The Horizontal Gaze Nystagmus (HGN) Test is a non-invasive eye exam that police administer on suspected drunk drivers in Nevada. Depending on the results of the HGN, preliminary breath test, and other field sobriety tests, the officer may arrest the driver for violating Nevada DUI Law.
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.)
- What is the Horizontal Gaze Nystagmus Test in Nevada DUI cases?
- When do police administer it?
- How do police administer it?
- How are results measured? What is failing?
- Can I refuse to take it?
- Does passing or not taking the HGN Test mean I will not get arrested for DUI?
- How accurate is it?
- How do DUI defendants contest the results of the HGN Test?
- Does Nevada law recognize HGN Tests?
- 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 on suspected drunk drivers. It involves the officer holding up a finger or pen…called a “stimulus”…in front of the suspect’s eyes, and the suspect is instructed to follow the stimulus with his/her eyes as the officer tracks the stimulus horizontally from side to side. If the suspect’s pupils exhibit nystagmus (an involuntary jerking) while following the stimulus, the police may presume the suspect has 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 the suspected drunk driver.
Example: A Nevada Highway Patrol cop is driving down the I-15 and notices someone allegedly driving a car erratically. Then the cop pulls over the driver and asks for his/her license and registration and checks if the driver has any warrants out for his arrest. Meanwhile, the cop is trying to detect the odor of alcohol, whether the drivers’ eyes are bloodshot and glassy, and if the driver is speaking in a slurred manner or is otherwise appearing inebriated. The cop will also ask the driver if he/she drank. If at that point the cop believes the driver may be under the influence, the cop will demand that the driver 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 cop will arrest the driver and book him at the police station.
Note that sometimes police are unable to administer the HGN if the suspect is injured or too intoxicated to take instructions.
3) How do police administer it?
The Nevada police officer stands in front of the suspect with his/her weapons away from the suspect and explains that he/she is going to check the suspect’s eyes. The officer will also ask the suspect 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 the suspect’s eyes. The officer explains that he/she will be moving the stimulus side to side and instructs the suspect to keep his/her head still while following the stimulus with his/her eyes and not to take his/her eyes off the stimulus unless instructed. There are three basic steps:
- Lack of smooth pursuit: The officer tracks the stimulus side-to-side while the officer observes whether the suspect’s 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 the suspect’s 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.
In short, the officer checks for three distinct things in either eye: lack of smooth pursuit, distinct and sustained nystagmus, and the onset of nystagmus prior to 45 degrees.
4) How are results measured? What is failing?
As explained in the previous question, Nevada police are watching out for three (3) signs of nystagmus in each eye, totaling six (6) 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 the suspect displays four to six clues. A passing HGN score is when the suspect displays 0 to 3 clues.
5) Can I refuse to take it?
Yes. In fact, it is advisable for a DUI suspect 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. However, refusing to take field sobriety tests almost always guarantees that the officer will arrest the suspect anyway. And once the suspect is arrested, he/she is 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 the suspect scores 3 or fewer clues in the HGN Test but fails the other field sobriety tests and the preliminary breath test, the officer will probably elect to arrest the suspect 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 does not guarantee that the suspect will be arrested for DUI. If the officer believes the nystagmus is caused by something other than alcohol or drugs, and if the suspect is not otherwise displaying signs of intoxication, the officer may elect not to arrest him/her for DUI.
There are some cases where a suspected drunk driver never takes the HGN test because he/she refuses to do it or he/she is too incapacitated. But even in these circumstances, the police may choose to arrest the suspect for DUI if other evidence suggests he/she was drinking. A person 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 a driver is 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 DUI defendants contest the results of the HGN Test?
There are several ways that a DUI defense attorney can contest a failing HGN score. Possible reasons for a false HGN score include:
- The officer was improperly trained in administering the HGN
- The officer held the stimulus too close or too far away from the driver’s eyes
- The officers’ eye-level was not above the driver’s eye-level
- The officer’s hand was jerky as he/she was moving the stimulus from side-to-side
- The officer gave the driver incorrect instructions
- The officer incorrectly estimated the 45-degree angle
- The suspect had taken such medications as seizure drugs, PCP, barbiturates and certain depressants
- The suspect had a head injury (diagnosed or undiagnosed)
- The suspect was wearing hard contact lenses, which have irritating effects
- The suspect has an eye disorder marked by twitching, and he/she was not wearing glasses or contacts to correct it
- There were flashing lights from the cop 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 a suspect was under the influence. But the more issues that defense attorneys can raise to call into question the HGN Test’s accuracy, the better for the defendant.
9) Does Nevada law recognize HGN Tests?
Yes, Nevada courts recognize the HGN as evidence of whether a driver is 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 (3) standardized field sobriety tests (FSTs) on suspected drunk drivers. In addition to the HGN, the tests include the one-legged stand test and the 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 the driver will ultimately be convicted. Even if the suspect 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.
Arrested for DUI in Nevada? Call an attorney…
Are you facing charges for “drunk driving” in Nevada? Call our Las Vegas criminal defense attorneys for a consultation. We may be able to work with the prosecutor to reduce or dismiss your charges. And if necessary, we are prepared to take your case to trial and fight for a non-guilty verdict.
In California? Read our article on California HGN laws.
1 U.S. Department of Transportation “DWI Detection and Standardized Field Sobriety Testing” NHTSA Student Manual (February 2006): VII/3.
2Dept. of Motor Vehicles and Public Safety v. McLeod, 801 P.2d 1390, 106 Nev. 852 (1990). See also United States v. Hernandez-Gomez, No. 2:07-0277RLHGWR, 2008 WL 1837255, at *7 (D. Nev. Apr. 22, 2008).
3Id., at VII/2.