Horizontal Gaze Nystagmus Test
The Horizontal Gaze Nystagmus (HGN) test is one of three standardized field sobriety tests (SFSTs) validated by the National Highway Traffic Safety Administration (NHTSA) to help determine whether a driver is under the unlawful influence of alcohol. It is also a test that police frequently administer during traffic stops when intoxicated driving is suspected. However, the NHTSA recognizes the HGN as a test that can indicate impairment. In Maryland, it is only admissible to suggest a person has some alcohol in their system.
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 their hands to the side, and keep their 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 technical in their application. Proper administration involves specific requirements on the 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 measures involuntary eye jerking, known as nystagmus. A driver with a high blood alcohol concentration may exhibit involuntary eye jerking as the driver gazes toward the side while following the stimulus.
Police look for three significant clues while administering the HGN test. Each eye is assessed for these three clues, so there are six possible indicators of alcohol. If the officer determines three clues exist, it is supposed to indicate the driver has alcohol in their system.
1. Clue 1 involves the onset of nystagmus in either eye before 45 degrees.
2. Clue 2 involves nystagmus in either eye when the eye gazes as far as possible to the right or left – in this case; there is a sustained and distinct jerking.
3. Clue 3 occurs when the driver cannot follow the stimulus, which is known as a lack of smooth pursuit.
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. In comparison, moving the stimulus from the eye to the driver's shoulder takes four seconds to determine the onset of nystagmus before 45 degrees.
Challenging the HGN Test
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 but related to the driver or the environment.
Common Challenges to the HGN Test
- Unreliable based on police officer's subjective estimations and preconceived notions.
- Unreliable based on the 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
- Driver's pre-existing health issues or medications, like ear disorders, eye disorders, head injury or brain damage, excessive caffeine, antihistamines, barbiturates, illness like the flu or vertigo
Remember that there are over 38 non-alcohol-related causes for nystagmus, and each of these can lead to a failed HGN test!
The HGN test is faulty. An experienced DUI/DWI defense attorney can highlight these weaknesses and create reasonable doubt in the prosecution's case against you.
Contact C. Thomas Brown, DUI/DWI Defense Attorney
Field sobriety tests are a way police officers gather probable cause to arrest you for DUI charges. However, given their subjective nature, these tests are rarely conducted in accordance with regulations and are faulty.
C. Thomas Brown and Tina Harris know how to prepare and challenge field sobriety tests like the HGN. To learn more about how we can help your DUI/DWI case, fill out the online form or call us at 410-398-3850 to schedule a Consultation.