Aside from blood alcohol tests, the most important evidence of impairment that police, prosecutors, judges, and juries rely on in driving while intoxicated cases are the results of the field sobriety tests. Most of these tests are difficult for most anyone to pass, whether sober or impaired. The key to successful defense against possible false accusations by police or prosecutors is to know and understand the tests before you decide to comply with the officer’s request and take them.
Of the three standardized field sobriety tests (SFST’s) that are routinely conducted in DWI cases, the one that is the least understood by the general public, judges, and prosecutors alike is the Horizontal Gaze Nystagmus Test (HGN). It is the most scientific test of the three most common SFST’s, and it can actually be the most reliable. However, if it is conducted improperly, the results can be severely compromised. Although the results can be very reliable to determine whether there is alcohol in the blood stream, the test is only as good as the person administering it.
Many people believe that when an officer is conducting the test of the eyes they are simply checking to see whether the subject’s head is moving or whether the subject can follow simple instructions. In reality, the officer is checking for “nystagmus” which is an involuntary jerking of the eye. There are several types of nystagmus, but only alcohol and a few other drugs actually cause horizontal gaze nystagmus. When under cross-examination by a skilled defense attorney, most officers will not know the difference between HGN and other forms of nystagmus such as fatigue nystagmus, optokinetic nystagmus, or nystagmus caused by a previous head injury. Of course, if the trained police officer doesn’t know the difference, neither will the judge or jury. That is why it is important for the officers to be cross-examined on these details in order to impeach their credibility. If they don’t know whether what they are seeing is caused by alcohol or whether is it caused by something else, how can a judge or jury be convinced beyond a reasonable doubt?
During the test, the officer is looking for six potential clues of impairment. In each eye the officer is looking: 1) to see whether the eye moves smoothly from side to side or does it jerk noticeably (this portion of the test is known as lack of smooth pursuit); 2) whether the eye jerks distinctly when it moves as far to the side as possible and is kept there for a minimum of four seconds (this part of the test is known as distinct and sustained nystagmus at maximum deviation); and 3) whether the subject’s eye starts to jerk noticeably as it moves toward the side prior to it reaching a 45 degree angle (this is known as onset of nystagmus prior to 45 degrees). If all six of these clues are present, studies show that the test has a 77% accuracy rate at detecting subjects at or above a 0.10 BAC.
Although potentially 77% accurate, the test must be conducted precisely according to protocol. If not, the results are substantially compromised. When conducting a roadside field sobriety test, the officer’s patrol car is usually equipped with a dashcam that is recording the entire incident on both video and audio. Unfortunately for those who have been pulled over it is up to the individual officer to save the video as evidence. It is not unheard of to see an officer fail to do so because the video is often the only way that their performance in conducting the HGN can be impeached. Do not be afraid to ask the officer to save the dashcam video of the arrest. There is still nothing that requires the officer to do so, but it is worth asking because the evidence can be critically important.
In conducting the HGN, the following protocol must be followed:
The stimulus (finger, tip of pin, etc.) must be held approximately 12-15 inches from the tip of the subject’s nose.
The officer must check to make sure that the eyes track equally, that the pupils are of equal size, and that there is no resting nystagmus. The presence of any of these things could mean there was a previous head injury by the subject or resting nystagmus could detect the presence of a disassociative drug such as PCP, which can be dangerous for the officer.
First Clue – Check for Smooth Pursuit – Check suspect’s left eye first. Begin from center of the nose to the maximum deviation in approximately 2 seconds. Then check the right eye by moving back across the subjects face to a maximum deviation at approximately a 4 second pace. Then go back to center approximately 2 seconds. You then must repeat the process always doing the test twice for each eye.
Second Clue – Check for Distinct and Sustained Nystagmus at Maximum Deviation – Check the left eye first. Eye must follow stimulus to maximum deviation (no white showing in corner of eye). Eye must be held in this position for at least 4 seconds in order for this clue to be scored. Check the right eye. Again, repeat in each eye.
Third Clue – Check for Angle of Onset Prior to 45 Degrees – Check the left eye first once again. The eye must follow the stimulus from the center of the suspect’s nose to near the edge of the suspect’s shoulder to a 45 degree angle, leaving some white showing in the corner of the eye, at approximately a 4 second pace. Check the right eye, and repeat the entire cycle again in each eye.
The final steps of the test includes checking for vertical gaze nystagmus, which is the same process as checking for smooth pursuit only up and down, and the last thing to do is to check for lack of convergence. Both VGN and lack of convergence are not clues to be scored during the HGN test, but could aid the officer in developing suspicion of either a high level of alcohol in the blood or other types of drugs as possible intoxicants. If each of the above steps are conducted appropriately, the test should take no less than 64 seconds and realistically probably longer for a good, accurate test.
Once again, if this test is conducted properly by the arresting officer it can be very solid evidence of the presence of alcohol in a person’s system. However, to uncover poor administration of the HGN, and any other FST, it takes a skilled criminal defense attorney who is knowledgeable in the area of DWI defense.
