Wednesday, April 3, 2013

A Primer on a Misunderstood Field Sobriety Test

Of the three standardized field sobriety tests - the Horizontal Gauze Nystagmus (HGN) is the one least understood by clients who've been arrested for DUI in Illinois.

Unlike the One Leg Stand Test and the Walk and Turn Test, the HGN test,  does not have anything to do with coordination and little to do with instructions (although the failure to follow the instruction to "keep one's head still" is frequently cited by prosecutors as evidence of impairment).

Nystagmus is an uncontrollable tremor of the eye. All people have some nystagmus but intoxication causes it to become more readily observable in most people. The HGN test involves an officer holding a stimulus (a finger or a pen) in front of the driver's face while watching the driver's eyes. Before the HGN test begins the officer looks for nystagmus while the eyes are resting. If the officer sees resting nystagmus the HGN test is not to be relied upon.

To begin the test, the officer has the driver hold their head still while following the stimulus with their eyes. The officer smoothly and slowly moves the pen or finger back and forth across the driver's face and slightly above their eye line. First the officer looks to see whether the driver's eyes smoothly track the stimulus, then the officer sees whether the driver's eyes quiver while focusing on the extreme left and right, and finally the officer looks for nystagmus when the eyes focus on the stimulus at less than a 45 degree angle.

According to the National Highway Traffic Safety Administration (NHTSA), the HGN is failed if the officer observes nystagmus in both eyes under at least two of the three conditions (e.g. eyes do not track smoothly and nystagmus at the extreme left or right).

However, a driver may exhibit nystagmus for several reasons other than intoxication, including medical conditions and officer error.  For example, if the officer holds the stimulus too high it can create nystagmus. If the officer moves the pen too quickly back and forth it can cause nystagmus. If the test is administered in a location where there are quickly moving objects within the driver's field of view (e.g. cars on the freeway) it may cause nystagmus. If an officer performs the HGN test repeatedly or takes too much time performing the test, the driver's eyes may become fatigued and exhibit nystagmus.

Because the questionable correlation between intoxication and nystagmus many Illinois judges do not give great weight to HGN tests in a DUI trial. However, if you were given the HGN test make sure to talk to an attorney to determine whether the test was administered accurately and whether it may be used at trial, or in a hearing to rescind Statutory Summary Suspension.

If you or a loved one has been charged with a DUI or would like more information on what to do if pulled over for a DUI, please contact the Law Offices of Brent M. Christensen please send us an e-mail or call 630-510-3252.


  1. It's really helpful to know how that test works and what the common issues are with it. I didn't realize that that's the most common test used for field sobriety to convict people of a DUI. My brother was just charged last night, and we're not really sure if he has a case. It's probably smart for him to contact an attorney to make sure that the tests were done right. It's possible that a lawyer could help him about a bit with that.

  2. Nice post! I am really in love with your blog thank you so0o much. H. Kim Doniger

  3. Nice post! DUI is much more than a offence in USA. This ticket imparts major effects on your routine life. You will need best DUI lawyer in order to deal with the DUI case.

  4. Nice Post :) DUI is really a major offense in USA. The only way to get out of DUI's trap is Best DUI Lawyer .