Horizontal Gaze Nystagmus Test

Horizontal Gaze Nystagmus Test

Nystagmus is a medical term referring to an abnormal and involuntary jerking of the eyeballs. A horizontal gaze nystagmus test is used as a field sobriety test by law enforcement when evaluating someone suspected of driving while drunk. While it’s true that alcoholic beverage consumption can cause nystagmus, so can many medical conditions and medications, including:

  • Inner ear diseases
  • Head trauma
  • Brain tumors
  • Stroke
  • Neurological conditions like multiple sclerosis and Parkinson’s
  • People with albinism or absence of skin and eye pigmentation
  • Certain prescription drugs
  • Genetic causes

The degree of observed involuntary jerking movements and lack of equal pupil size is at least partly subjective and open to interpretation by someone not professionally trained to do so. In fact, a horizontal gaze nystagmus test is only about 77 percent accurate. 

The Horizontal Gaze Nystagmus (HGN) Test and Maximum Deviation

If you’re stopped by law enforcement for suspected drunk driving, the horizontal gaze nystagmus (HGN) test will be performed as follows: 

The officer will tell you to look straight ahead and follow a small object, such as a pen, held at your nose level with equal tracking. The officer will tell you to follow the pen’s movements without moving your head. 

The officer is looking for jerking movements caused by alcohol impairment. A lack of smooth pursuit and equal tracking as the suspect’s eyes move implies that they may be inebriated. You will be told to move your eyeballs at a horizontal gaze as far to the side as they will go.

This is called nystagmus at maximum deviation. If distinct nystagmus is observed four or more times during the test, it’s enough evidence of intoxication and probable cause for a DUI arrest. 

Failing the Horizontal Gaze Nystagmus Test

It’s not surprising to fail a field sobriety test, even if someone is not impaired. The police officer could even be at fault if they:

  • Moved the object too quickly or not at eye level
  • Held the object too close to your eyes
  • Rushed you through the test
  • Didn’t present the testing in a standardized manner

In the case of recent alcoholic beverage consumption, distinct and sustained nystagmus may persist, and oftentimes jerking continues for many hours after the last drink, well after the person is no longer under the influence of the substance and not a danger on the road. 

This is only one example of a false positive horizontal gaze nystagmus test. Even worse, some people have a degree of natural nystagmus. Resting nystagmus may be present in individuals who have had a recent head injury.

Myths about Drunk Driving and Standardized Field Sobriety Tests

  • Sucking on a penny before blowing into the breathalyzer will trick it into saying you’re sober when you’re not. This persistent, nonsensical urban legend is patently false. The test measures air pulled up from deep in your lungs, not your mouth. Moreover, officers will check your mouth before you blow into the machine.
  • Drinking coffee or taking a cold shower will sober you up faster. This is also false. While doing these things may help you feel more alert, your BAC will remain the same until your body can metabolize the toxins. 
  • Careful drivers don’t get stopped by law enforcement. DUI checkpoints could be anywhere, and law enforcement knows what to look for. If you’re driving under the influence of even small amounts of alcohol, you may be stopped and arrested if you fail sobriety field tests. 

How to Choose the Best DUI Attorney

If you’ve been arrested for DUI, especially if it involves a failed horizontal gaze nystagmus test, you should seek legal counsel immediately. A skilled DUI attorney can fight the horizontal gaze nystagmus test results based on their unreliability.

You will need an aggressive defense to protect your license and perhaps even your freedom if an officer claims that you weren’t capable of following instructions and there was a lack of smooth pursuit of eye tracking during the nystagmus test. 

When choosing an attorney to defend you on a DUI charge, these are some qualifications to look for:

  • Membership in either the DUI Defense Lawyers Association or the National College for DUI Defense
  • Recognition in the practice field of DUI and DWI
  • Proven track record of successful prior DUI defense cases
  • Training and certification in field sobriety testing
  • Knowledge of and training in police use of RADAR and LIDAR. LIDAR stands for light detection and ranging
  • Knowledge of the type of blood alcohol detection machine, such as the breathalyzer, used at the time of the arrest

Choosing the Right Defense Is Important

Most of the time, your case outcome will depend on your lawyer’s skill and experience, how well or poorly you performed on your horizontal gaze nystagmus or field sobriety tests, and the scientific evidence of nystagmus at maximum deviation presented by the officer during the arrest.