The Horizontal Gaze Nystagmus (HGN) Test is an eye exercise that Nevada police frequently use to determine if a motorist is driving under the influence of alcohol. The results of the test can be a factor in whether you get arrested and charged with DUI.
On this page, our Las Vegas DUI Defense attorneys answer frequently asked questions about the HGN exam in Nevada drunk driving cases. (Click on a question below to go directly to that topic.)
- 1. What is the Horizontal Gaze Nystagmus Test in Nevada DUI cases?
- 2. When do police administer it?
- 3. How do police administer it?
- 4. How are results measured? What is failing?
- 5. Can I refuse to take it?
- 6. Does passing or not taking the HGN Test mean I will not get arrested for DUI?
- 7. How accurate is it?
- 8. How do I contest the results of the HGN Test?
- 9. Does Nevada law recognize HGN Tests?
- 10. Is it the only field sobriety test ?
1. What is the Horizontal Gaze Nystagmus Test in Nevada DUI cases?
The Horizontal Gaze Nystagmus (HGN) test is a “field sobriety test” that Nevada police administer if they suspect you have been driving under the influence.
It involves the officer holding up a finger or pen – called a “stimulus” – in front of your eyes, and you are instructed to follow the stimulus with your eyes as the officer tracks the stimulus horizontally from side to side.
If your pupils exhibit nystagmus (an involuntary jerking) while following the stimulus, the police may presume you have an illegal blood alcohol content (which is .08% or higher in Nevada).
2. When do police administer it?
The Horizontal Gaze Nystagmus (HGN) test typically occurs within 10-to-30 minutes of when the police officer first makes contact with you. Note that police may be unable to administer the HGN if you are too injured or too intoxicated to take instructions.
Example: After a Nevada Highway Patrol officer pulls someone over for driving erratically, the officer asks for their license and registration and checks if they have any warrants out for their arrest. Meanwhile, the officer is trying to detect the odor of alcohol, whether their eyes are bloodshot and glassy, and if they are speaking in a slurred manner or are otherwise appearing inebriated.
The officer will also ask the driver if they drank. If at that point the officer believes the driver may be under the influence, the officer will demand that they exit the car in order to perform three field sobriety tests (the HGN test, the walk-and-turn test, and the one-legged stand) and preliminary breath test.
If the test results indicate that the driver is intoxicated, the officer will arrest the driver and book them at the police station.
3. How do police administer the HGN Test?
The Nevada police officer stands in front of you and explains that they are going to check your eyes. The officer will also ask you to take off any glasses or remove any hard contact lenses.
At that point, the officer holds a stimulus (usually a pen or finger) 12 to 15 inches straight in front of your eyes and explains that they will be moving the stimulus side to side. Then you will be instructed to keep your head still while following the stimulus with your eyes and not to take your eyes off the stimulus unless instructed.
There are three basic steps to the HGN test:
- Lack of smooth pursuit: The officer tracks the stimulus side-to-side while the officer observes whether your eyes are moving smoothly or jerkily.
- Distinct and sustained nystagmus: The officer tracks the stimulus to a maximum deviation on either side (“maximum deviation” means the farthest your pupils can turn outward). While holding the stimulus at maximum deviation, the officer monitors how distinct and sustained each eye’s nystagmus (involuntary jerking) is.
- Onset of nystagmus prior to 45 degrees: The officer moves the stimulus to either side while checking for nystagmus (jerking) prior to reaching the 45-degree angle mark.
4. How are results measured? What is failing?
Nevada police are watching out for three signs of nystagmus in each eye, totaling six signs of nystagmus in all. Law enforcement calls each of these signs a “clue.”
According to the National Highway Traffic Safety Administration (NHTSA), suspects who display four or more clues (signs of nystagmus) likely have an illegal blood alcohol level of .08 or above.
Therefore, a failing HGN score is when you display four to six clues. A passing HGN score is when you display zero to three clues.
