HGN - Are Police Officers Really Reporting What They See or What They Think Will Get a Conviction

You may have heard of the police doing the "pen test" or "eye test."  What they are referring to is theHorizontal Gaze Nystagmus (HGN) test.  DWI police officers will tell you this HGN test is one of the standardized field sobriety tests they use to determine if you are driving while intoxicated.  

So what is HGN?  The test in essence is a measurement of the movement of the eyes.  Nystagmus refers to the involuntary jerking of the eyes back and forth.  Horizontal refers to the officer moving a pen or other object horizontally across your field of vision.

DWI officers claim that they are looking for three clues in each eye during this HGN test. 

The first part of the test is to determine if a DWI suspect's eyes are able to pursue smoothly - is there jerking in the movement of the eyes.  The next part of the test is to determine if there is nystagmus at maximum deviation - when the pen is held with your eyes as far out as they can go, is there nystgamus.  Finally, the officers are looking to see when the nystagmus occurs as they move the pen across your field of vision.  They are to mark off if they see nystagmus prior to a 45 degree angle.  Each eye is suppose to be checked twice for each of the 3 clues.  The total maximum number of clues for the test is 6.

What the cops don't normally tell you is that there are over 40 types of nystagmus that can naturally occur in an individual.  They also don't tell you that they can't differentiate these other 40+ types of nystagmus and they have not heard of most of the other types of nystagmus.  

According to the federal standards for the HGN, the officers are suppose to use objective criteria for administering the test and scoring the test.  More often than not, however, the officers simply just report that the DWI suspect has 6 of a possible 6 clues on the test.

As Houston DWI lawyers, we have seen hundreds of videos where the police perform the HGN.  Many of the officers that perform the test either do not know how to properly perform the test or choose not to do the test correctly which leads to falsely reporting results on this test.  I have yet to see an officer ask a client if he or she has naturally occurring nystagmus.

If you have been arrested for DWI, ask your lawyer how many clues the cop says you had on the HGN.  My bet is the answer you will get is 6 of 6.  What is your score on the HGN?

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Hunter Biederman - November 18, 2009 5:14 PM

So True. We had a client that had a glass eye. Number of clues, 6. Really?!?!

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