Is The Truth in the Eyes?

A Brief on Horizontal Gaze Nystagmus in Vermont DUI Investigations

What is Horizontal Gaze Nystagmus (HGN)?

The definition of nystagmus is a “rapid involuntary movement of the eyes.” This could be side to side, up and down, or circular movements of the eyes. This is due to brain disease or inner ear balance. Brain disease causes vertical nystagmus, while inner ear balance causes horizontal. 

Alcohol consumption, as well as other depressants and various types of drugs can also lead to nystagmus via preventing the brain from properly communicating with the eyes, causing horizontal nystagmus. The further the individual becomes impaired, the more violent the eyes will jerk. 

How Do Vermont Law Enforcement Use HGN?

The HGN test is one of the three parts of the Standard Field Sobriety Tests System. Criminal justice students in Vermont are taught that the HGN test is the most reliable field sobriety test.

Officers in Vermont administer the test in three parts. They always begin with the left eye. The first thing that they test for is smoothness in movement. As the eye moves from side to side following the object that it is prompted to follow, does it move smoothly or jerk? The next thing tested for is nystagmus at the end of the movement. When the eyes are moved all the way to one side and held in position for four seconds do they begin to jerk at all? Finally, They test to see if the eyes begin to jerk before they reach 45 degrees in movement. 

For each eye, there are 3 points allotted in the test, totalling 6 points. Officers are taught that if the suspect fails 4 or more of these points, they can tell with 77% certainty that their blood alcohol percentage is above 0.10%. 

How You May Limit the Relevance of HGN in a VT DUI Trial

Before an officer may go ahead with an HGN test, they must verify that the subject’s eyes track stimulus together, and that their pupils are the same size. If they are not, this could be a sign of medical disorder or head injury. 

If your case goes to trial, it is important for your attorney to file a motion in limine to exclude all evidence regarding the HGN test. This is essentially a motion to exclude certain evidence from being presented to a jury as it is irrelevant, untrustworthy, or more based on prejudice than probate. 

Additionally, the state should not be allowed, based on legal precedent, to enter an HGN test into evidence if they have not given notice of an expert witness testimony on the subject. If the evidence were allowed to be presented in court, the witness should be required to relate the complicated science behind the test to the jury, who’s members most likely don’t have advanced scientific backgrounds. Vermont trial courts have decided that this expert testimony must occur before HGN evidence is allowed to be brought forward to the jury.

However, the state rarely has the time, resources, or will to pay for an expert witness sufficient enough to allow for HGN evidence to be used in trial. A motion in limine will most likely be successful in blocking this test from following you into the courtroom. It is of the utmost importance that you contact your attorney as soon as you receive the citation, as they can help prevent you from loss or suspension of licensure, large fines or possibly jail time. Preventing HGN evidence from being used in your trial could just make the difference.