The Horizontal Gaze Nystagmus (HGN) test is one of three standardized field sobriety tests that officers give before making a DWI arrest. It is usually the first test given and many people believe they pass the test because they followed the officer’s instructions. This is incorrect. Following the officer’s instructions simply allows the officer to observe your eyes. Although the HGN test seems simple, there are actually many problems with the test that can lead to the false conclusion that a driver was intoxicated.
The officer begins by asking you to stand with your feet together and hands at your sides. He will then tell you to follow his finger with your eyes while he moves it across your face. Officers often use a small pen with a light at the tip, instead of their finger. As the light moves across your face, slightly above eye level, the officer is watching to see if your eyes are able to track the pen smoothly or do they display an uneven jittery motion – called nystagmus.
During the first phase, the officer looks for nystagmus as the eyes move from side to side. This clue is called lack of smooth pursuit. In the second phase, the officer looks to see if the nystagmus is present and continuous for a minimum of four seconds while you look to the extreme left or right. This is called distinct nystagmus at maximum deviation.
In the third phase, the officer looks to see how quickly the nystagmus begins. If he sees your eyes bouncing before his finger moves from your nose to the outer edge of your shoulder, he will count this as a clue. This is called nystagmus onset prior to 45 degrees.
Although this test seems scientific, there are many reasons why the HGN test is not a reliable indicator of intoxication. Nystagmus can be caused by many things other than intoxication. Some medical conditions cause nystagmus. Eye fatigue can cause nystagmus. In fact, taking the HGN test when there is a rapidly changing background in your field of view can also cause lead to a false positive for nystagmus. That means that if you can see flashing police lights or rapidly moving traffic when taking the test, it could have an impact on the result.
The officer may also make an error giving the test. He might fail to make the required number of passes for each eye. Or, he can wrongly estimate the 45% angle that is required for the third phase of the test. He or she might even think he sees nystagmus, when it really isn’t there. Officers are warned that can happen in their training materials. “If you think you see only slight nystagmus at this state of the test, or if you have to convince yourself that nystagmus is present, then it isn’t really there.” 2013 NHTSA Manual on DWI Detection and Field Sobriety Testing, Chapter on HGN p. 32. That warning is given because it is a real mistake that can be made.
What is worse, in almost every case, the video will not show your eyes as you are taking the test. That means your lawyer can only check to see if the officer gave the test correctly. We have no way to verify what the officer saw. At times the HGN test results will even contradict the results from the other standardized field sobriety tests. In fact, I have seen cases where people pass the two balance tests, but fail the HGN test and are arrested for DWI. This really shouldn’t happen. The HGN test does not demonstrate the reliability that should be required of a test used to convict someone with a crime.
It is important that every case is reviewed by a DWI lawyer who understands the HGN test and its limitations. That review should include reviewing the arrest report as well as any video evidence. In addition, the ALR hearing often allows a DWI lawyer to test the officer’s knowledge of the HGN test. If you are facing a DWI arrest it is critical that you have this kind of review.