The horizontal gaze nystagmus (HGN) is a sobriety test that police officers use to check for possible impairment. A nystagmus is an involuntary jerking or twitch in the eyes, and it occurs when you look to the side over 45 degrees, which triggers your peripheral vision. When you’re under the influence of alcohol, this jerking of the eyes can occur before 45 degrees, giving police an indicator of alcohol use.
The test itself is simple enough. The officer will stand in front of you and hold a penlight in front of your eyes approximately a foot from your face, instructing you to watch the light. They will then move the light from side to side, looking for a few things that can occur in one or both eyes. The first is eyes that move with twitches instead of moving smoothly. The second is if your eyes start twitching when you’ve moved them all the way to the side, and the third is if your eyes start twitching before they’ve reached a 45-degree angle.
For the HGN test to be admissible in court, the officer must be able to see your eyes clearly, so they must conduct the test in an area with sufficient lighting or use a flashlight on your face. They also must make sure you’re not looking towards flashing lights or oncoming headlights, as these can cause nystagmus even in people who aren’t impaired.
One thing that many drivers don’t realize is that they’re not required by law to take the HGN or any other field sobriety test. A police officer can request that you take a field sobriety test, but they can’t force you to take it, and you should always exercise your right to refuse these type of tests. The reason for this is because when an officer has you take a field sobriety test, they’re only collecting evidence that they can use against you. They’re asking you to take the test because they already suspect that you’re impaired, which means they’re planning to arrest you.
Drivers take field sobriety tests because they think that they need to and that if they pass, the officer will let them go. Neither of these are true.
Police officers often make it seem like you need to take a field sobriety test or that it’s in your best interest to do so. They may use wording that tricks you into giving up your legal rights, such as saying “I’m going to have you take a quick sobriety test,” which sounds like you don’t have a choice in the matter. You do, and the smart response is “I don’t consent to any tests.”
Will the officer let you go if you do well enough on your field sobriety test? The chances of that happening are minute. This is the process of gathering evidence for them, not determining your guilt or innocence. Also keep in mind that all field sobriety tests have a subjective element to them. The officer is making the determination on whether or not you demonstrate impairment, and if they already suspect that you’re impaired, how impartial are they going to be?
An officer who has pulled you over can request that you take a field sobriety test, which requires your consent. They can also ask you to take a breathalyzer or arrest you, both of which require probable cause. Your performance on that field sobriety test can give them the probable cause they need to have you take a breathalyzer or arrest you, which is why they’ll typically do the field sobriety test first.
For the officer, it’s a simple three-step process: get probable cause through field sobriety tests, use that probable cause to have you take a breathalyzer and then arrest you if you were driving under the influence. Refusing to perform any field sobriety tests allows your defense attorney to argue that the officer didn’t have probable cause in arresting you. This doesn’t necessarily mean that the judge or jury will agree, but you’re at least minimizing the evidence that can be used against you.