What is the HGN test?

The HGN test is the eye test police use to see if a driver is DWI. This is because alcohol causes a driver’s eyes to involuntarily bounce or jerk around. This bouncing or jerking is called nystagmus. Consequently, police look for this clue as the driver’s eyes move from side to side. NHTSA calls this the horizontal gaze nystagmus test. Or the HGN test for short.

Of major interest, the HGN test along with the One-Leg-Stand (OLS) and Walk-and-Turn (WNT) tests are the three tests police use to decide if they should arrest a driver for DWI. These three tests along with either the breath test or blood draw are the key pieces of evidence in a DWI trial. Critically, juries use these pieces of evidence to decide if a driver is guilty or not of DWI.

But what specific clues do police look for with the HGN test? Plus, what are the HGN steps police use in a DWI case? And what happens if the police mess up the HGN test? This post will answer these questions. Most important of all, we will show you how to attack an HGN test to help improve your chances in a DWI trial.

What are the HGN clues?

Police look for three clues in each eye during the HGN test. They are:

  1. The eye cannot follow a moving object smoothly. In other words, as the eye moves from the center to the side, it bounces or jerks around;
  2. Nystagmus is marked and sustained when the eye is held at maximum deviation for at least four seconds. This means when the eye is held at the far end of the field of vision, it also bounces or jerks around; and
  3. Nystagmus is visible before the officer’s pen or wand reaches a 45 degree angle.

Above all, there are three clues for each eye. As a result, there are a total of six clues possible in the HGN test. If the officer finds four or more clues during the test, then he will decide the driver is intoxicated.

What are the HGN Test Steps?

Time needed: 2 minutes.

Police must follow the steps below when they give a driver the HGN test. This is because the HGN test is standardized. And if the officer does not follow these steps, it could compromise the results of the test.

  1. Check the suspect for eyeglasses.

    If the driver is wearing eyeglasses, then the officer will ask the driver to take them off.

  2. Police officer gives the driver verbal instructions.

    The officer gives the driver the following instructions:

    Put your feet together.
    Keep your hands at your sides.
    Look at the pen or stimulus.
    Follow the pen or stimulus with your eyes only.
    Keep looking at the stimulus until the test is over.

  3. The officer puts the pen or stimulus in front of the driver.

    Officer places a pen or stimulus about 12-15 inches from the driver’s nose. Also, the pen should be slightly above eye level.

  4. Check for equal pupil size and resting nystagmus.

    The officer makes sure the driver’s eyes have equal pupil size. If the eyes do not have equal pupil size, then it is possible that a medical disorder or injury is causing the nystagmus.

    The officer also checks the driver for resting nystagmus.

  5. Check for equal tracking.

    The officer checks the driver’s eyes for equal tracking. He does this by moving the pen or stimulus smoothly across the driver’s entire field of vision. In particular, he moves the pen to the far right, then to the far left, and back to the center.

    If the driver’s eyes do not track equally, this could mean the driver is hurt, blind, or has a medical disorder.

  6. Clue 1: Lack of smooth pursuit.

    The first clue is a lack of smooth pursuit.

    During this step, the officer moves the pen or stimulus as far to the side as the eye will go. While he is moving the stimulus, the officer is looking at the suspect’s eyes to see if he can follow the stimulus smoothly. If the eye jerks or bounces, then this is a clue the driver is intoxicated.

    Also, the officer must move the stimulus at a speed that takes two seconds out and 2 seconds back for each eye. Finally, he must repeat this procedure for each eye.

  7. Clue 2: Distinct and sustained nystagmus at maximum deviation.

    During this test, the officer moves the pen or stimulus as far to the side as possible. When he gets to the far side, then the officer will hold the pen or stimulus for a minimum of four seconds.

    If the eye bounces or jerks around when it is being held at the far end, then this will be a clue that the driver is intoxicated.

    Like the first clue, the officer must check each eye twice for this second clue.

  8. Clue 3: Onset of nystagmus prior to a 45 degree angle.

    The officer moves the pen or stimulus from the center until it reaches the edge of the driver’s shoulder. It should take four seconds for the pen or stimulus to reach the shoulder. The officer should check each eye for this clue twice.

    If the officer sees the driver’s eye bounce or jerk before it reaches the 45 degree angle, then this will be a clue that the suspect is intoxicated.

  9. Add up the clues.

    There are three clues for each eye for a total of six clues. If the officer sees four or more clues during the HGN test, then the officer will decide the driver is intoxicated.

What happens if police do not follow these steps?

The case law is clear. Police must follow the HGN steps listed above. If police do not do this, then the State cannot use the HGN results against the driver in a DWI trial. If this happened in your case, then your DWI lawyer can challenge the test results under Tex. R. Evid. 702.

Significantly, Rule 702 allows motorists arrested for DWI to challenge the HGN test results. You can do this by filing a motion with the court asking it to see if police followed the HGN steps. If police did not, then the judge should kick out the test results in your case.

DWI Defense.

DWI cases are perhaps the most common crime in San Antonio, Texas. In fact, most people arrested for DWI are first-time offenders. That is, most people arrested for this crime have never been in trouble before. This is their first brush with the law. So the process feels scary.

But DWI cases have three common parts or elements. They are:

  1. The HGN, OLS, and WNT tests;
  2. The breath test or blood draw results; and
  3. Body and dash cam videos.

By breaking a DWI case down into these smaller parts, it does two things. First, it helps take away the fear factor from the case. This is because it puts the case into its proper context. A person facing a DWI charge can see how the smaller parts add up to a DWI conviction. This can help the driver decide if he should plead out or fight the charge.

Second–for those drivers who want to fight their case–breaking the case down helps them target key pieces of evidence. For example, if the police did not do the HGN test the correct way, then you can ask the judge to keep the results out. This is important because HGN test results carry a lot of weight with juries. As a result, kicking out bad HGN tests is an important step in getting a good result at trial.

San Antonio DWI Attorney Genaro R. Cortez.

Questions about your DWI case? Call 210-733-7575 to get a free case consult.