Call For A Free Consultation: (770) 387-4529

Field Sobriety Tests: Part 1

HGN/The Eye Test

The eye test is one of the 3 NHTSA (National Highway Traffic Safety Administration) approved tests for determining whether a driver is drunk. HGN stands for Horizontal Gaze Nystagmus.

 So what is it?

NHTSA claims that the HGN test is the most accurate in testing alcohol impairment of a driver. When performing HGN, the officer will do a series of tests to look for nystagmus, which is an involuntary jerking of the eyes. According to NHTSA, the higher blood alcohol level the more noticeable the condition becomes.

When the officer asks you to complete the HGN test, he or she does not need to ask you in any formal way or tell you that this is a field sobriety test. I recently had a client who was simply asked if the officer could take a look at his eyes. He agreed, not realizing he was being asked to perform a field sobriety test.

It is very important to note a couple of things here. First, you do not have to take any field sobriety tests. Second, the police can lie, trick, and manipulate you in to performing field sobriety tests.

If you agree to take the test, it begins with the officer giving test instructions. The officer will ask you to look at his finger or some other object he is holding, such as a pen, and to follow it with your eyes while keeping your head still. Pay close attention to the instructions and follow them as they are given. Failure to comply with the instructions may be used against you as evidence of impairment.

The officer will begin by moving the object side to side in front of your eyes. If it is dark, the officer will also shine a flashlight in your face. The movements that the officer makes with his finger or pen are called passes. The officer will be looking for a total of six clues that indicate alcohol impairment. Below is how the “clues” break down for each pass.

  • Pass one and two: Lack of smooth pursuit in the left eye and right eye.
  • Pass three and four:  distinct and sustained jerking at what is called “maximum deviation.” This refers to the extreme corners of each the left and right eye.
  • Pass five and six:  onset of jerking prior to 45 degrees.

NHTSA says that if four or more clues are present there is a 77% chance that the driver has a Blood Alcohol Content (BAC) of .10 or higher.


From a legal standpoint, there are several problems with the HGN test.

First, the American Optometric Association indicates that there are a multitude of conditions (some that are very common) that may cause nystagmus, even if the person is sober. These include:

  • Nearsightedness or Astigmatism
  • Inflammation of the inner ear such as Labyrinthitis or Meniere’s disease
  •  Certain prescription medications
  • Head injury or concussion
  • Thiamine or vitamin B12 deficiency
  • Stroke
  • Diabetic Neuropathy
  • Additionally, strobe lights (like the ones from the patrol car) or passing traffic may cause eye jerking.

Second, a 77% chance that a person has a .10 BAC is not at all very certain. If your, child came home with a 77 on a test, he or she got a D. There is a 23% chance that even when the test is given perfectly that it will return a false positive.

Third, the police officer who suspects that you are impaired is the only person deciding if your performance indicates whether any of the clues were present. The test is also reliant on the officer to conduct the test as outlined by NHTSA. Oftentimes, the tests are not conducted correctly and that can skew the results.

You need an attorney who is knowledgeable about HGN and other field sobriety tests to review your case to determine what defenses you may have.

If you have been arrested and charged with DUI contact Block Law today at (770) 387-4529.