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Understanding DUI Arrests in Florida and the Horizontal Gaze Nystagmus Test

Horizontal Gaze Nystagmus (HGN) test is one of three standardized field sobriety tests (SFSTs) validated by the National Highway Traffic Safety Administration (NHTSA). It is also a test that police in Sarasota, Manatee or Monroe Counties administer frequently during traffic stops when intoxicated driving is suspected. Though the NHTSA recognizes the HGN as a test that can indicate impairment, this test is not fool-proof. In fact, the government's own scientific evidence shows that 77% of all drivers with lawful blood alcohol levels are FALSELY identified by HGN as impaired. 77% false positives!

Hudson Law Office will investigate your case, including the types of and manner in which field sobriety tests like the HGN test were administered. Tom Hudson has been certified as an Instructor in Standardized Field Sobriety Testing since 2004. At Hudson Law Office, we use those skills and resources to ensure you don't get railroaded. Contact us at (941) 358-5400 or (305) 292-8384 to schedule a Free Strategy Session and learn more about how we will help you fight your DUI charge in Sarasota, Manatee or Monroe Counties.

What is a Horizontal Gaze Nystagmus Test?

The Horizontal Gaze Nystagmus test is one of three standardized field sobriety tests used by the police in Florida to help determine whether a driver is under the unlawful influence of alcohol or drugs.

How is the HGN Test Performed?

The officer conducting the HGN test should provide clear verbal instructions to the driver. The police officer should tell the driver to stand still, place hands to the side, and keep head still. Then they must be properly instructed to look at a stimulus, like a pen or another object, and follow it with both eyes while the officer moves the stimulus from right to left.

The officer assesses the driver's eyes while moving the object from side to side. HGN tests, however, are very technical in their application. Proper administration involves specific requirements on distance between the stimulus and the driver's nose (12 - 15 inches), timing and length of holds (hold the stimulus for at least 4 seconds at the maximum deviation), and how many times and ways the stimulus is passed back and forth.

The HGN test is meant to measure the involuntary jerking of the eye – known as nystagmus. A driver with a high blood alcohol concentration may exhibit involuntary jerking of an eye as the driver gazes toward the side while following the stimulus.

Three Major Clues of Intoxication

During the HGN test, the officer will ask the driver to follow a small object, such as a pen or a finger, with their eyes as it moves horizontally from side to side. The officer will look for three specific clues in each eye (for a total of six clues):

  1. Lack of smooth pursuit: The officer will check to see if the driver's eyes are able to smoothly follow the object without jerking or bouncing.
  2. Distinct and sustained nystagmus at maximum deviation: The officer will look for any jerking movements of the eyes when the object is moved as far to the side as possible.
  3. Onset of nystagmus prior to 45 degrees: The officer will check to see if the jerking movements of the eyes begin before the object reaches a 45-degree angle from the center of the driver's face.

If the officer observes four or more clues during the test, it is considered a strong indication of impairment. However, it is important to note that the HGN test is not foolproof and can be affected by a variety of factors, such as medical conditions or fatigue.

Each clue requires specific motions or manners in which the stimulus is held or passed. Each clue also requires different timing. For example, the movement of the stimulus to determine the lack of smooth pursuit should be two seconds out and back to each eye while it is four seconds to move the stimulus from eye to the driver's shoulder to determine the onset of nystagmus prior to 45 degrees.

Ways to Challenge the HGN Test in Florida

HGN tests can be challenged effectively by arguing against their reliability (these tests are highly subjective) or proving improper administration of the test (these tests require following strict and specific technical rules). Also, these tests can be challenged based on matters not associated with the test itself, but matters related to the driver or to the environment.

Common Challenges to the HGN Test

  • Unreliable based on police officer's subjective estimations and preconceived notions
  • Unreliable based on police officer's failure to administer the test properly
  • Unreliable based on external factors

Common External Causes of Failed HGN Tests

  • Bad weather
  • Administered at night in darkness or during the day with a glaring sun
  • Bad roads or other environmental issues
  • Patrol car lights flashing or other lighting issues
  • 60% of the time, police conduct the HGN test with passing traffic in the subject's field of view--a BIG no-no!
  • Driver's pre-existing health issues or medications, like ear disorders, eye disorders, head injury or brain damage, excessive amounts of caffeine, antihistamines, barbiturates, illness like the flu or vertigo

Keep in mind that there are more than 38 non-alcohol-related causes for nystagmus, and each of these can lead to a failed HGN test.

The HGN test is faulty. Your DUI defense attorney can may be able to highlight these weaknesses and create reasonable doubt in the prosecution's case against you. Our DUI defense lawyer will investigate and review the results of your HGN test and challenge it accordingly.

Contact Hudson Law Office in Sarasota, Manatee or Monroe Counties Today

Field sobriety tests are a way police officers gather probable cause to arrest you for DUI charges. These tests, however, are rarely conducted in accordance with regulations and are faulty given their subjective nature.

At Hudson Law Office, we know more about the HGN test than nearly anyone. Tom Hudson delivered an address on HGN to the Summer Session of the National College for DUI Defense at Harvard Law School in 2019. We know how to prepare and challenge field sobriety tests like the HGN test. To learn more about how we can help your DUI case, contact us by filling out the online form or calling us at (941) 358-5400 or (305) 292-8384 to schedule a Free Strategy Session.

Why We're Different

Board Certification as a DUI Specialist by the National College for DUI Defense. Formal NHTSA Certification as an Instructor of the Standardized Field Sobriety Tests given by police in DUI cases. Formal training as a NHTSA Drug Recognition Evaluator. ("Drug Evaluation & Classification") Formal training to operate the Intoxilyzer 8000, Florida's official breath test instrument. Extensive experience in teaching other attorneys how to handle DUI cases. Hundreds of jury trials both as defense lawyer and as prosecutor.