Vertical Gaze Nystagmus in DUI cases - DUI Attorney
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Vertical Gaze Nystagmus in DUI cases

Vertical Gaze Nystagmus

Another Flawed Way of Measuring Impairment

The vertical gaze nystagmus (VGN) is similar to the HGN except instead of the officer moving his stimulus back and forth across your face to track your eye movement, he moves it up and down in a vertical manner.  When an officer receives training for HGN in the field and during his time at the police academy, he is also taught how to administer the VGN.


Like the HGN, VGN attempts to measure how your eyes respond when asked to follow the movement of a stimulus.  The officer is looking to see whether your eyes can follow smoothly, or whether there is a small involuntary jerking that occurs.  If your eyes cannot follow smoothly, it is argued that you may be impaired. 

The problem here is that impairment by drugs or alcohol is not the only thing that can cause this jerking to occur.  The officer is also looking for other things, called “angle of onset” and “distinct nystagmus at maximum deviation.”  These “official” names sound like complex measurements, but they are not.  Especially when they are done by inexperienced and unqualified police officers in less then optimal conditions in the field.

Officers are told that failure to perform VGN successfully indicates not a specific level of BAC, but rather a very very high amount of BAC.  “Very very high amount” sounds real scientific, huh?  Not! There is no way to prove from VGN what your exact BAC level is, and there is no way to show, without chemical test confirmation, that the BAC is particularly high either.

VGN is no longer as admissible as it used to be, and it is not one of the three sobriety exercises that is encouraged by NHTSA. That does not mean you will not be given it, however, or that your results won’t be used against you.

More Non-Standardized Field Sobriety Tests

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