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HGN Eye Test

A commonly administered standard field sobriety test (SFST) sued during DUI investigations in the Chicago metro area is the Horizontal Gaze Nystagmus (HGN) test. Police officers perform this test on a regular basis under the presumption it may indicate whether a person is illegally intoxicated or not by alcohol or drugs to operate a motor vehicle.

When a traffic stop is conducted and the police suspect you are operating the vehicle under the influence of alcohol or drugs, the officer may first ask you to perform the HGN test before asking you to provide a breath sample. Keep in mind that you are allowed to refuse this test. It and the other standard field sobriety tests are not based on sound science but are riddled with problems and susceptible to human error.

At Dolci & Weiland, we recognize and have a thorough understanding of HGN eye tests. We know their faults and vulnerabilities. We know what to look for. And we know how to challenge the results of these tests before a judge and jury. Contact us today to learn more about our approach to DWI defense in the greater Chicago metro area.

What is the Horizontal Gaze Nystagmus Test?

The HGN test is a standard field sobriety test that focuses on the involuntary jerking (nystagmus) of the eye. The eye involuntarily jerks naturally when a person's gaze goes off to the side. For an impaired person, the natural nystagmus is allegedly exaggerated. This, of course, is subjective because what is "normal" jerking for one person may not be the same for another person. As such, this test is fundamentally flawed from the start. 

But to be administered properly, specific instructions must be provided. 


To administer the HGN test, the officer should tell the person to follow an object with his or her eyes slowly, back and forth. The officer may use his finger, a pen, or another similar object. As you follow the object, the officer looks for the "jerking". The officer is supposed to look for three specific cues when a person conducts this field sobriety test:

  1. the alleged DUI offender performing the test is unable to follow a moving object smoothly;
  2. there is distinct eye jerking when the eye is at maximum deviation; and
  3. the eye jerks within 45 degrees of the center.

The administrative procedures according to the National Highway Traffic Safety Administration (NHTSA) are as follows:

  • Check for eyeglasses.
  • Provide verbal instructions.
  • Position stimulus (12-15 inches and slightly above eye level).
  • Check for
    • equal pupil size and resting nystagmus
    • equal tracking
    • lack of smooth pursuit
    • distinct and sustained nystagmus at maximum deviation
    • onset of nystagmus prior to 45 degrees.
  • Total the clues.
  • Check for vertical nystagmus.


To "score" the HGN test, there are six clues (three clues per each eye). If the person performing the test scores four or more points, then the police can assume that the person has a blood alcohol content (BAC) of .8 percent or more, which is the illegal intoxication level for operating a motor vehicle.

The three clues per each eye are:

  1. the lack of smooth pursuit, meaning the right, left, or both eyes jerked or bounced as they followed the officer's finger, pen, or another object – the officer, however must not have jerked his finger, pen, or another object while administering the test;
  2. distinct and sustained nystagmus at maximum deviation, meaning that while the right or left eye is held at maximum deviation, the left, right, or both eyes jerk or bound for a minimum of four seconds and continues to do so toward the side; and
  3. the onset of nystagmus prior to 45 degrees, meaning the left, right, or both eyes start to jerk before 45 degrees.

How can the Horizontal Gaze Nystagmus Test be challenged successfully in an Illinois DUI case?

The HGN test is only one of three standard field sobriety tests, and of the three, the HGN test is the most accurate. According to NHTSA and a study released in 2007 (The Robustness of the Horizontal Gaze Nystagmus Test), the test is able to accurately determine illegal intoxication 88% of the time. That may sound high, but that also means 12% of those arrested due to failure to perform this test may not have been intoxicated. And the arrest alone on DUI charges is enough to cause problems for a person financially, emotionally, socially, and professionally. 

Fortunately, the HGN test can be challenged by a strategic DUI defense attorney who understands the test and its extensive flaws.

Unscientific Testing

Like all field sobriety testing, the fundamental problem of the HGN test is its unscientific foundation. There are no medical professionals conducting the test and the test alone assumes that alcohol is the only cause for a nystagmus when, in fact, there are approximately 40 medical conditions that can cause a nystagmus.

Examples of other causes of a nystagmus include:

  • Medications
  • Thiamine deficiency
  • Stroke
  • Trauma
  • Tumor
  • Multiple Sclerosis
  • Cataracts
  • Albinism
  • Meniere's disease
  • a family history of nystagmus.

Improper Administration

The police must be certified to administer the HGN test. But even then, the training is at best questionable and most police officers may not even understand what parts of the test mean, particularly understanding what "onset of nystagmus prior to 45 degrees."

In fact, according to the Robustness of the Horizontal Gaze Nystagmus Test, there is a 61.1% error rate. Most of these errors are attributed to the officer holding the stimulus (a pen or another object for the test-taker to follow with his or her eyes) to high. Many officers, too,  fail to hold the test-taker's attention long enough – the officer is supposed to hold the stimulus for a minimum of 4 seconds to confirm a sustained and distinct nystagmus at maximum deviation, but this often doesn't happen and can contribute one to two points towards the test-taker's total score.

Contact an Experienced DUI Attorney Serving DuPage & Cook Counties

If you failed an HGN test during a traffic stop, you may get arrested for a DUI. Never plead guilty, but seek the help of experienced DUI defense attorneys. At Dolci & Weiland, we know field sobriety tests and their flaws, and we know how to successfully challenge them before a judge and jury. If you live in the greater Chicago metro area, contact our office today to learn more.