Horizontal Gaze Nystagmus (HGN) Test: DUI Field Sobriety Tests
The Horizontal Gaze Nystagmus test provides the most possible ground for challenge among the field sobriety tests. That's because some DUI courts have ruled that it's a scientific test, which requires the state to show that the officer is qualified to interpret the test and testify to the results.
However, these legal findings haven't stopped police in many jurisdictions from including the HGN as part of the field sobriety tests that are administered to DUI suspects.
If you've been arrested for DUI and failed the Horizontal Gaze test, you can learn about your options for fighting the DUI charge and how to protect your legal rights by speaking with a DUI attorney in your area:
What is the Horizontal Gaze Nystagmus Test?
The Horizontal Gaze Nystagmus Test is designed to test the brain's ability to control the eye muscles. When a person has been drinking or is under the influence of chemical depressants, the brain's ability to smoothly control eye muscles suffers. The result is a jerking motion of the eye when a person look from side to side.
When a police officer is performing this field sobriety test, the suspect must keep his or her head still and follow the object with only his or her eyes, focusing on the object until told to stop. Testing procedures require that the officer:
- Hold the stimulus 12-15 inches from the suspect's nose and slightly above eye level
- Move the stimulus smoothly across the suspect's entire field of vision
- Check to see if the eyes are tracking together and if both pupils are the same size
- Start with the left eye, moving the stimulus to the right so it takes 2 seconds to bring the suspect's eye as far to the side as it can and repeat from right to left
- Check at least twice for each of the three clues in each eye:
- Lack of smooth pursuit
- Distinct nystagmus (no white is showing on the side) when the eye is to the outside of field of vision for 4 seconds
- Onset of nystagmus before the eye has moved 45 degrees
The HGN test is only one kind of field sobriety test that an officer will typically ask a DUI suspect to perform as part of a DUI stop. Often it is the combined results of all of these tests that will lead an offer to arrest a suspect or allow them to continue driving.