The Horizontal Gaze Nystagmus Test

Learn about the Horizontal Gaze Nystagmus test and how it can impact your case. Trust Philip Kim Law, P.C., for expert legal guidance. Call us today for help.

Author: Philip Kim, Founder, Philip Kim Law, P.C.

Defense lawyer Philip Kim has committed his career to standing up for the accused, and protecting the rights and reputations of his valued clients. If you face criminal charges in Georgia, we can provide you with the skilled, effective defense representation you need.

Published on October 11, 2023.


Horizontal Gaze Nystagmus (HGN) Test

Normal eye movements during everyday activities, such as driving, include smooth pursuit, fixation, and saccade. Smooth pursuit involves maintaining eye position on an object when there is motion between the observer and the object.

Fixation refers to stable maintenance of eye position when there is no relative motion between the observer and the object. Saccades are fast-scanning eye movements.

Nystagmus describes an eye undergoing a repetitive back-and-forth movement. Horizontal gaze nystagmus occurs when the eyes move and jerk involuntarily from side to side.

When you are with HGN, you cannot focus directly on a single object because of the involuntary jerking of your eyes. Being drunk may make you experience an impairment accompanied by Horizontal Gaze Nystagmus (HGN).

HGN is often associated with the consumption of a significant amount of alcohol. Excess amounts of alcohol can make your nervous system lose control of eye movements. So, law enforcement officers carry out the HGN test when they suspect you of DUI.

Other intoxication signs like vomiting, slurred speech, and confusion may accompany HGN.

How Does the HGN Test Work?

The HGN test is one of the divided attention tests conducted by police officers. It is a standardized field sobriety test that law enforcement officers often administer to determine whether you are under the influence of alcohol. When you fail this test, they can proceed with a DUI arrest. There are two other standardized field sobriety tests, namely:

  • The walk and turn test.

  • The one-leg stand test

Several scientific studies have linked these three tests to a DUI impairment. Yet, officers also rely on non-standardized field sobriety tests in their DUI investigations. These non-standardized field tests include:

  • finger count test

  • hand pat test

  • The Rhomberg balance test

  • vertical nystagmus

  • the finger test

Why Do the Police Use HGN?

The police make use of HGN during a DUI arrest. The purpose of carrying out this test is to determine whether or not you are driving under the influence. Note that the NHTSA manual used to train police officers has instructions on this test.

They watch out for three essential intoxication clues in each of your eyes during the test. A point is awarded to each of the clues spotted during the pendency of the trial. Scoring four or more points out of the total of six points will make an officer arrest you for DUI. With these points, the officers would classify your Blood Alcohol Concentration as above 0.10 per cent, as stipulated by NHTSA.

How Police Conduct the HGN Test

The police must administer the HGN test in a way that ensures your eye visibility. This factor can be established by using a well-lit area or using a flashlight to illuminate your face. It would be best to avoid facing the flashlight of passing cars so your attention wouldn’t be divided.

The officers must qualify you before the test by ensuring that your eyes have equal tracking and pupil size. The officer is not meant to carry out the HGN test where any of these qualifications are missing.

However, the HGN test can be conducted on you if you qualify. First, the officer must notify you that they want to check your eyes and instruct you to keep your head still while following the stimulus with your eyes only. They will order you to keep following the stimulus until you are ordered to stop.

After that, they must position the stimulus approximately 12 to 15 inches from your nose and slightly above your eye level.

Three clues are assessed to signify intoxication in the HGN test:

  • Absence of smooth pursuit

    The officer must move the stimulus from your left eye to your right. This action moves your vision as far to the side as it can go while the officer examines whether your left eye pursues the movement smoothly. The exact process is then repeated to test your right eye whether or not it pursues smoothly.

  • Distinct and sustained nystagmus at maximum deviation

    After checking for the absence of smooth pursuit, the officer will check for distinct nystagmus at maximum deviation starting from your left eye. The officer will move the stimulus towards your left side until your vision goes as far to the side as possible. The officer will hold your eye at that position for at least four seconds. What they look out for is any slight jerking of your eye. When you are impaired by alcohol, the jerking will be very pronounced.

  • Onset of nystagmus prior to 45 degrees

    The next clue to check for is the onset of nystagmus prior to 45 degrees. The officer will move the stimulus approximately four seconds toward your right shoulder. Then, they watch out for a jerking before the stimulus is 45 degrees from your face centre. The same procedure is then repeated for your left eye.

Other Types of Nystagmus

There are two other types of nystagmus aside from HGM, including:

  • Jerk nystagmus

  • Pendular nystagmus

Nystagmus condition can be acquired or inherited by birth. Acquired nystagmus can occur due to alcohol consumption, injury, drug use, or neurological disorders. On the contrary, congenital nystagmus happens at conception. Such judgments are difficult for an officer to make accurately under roadside conditions.

Accuracy of the HGN Test

The National Highway Transportation Safety Administration (NHTSA) revealed that the HGN is 77% reliable in determining blood alcohol concentration. This rate shows that approximately one out of four HGN test results may be inaccurate. The inaccuracy can be due to inadequate officers’ training.

What Are Some Alternatives to the HGN Test in Dui Cases?

The officers use not only the HGN test in DUI cases. They conduct chemical tests to determine your Blood Alcohol Concentration. These tests are called BAC tests and include blood, urine and breath tests.

Philip Kim Law, P.C. Can Help You

To help you determine whether your HGN test was administered correctly and for your DUI less safe, reach out to us at Philip Kim Law, P.C. Our experienced DUI attorneys can help you identify whether the conducted HGN test incorrectly and build a strong defense.

Trust us for legal guidance. Contact us today for a free consultation with questions on HGN test results.

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