By: DUI Lawyer Cory Yager, Ex-cop with over 1000 DUI arrests, FTO (field training officer) and HGN Certification (participant and instructor)
The HGN Meaning. The DUI eye test for alcohol use used by police in a driving under the influence investigation is officially known as the horizontal gaze nystagmus (HGN) test, or HGN eye test. It is one of three standardized field sobriety tests (SFSTs) that were “approved” for use by police in gathering roadside “evidence” to justify probable cause for arrest.
In every level of NHTSA training, the HGN evaluation is touted as being the MOST scientific of the 3-test DWI battery. It is different in that it is a psycho-physical test, and the walk and turn (WAT) and one-leg stand (OLS) evaluations are divided attention tasks.
What is nystagmus meaning? Simply put when a person’s eyes show side-to-side, involuntary jerking of the eyes created HGN clues, THAT observed movement in the eyes is what nystagmus is.
Before NHTSA “sanctioned” police using the HGN field test, no one in history claimed that these three roadside tests could reliably predict a person’s blood-alcohol level.
If this was possible, then officers could reliably tell which persons were “over the legal limit” and which ones were not. It is important to note that NEVER have the field sobriety evaluations been able to predict driving IMPAIRMENT.
How and Why Field Sobriety tests were Invented
The horizontal nystagmus alcohol test is an evaluation “dreamed up by,” designed, promulgated, and funded by a brand-new Ph.D. candidate in southern California named Dr. Marcelline Burns. Around 1970, she wrote her psychology Ph.D. thesis on the need for police to have some roadside, standardized exercises or tests, to bolster the law enforcement officers’ (LEO) DUI arrest decisions.
The National Highway Traffic Safety Administration (NHTSA) was launched in 1970. Dr. Burns submitted her thesis to NHTSA to see if they would “buy in” to this idea. They did, and she ultimately received every federal funding contract for multiple “studies” to support the scientific basis for using such tests.
Prosecutors welcomed “something new and more scientific.” In 1999, The American Prosecutors Research Institute published a detailed guidebook on the horizontal gaze nystagmus test clues to be used to prosecute intoxicated driving cases. This included several lists of questions to ask different types of defense experts. This was called The Horizontal Gaze Nystagmus: The Science and the Law.
The problem with the Prosecutor’s guide is that no independent research or analysis of the underlying “science” was attempted since the prosecutors assumed that no criminal defense attorneys would successfully challenge field test evidence. The report cites favorable, pro-prosecution case law from all states as a crib sheet for their fellow prosecutors.
Since that publication about the nystagmus test procedure was released, dozens of court opinions have either disavowed unsubstantiated police claims, or overturned convictions when a Judge failed to do his or her job as the gatekeeper of proper forensic evidence at trial. Almost all appellate losses for the state had to do with faulty administration of the HGN evaluation.
This HGN DUI test is 100% voluntary and should NEVER be agreed to or “attempted” by any detained driver. The overarching reason to not take the police gaze test, nystagmus can be induced by improper administration.
After all, no formal medical training is given to officers. Plus, (in most states) the person administering the test, which is a medical test, only must have his or her high school GED. Thus, you can be arrested off a botched effort to properly assess your eye movements and have this poor-quality “evidence” used to convict you.
Even Dr. Burns concedes that the NHTSA three-test battery CANNOT predict alcohol impairment. Based on the medical college information cited below, the most common source of this error, is holding the stimulus too high, which CAUSES nystagmus.
“The movement of the eyeballs are controlled by three pairs of extrinsic muscles. The superior and inferior recti muscles control vertical movements, and the lateral and medial recti muscles move the eyeball laterally. The superior oblique muscle moves the eyeball inferiorly and laterally and the inferior oblique muscle moves the eyeball superiorly and laterally.”
What is the Eye Nystagmus Test used by Police During a DUI Investigation?
It is a roadside screening test that is OFFERED to drinking drivers by a law enforcement officer who suspects impaired driving. This is used by police for the officer to claim that he or she saw “X” number of clues (cues was the original NHTSA word for “errors”) in the DUI suspect’s eyes during the nystagmus alcohol test.
The “cues” will be observed as the stimulus is passed in a lateral (horizontal) fashion, across the detainee’s field of vision. The subject’s head should not be tilted backward, and his or her chin should be at a 90-degree angle to the ground.
Police officers in Georgia use this field sobriety test at the roadside as a means of bolstering their probable cause to arrest suspected drunk drivers. Of critical importance is for the stimulus to be either at eye level, or slightly above exact eye level, to prevent other eye muscles (superior or inferior rectus or oblique muscles) from pulling up or down.
The most common error, in the administration of the movements, is holding the “target” too high. Anything above eyebrow level is too high. That warning is critical since this exam will be compromised for accuracy if anything except the side-eye muscles (medial rectus and lateral rectus) are smoothly pulling back and forth.
The speed of the movement of that pen, fingertip or penlight is critically important to proper administration. When moved too fast, the excessively fast passes will trigger nystagmus, even when the subject has zero alcohol. In addition, holding the stimulus too close or too far away compromises reliability since the validation studies used 12″ to 15″ from the face as the proper distance for the stimulus to be positioned.
In the video below, a Georgia State Patrol officer demonstrates how to properly instruct a driver how to perform the DUI eye test and the signs law enforcement officers analyze during the HGN.
The SFST Instructions for the Horizontal Nystagmus Test
Many steps are needed after full and complete screening of the proposed test subject starts the HGN “passes.” One step is the resting nystagmus DUI beginning point. The officer’s purpose is to check for “resting” nystagmus, but if he or she sees natural nystagmus, the manual does not advise to discontinue the eye test.
Then, check for equal tracking, by making two passes (with the HGN pen or finger) for each eye, to assure that each eye can track properly. That requirement of 2 passes for all movements of the stimulus applies to ALL the HGN progressive steps.
Understanding the horizontal gaze nystagmus clues. The first scored test is lack of smooth pursuit, followed by checking for distinct and sustained nystagmus at maximum deviation. The distinct nystagmus at maximum deviation must be continuous for 4 seconds or longer, at each endpoint.
Finally, the third set of passes is to look for the onset of nystagmus prior to 45 degrees. This is the pass that 90% of officers botch, even when they substantially comply with the first two sets of passes.
In the past decade or so, the IACP added a step of conducting an unscored vertical gaze nystagmus (VGN test) movement, meaning to take the stimulus up and down, twice. No such VGN requirement was included (or studied) in the multiple research studies conducted by Dr. Burns and her team.
So, what does vertical nystagmus indicate? This final set of passes, if VGN is present, is supposed to mean EITHER a high dose of alcohol for this test subject OR that PCP or dissociative anesthetics are present in the person’s system.
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