Horizontal Gaze Nystagmus
When looking to determine the level of impairment of a driver who is suspected of driving under the influence, many law enforcement officers will administer a field sobriety test. This is a test that looks to the physical and mental abilities of the defendant to determine how impaired they are from alcohol usage. The problem, however, arises when one considers that this is a test with no objective results. Instead, it is a subjective test with opinionated conclusions. To help in creating standards for these tests, the National Highway Transportation Safety Administration has created guidelines for how these should be administered. One of the most popular includes the Horizontal Gaze Nystagmus (HGN) .
To understand the HGN test, one must understand nystagmus. Scientifically speaking, nystagmus refers to the involuntary jerking of the eye when the inner ear is disturbed. HGN therefore refers to this jerking when it occurs in a horizontal pattern. The reason that the NHTSA uses this as a field sobriety test is that it is believed that alcohol consumption can cause the eye to bounce laterally, with the amount of the jerking to increase with the amount of alcohol in the body's system.
This is typically referred to as Alcohol Gaze Nystagmus and is due to the fact the alcohol can affect the motor control systems of the body. This results in instability and poor motor coordination, which can in turn affect the ability of a person to smoothly control their eye movements. When the nervous system is affected, the eyes can be unable to remain steady and can have an observable effect.
To administer the test, the officer will place the subject in an area with good lighting, although they are not permitted to be facing blinking lights or oncoming traffic as this could disturb the ultimate results of the test. The officer will then use a flashlight to point towards their face. The subject is then asked to follow the tip of a pen with their eyes which is placed from twelve to fifteen inches from their eyes. Should there be a lack of smooth eye movement or distinct jerking, the subject could fail the test.
Although this is a standardized test from the NHTSA, it does not mean that it is without flaws. Should the test be administered by a police officer that is not properly trained or if the officer makes a subjective decision based solely on opinion, you should not be forced to suffer from the results. In fact, in some courts, the HGN test is not admitted as evidence as it can be believed to be insufficient.