Attacking The HGN Test In A DWI Case

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Horizontal Gaze NystagmusIn both test and refusal DWI cases, the field sobriety tests are an important component of the prosecutor’s case. In test cases, the FSTs usually establish probable cause for the arrest, a rather low standard which is somewhere between an evidence-based gut feeling and beyond a reasonable doubt. The FSTs are much more critical in refusal cases. Typically, they constitute the best evidence of intoxication that the prosecutor can present, and in many cases, the FSTs are the only evidence of intoxication that the prosecutor can use to sway jurors.

The National Highway Traffic Safety Administration only recognizes these three tests as scientifically sound. Peace officers in the Houston area often administer other tests as well, but at best, their results are usually only admissible for limited purposes.

Unlike the other two FSTs, which we’ll examine in subsequent posts, the Horizontal Gaze Nystagmus test is very objective. Either the minimum number of intoxication clues are present or they are absent. For this reason, the HGN is often the first test in the three-test battery, and if the defendant passes this test or only fails it marginally, officers arguably do not have probable cause to proceed with the other two.

Horizontal Gaze Nystagmus

Nystagmus is an involuntary eye tremor that occurs when people track moving objects with their eyes and do not move their heads. Generally, the officer uses a small flashlight, the tip of a pen, or the tip of his/her index finger.

Even under ideal conditions, the HGN test is only about 85 percent reliable. Under less than ideal conditions, reliability is even lower. Usually, when officers administer these tests in the field, it is dark, bright overhead lights are flashing nearby, and a super-bright “take down” light may be on the defendant almost like a spotlight. These conditions are anything but controlled.

Overall, the test is largely inaccurate because a wide range of conditions and substances cause nystagmus other than alcohol. Some of them include:

  • Recent head injury,
  • Some ear disorders,
  • Alcohol Withdrawal Syndrome,
  • A neurological birth injury or genetic condition,
  • Milk, meat, whole grains, and almost any other food with a high Vitamin B1 level,
  • Family history, and
  • Certain medications, like Dilantin.

Most defendants have at least one of these nystagmus-causing conditions.

Another issue with this test, albeit a less common one, is the officer’s qualification. The officer does not need to be a doctor, but the officer must be current on the minimum foundational and continuing education requirements. If the officer fails to qualify, the judge may throw out the test results. Usually, a DWI defense attorney will take the witness on voir dire and ask a series of questions in this area.

Count On an Aggressive Attorney

The HGN may be the pillar of the FST battery, and it’s also a deeply flawed test. For a free consultation with an experienced criminal defense lawyer in Houston, contact the Law Office of Jim Medley.

Written by

Jim Medley

For more than 20 years, attorney Jim Medley has perfected his craft in the field of criminal justice. He garnered extensive knowledge during his 12 years as a police officer in Texas, and applied that knowledge during his time as a professor of criminal law and criminal justice. Mr. Medley brings a unique skill set to the table, and as a result, he would be an invaluable asset in the courtroom should you need DWI or criminal defense in Houston.

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