Alcohol Gaze Nystagmus (AGN) is a physical phenomenon that occurs when the body consumes alcohol. AGN can be seen as the eyes slowly drifting before suddenly snapping back to their previous position, also known as jerk nystagmus. This can look like blurry vision to the individual experiencing AGN.
AGN occurs because of the effects of alcohol on the central nervous system. As alcohol is processed throughout the body, it can depress the function of the brain. This depression in function can cause the eyes to begin to function incorrectly, allowing temporary periods of drift before being suddenly corrected. This can also result in a loss of balance.
AGN is also a common phenomenon that law enforcement officers will look for when stopping someone under suspicion of driving under the influence (DUI). Officers may test for AGN by administering either a horizontal or vertical gaze nystagmus test. This test will be administered by asking the subject to observe an object such as a pen as the officer moves it from side to side or up and down. The purpose of this test is to scan the subject for any lag in following the object or for any sudden, jerky eye movements which may be caused by AGN.
Officers could also try to screen for Positional Alcohol Nystagmus (PAN). This is more difficult to test for since it requires the subject to lay down and is difficult to observe.
When checking for AGN, officers may administer a test for several manifestations of AGN. These manifestations include:
While it is possible for a nystagmus to be caused by alcohol consumption, there are also many other possibilities. As recently as July 2021, doctors have called into question the effectiveness of AGN tests at roadside stops. A number of medical conditions can obscure AGN including:
These conditions can all make it impossible to determine whether or not the individual being pulled over is actually intoxicated or merely exhibiting symptoms of a lifelong, neurological nystagmus condition.
In addition to diagnosed medical conditions, research also shows that people with otherwise normal vision can develop Gaze-evoked nystagmus (GEN) when required to stare at an object in a direction other than directly forward. This variant of GEN, called "End point nystagmus" or physiological nystagmus, is considered entirely normal when staring at an object at an angle of less than 30 degrees. Despite this, an officer administering an AGN test may hold the object at an incorrect angle, observe a naturally occurring nystagmus, mistake a pendular nystagmus for a jerking motion, and erroneously claim that the individual is intoxicated.
For this reason, doctors believe that having a medically inexperienced officer administer a test that medical professionals struggle to consistently administer correctly in roadside conditions is unhelpful and frequently incorrect. Even a mistake as simple as seeing a pendular nystagmus, in which the eye moves slowly rather than jerkily, can result in a false positive.
Similarly, officers who are not medically trained may mistake normal positional nystagmus for PAN. There can also be instances of optokinetic nystagmus, where the eye watches sharply contrasting images such as an object that is reflecting the alternating light of police sirens. Before administering a test for AGN, the officer should also ensure that there is no resting nystagmus, which may bias the results of the test.
Since police officers are not trained medical professionals, they are working under less than ideal conditions, and they are seeking to justify their conclusion that they made a correct arrest, many medical professionals have testified that the AGN test is not accurate or replicable enough to be used as solid evidence for a DUI conviction.
AGN is a complex medical phenomenon that can easily be mistaken under the conditions present at the side of a road at night. If you find yourself facing a DUI charge on the merits of an AGN test, you should consult with an experienced DUI attorney. A DUI attorney can improve the outcome of your case by using experience and testimony to soften the case against you. They could cross examine the officer who administered the test to expose the flaws in their methodology. A DUI attorney could also produce a nystagmus doctor to testify to the flaws inherent in the AGN test and the various ways that obscuring conditions such as the angle of the object or normal gaze-evoked nystagmus could have wrongfully been used to determine that you were intoxicated at the time of the test.