Horizontal Gaze Nystagmus (HGN)
As was previously discussed, Horizontal Gaze Nystagmus (HGN) is the involuntary jerking of the eyes as they look to the side. There are 10 steps for an officer to correctly administer the test. If the test is not administered to the National Highway Traffic Safety Administration (NHTSA) guidelines, the validity of the test may be compromised. This means the ability of the test to consistently produce accurate and reliable results. In this article, the most important administrative procedures will be discussed.
An officer is required to position a stimulus (pen, pen light, finger tip etc.) approximately 12-15 inches in front of the person’s face and slightly above eye level. Research has shown that a stimulus held too high, produced false positives at a rate of 91%. A false positive for HGN is a person having a blood alcohol concentration (BAC) of less than 0.08 grams but displaying (4) or more clues.
An officer is next required to medically qualify the person for the HGN test. The first step is checking for Resting Nystagmus, which is the involuntary jerking of the eyes as they are looking straight ahead. The officer needs to ensure that this is not present. The next step is to check for equal pupil size. The officer needs to confirm that the person’s pupils are equal in size. The last step is checking for equal tracking. To properly check for equal tracking, an officer must move the stimulus at a rate that takes approximately (2) seconds from the center of the person’s face to the point that the eye can move no further (maximum deviation) to the person’s left. The officer then moves the stimulus all the way to maximum deviation on the person’s right at a rate that takes approximately (4) seconds. The officer then moves the stimulus back to the center at a rate of approximately (2) seconds. It is very important that an officer properly medically qualifies a person for HGN before checking for clues. If not, it is possible for the person to have other issues that could affect the results of the test.
After the person is medically qualified, the officer then checks for the first clue, Lack of Smooth Pursuit. To properly check for Lack of Smooth Pursuit, an officer must move the stimulus at a rate that takes approximately (2) seconds from the center of the person’s face to the point that the eye can move no further (maximum deviation) to the person’s left. The officer then moves the stimulus all the way to maximum deviation on the person’s right at a rate that takes approximately (4) seconds. The officer then moves the stimulus back to the center at a rate of approximately (2) seconds. This is to be completed (2) times. The officer is looking for the eye to jerk as it is moving side to side. It is compared to the movement of a windshield wiper on dry glass.
The basis behind these time parameters is that a normal sober person’s eye can smoothly follow an object at approximately (30) degrees per second. The field of view from center to maximum deviation is approximately (60) degrees. By moving the stimulus at a rate of approximately (2) seconds out, the stimulus is being moved at approximately (30) degrees per second. Why is this so important, because if an officer moves the stimulus faster than that rate, it is possible that the person’s eyes will not be able to smoothly follow the stimulus. This can induce the same jerking that an officer is looking for, and means the Nystagmus could be caused by the officer.
The next clue that an officer checks for is Distinct and Sustained Nystagmus at Maximum Deviation. The officer moves the stimulus all the way to maximum deviation of the person’s left. The officer then must hold the stimulus at maximum deviation for a minimum of (4) seconds. The officer then moves the stimulus all the way to maximum deviation of the person’s right. The officer again must hold the stimulus at maximum deviation for a minimum of (4) seconds. This must be done (2) times for each eye. The officer is looking for a distinct (clearly visible) and sustained (continuous) jerking of the eye while at maximum deviation.
The importance behind holding for a minimum of (4) seconds is to ensure that Distinct and Sustained Nystagmus at Maximum Deviation is observed. There is a Nystagmus that can occur in otherwise normal sober people called Endpoint Nystagmus. This naturally occurring Nystagmus can be present when the officer initially gets to maximum deviation. It normally will go away within a second or two. By holding for (4) seconds the officer is able to confirm that the observed Nystagmus is consistent with the clue and reduce the likelihood of it being the naturally occurring Endpoint Nystagmus.
The last clue that an officer checks for is Onset of Nystagmus prior to 45 degrees. The officer moves the stimulus slowly at a rate that takes approximately (4) seconds to get to 45 degrees to the person’s left. The officer is looking to see the point at which the eye starts jerking. The officer will then stop the stimulus and hold it steady at that point. The officer then ensures that the jerking is still present and is prior to a 45 degree angle. If the jerking is not still present then the officer continues moving the stimulus until they observe jerking or get to a 45 degree angle. If nystagmus is not observed prior to approximately 45 degrees, they are to stop and hold the stimulus at an approximate 45-degree angle to verify the nystagmus is not present. The officer will then check the person’s right eye, and then do another pass for both eyes
There are (2) common errors that officers make when checking for Onset of Nystagmus prior to 45 degrees. The first is that the officer does not stop and hold the stimulus steady to confirm that the jerking is present. This is necessary for the officer to ensure that the Nystagmus is actually present. The second is that the officer moves the stimulus to or past 45 degrees. It is only a clue if it occurs prior to 45 degrees.
In summary, HGN is a “scientifically validated” test that officers will testify to being extremely accurate. Remember, that the validity of the test may be compromised if the officer does not follow the NHTSA guidelines for the administration of this test. It is very common for officers to not administer HGN correctly. A DUI/SFST expert can review your case and determine if the officer followed these guidelines.
About the author: Joshua Ott operates Caselock Inc., specializing in expert testimony and reviews for cases involving alcohol and/or drug impairment. Joshua has extensive knowledge and training obtained from ten years as a police officer in Metro Atlanta. He has extensive experience training law training law enforcement officers as well as courtroom preparation and testimony. He resides in Woodstock, Georgia with his wife, daughter and Miniature Schnauzer, Gus. For more information, visit caselockinc.com.