5. Can I refuse to take it?
Yes. In fact, it is advisable for you to refuse to take the HGN test (and other field sobriety tests) because it will leave the prosecution with less evidence to support a guilty verdict for DUI.
However, refusing to take field sobriety tests almost always guarantees that the officer will arrest you anyway. Then once you are arrested, you are legally obligated to submit to a chemical test such as the breath test or blood test.
6. Does passing or not taking the HGN Test mean I will not get arrested for DUI?
Not necessarily. If you score three or fewer clues in the HGN test but fail the other field sobriety tests and the preliminary breath test, the officer will probably elect to arrest you for DUI based on the totality of the circumstances. A failed HGN test is not a prerequisite for a Nevada DUI arrest.
Conversely, failing an HGN test does not guarantee that you will be arrested for DUI. If the officer believes the nystagmus is caused by something other than alcohol or drugs, and if you are not otherwise displaying signs of intoxication, the officer may elect not to arrest you for DUI.
If you never take the HGN test because you refuse to do it or you are too incapacitated, the police may still choose to arrest you for DUI if other evidence suggests you were drinking. You can still be arrested for and convicted of DUI without having taken an HGN test.
7. How accurate is it?
Not very. NHTSA claims that the HGN test is 77% reliable in determining whether you are under the influence of alcohol.1 Therefore, approximately one out of four people who fail the HGN is in fact not intoxicated.
8. How do I contest the results of the HGN Test?
From our experience fighting thousands of Nevada DUI cases, our criminal defense attorneys rely on various methods to contest a failing HGN score. Ten possible reasons for a false HGN score include:
- The officer was improperly trained in administering the HGN or gave you incorrect instructions.
- The officer held the stimulus too close or too far away from your eyes.
- The officers’ eye-level was not above your eye-level.
- The officer’s hand was jerky as they were moving the stimulus from side-to-side.
- The officer incorrectly estimated the 45-degree angle.
- You had taken such medications as seizure drugs, PCP, barbiturates or certain depressants.
- You had a head injury (diagnosed or undiagnosed).
- You were wearing hard contact lenses, which have irritating effects.
- You have an eye disorder marked by twitching, and you were not wearing glasses or contacts to correct it.
- There were flashing lights from the police car or another source in the vicinity (which may cause nystagmus).
Note that none of these factors by itself may cause Nevada DUI charges to get dropped in Nevada. Judges often look to the totality of the circumstances to determine whether you were under the influence. Though the more issues that we can raise to call into question the HGN test’s accuracy, the better for you.
9. Does Nevada law recognize HGN Tests?
Yes, Nevada courts recognize the HGN test as evidence of whether you are under the influence.
In the case State, Dept. of Motor Vehicles and Public Safety v. McLeod, the Nevada Supreme Court held that the arresting officer was correct to administer an HGN test on a driver even though he had a head injury. The Court reasoned that because the driver smelled of alcohol and had bloodshot eyes, the officer had sufficient cause to believe the driver was under the influence and was therefore justified in administering the HGN test.2
10. Is it the only field sobriety test?
No. Nevada police administer a total of three standardized field sobriety tests (FSTs) on suspected drunk drivers. In addition to the HGN, the tests include the
- one-legged stand test and
- walk-and-turn test.
Studies show that the HGN test is more reliable than the other two FSTs.3
Most significantly, note that getting arrested for DUI does not necessarily mean you will ultimately be convicted. Even if you failed the HGN test and/or other field sobriety tests, it still may be possible to show that the prosecutor lacks sufficient evidence to prove guilt beyond a reasonable doubt.
- U.S. Department of Transportation “DWI Detection and Standardized Field Sobriety Testing” NHTSA Student Manual (February 2006): VII/3.
- Dept. of Motor Vehicles and Public Safety v. McLeod (Nev. 1990) 801 P.2d 1390.
- Note 1 at VII/2.