One of the standardized field sobriety tests that today’s officers employ is the Horizontal Gaze Nystagmus test (HGN) also called the “eye test.”
The HGN is one of the most tricky and generally most damaging pieces of evidence a prosecutor can present in a borderline OWI trial. It is also a very powerful tool used by the police to gain “reasonable suspicion” to bring a suspect down to the station for the final breath test.
The biggest problem with the HGN is that it is based totally on the officer’s subjective observations, and that it is completely unverifiable by neutral means. By the nature of the test itself, the eye movements cannot be recorded by a video camera, and thus the officer’s word is the only verification that is needed to secure a breath test and ultimately, a conviction.
The HGN consists of three separate stages. All of these stages are performed as the officer asks the suspect to follow his finger (or a small “stimulus” such as a pen) with his eyes from side to side, without moving his head.
The first thing the officer is looking for is “lack of smooth pursuit.” There is scientific evidence that an intoxicated person will develop a nystagmus (meaning a ‘bounce’ or ‘skip’) of the eyes, from side to side, while that person is intoxicated. The problem with this test is that there are various other sources that can cause a nystagmus, including nicotine and aspirin. The science says that all eyes offer some sort of horizontal nystagmus, but with intoxication by alcohol, this nystagmus is more distinct.
The officer will also look for “nystagmus prior to 45 degrees.” The science states that eyes will also offer a nystagmus (again, a “bouncing”) at around a 45 degree deviation. When a person is intoxicated, this nystagmus can occur prior to a 45 degree angle. This angle is measured as the lateral degrees from a straight-forward view. As a rule of thumb, for every degree prior to 45 degrees that the officer observes a nystagmus, that indicates (X*0.01) + 0.05 BAC where X = degrees prior to 45. The problem with this is that officers do not use any sort of tool to estimate the 45 degree angle. Again, the State alleges that these officers are trained to detect the 45 degree angle accurately, but an error of only 5 degrees is the difference between a 0.05 and a 0.10 BAC! It is truly a ridiculous proposition that an officer could accurately determine were the 45 degree angle begins.
Finally, the officer is looking for a “distinct nystagmus at maximum deviation.” This would be a very large bounce when the suspect is looking to the side as far as he possibly can.
The HGN is dangerous because it requires careful administration to be accurate, and those conditions simply do not exist in the field.