First, the officer is instructed to have the suspect remove their glasses, put their feet together, hands at their sides, keeping the head still, have the suspect follow the stimulus with their eyes only, positioning the stimulus approximately 12 inches from the nose at slightly above eye level,Next, watch the eyes for lack of smooth pursuit, always beginning with the suspect’s left eye, taking two seconds to move the eye as far to the side as possible, and two seconds back, repeating this twice in each eye, holding the eye at the far side for at least four seconds,Finally, move the stimulus slower, this time four seconds to complete each way, watching for nystagmus prior to 45 degrees.

Once the officer has completed the above, a determination of impairment can be made based on clues from either a lack of smooth pursuit, nystagmus at maximum deviation, or the onset of nystagmus prior to 45 degrees.

That depends. HGN test results are admissible upon a showing by the State the HGN’s reliability, the qualifications of the person conducting the test, and the meaning of the results. This ‘foundation’ includes a description of the officer’s training, education, and experience in administering the test and a showing that the test was administered properly. The foundation may not include any discussion regarding the accuracy with which HGN test results correlate to, or predict, a BAC greater or less than .08%. Keep in mind that the reliability of these tests were determined in controlled, research settings, thus our ability to determine their effectiveness in an uncontrolled setting (the side of the road, late at night,in a parking lot) is severely diminished, as it becomes difficult to evaluate a poor perfomance in light of nervousness, distractions from passing cars or spectators, weather conditions, medical problems (alcohol!).