Criminal Law

HGN Test: What You Need to Know

Many people are somewhat familiar with some of the tests that are given by police officers when they are investigating a possible DWI. The first test which comes to mind for people when they think about DWI testing is the eye test, or the Horizontal Gaze Nystagmus test. To understand the HGN test, you will first need to know what Nystagmus is. Nystagmus is defined by the American Optometric Association as “a vision condition in which the eyes make repetitive, uncontrolled movements.” Basically, Nystagmus is when your eyes look like they are jerking when they are following an object; this is something that is involuntary and cannot be controlled.

Due in part to a person’s inability to control Nystagmus, it is said to be the most reliable of the field sobriety tests. A total of six clues can be found during the administration of the HGN testing (3 clues for each eye). The test is designed to start with the person’s left eye being examined for any of the three cues. Afterwards, the the right aeye is examined.

The first clue officers will look for is lack of smooth pursuit. They are looking to see if your eyes track smoothly from one side to the other, or whether your eyes begin to start jerking, which would be an indication of nystagmus. When you are impaired by alcohol, your eyes lose their ability to track objects smoothly. The officer will check each eye individually for lack of smooth pursuit.

Second, the officer will check to see how each eye reacts once it has moved as far to one side as possible. Officers are trained to look for “distinct and sustained” nystagmus at what is referred to as at “maximum deviation.” What the officer is looking for in each eye at this part of the test is if your eyes are twitching or jerking when you are looking as far to one side as possible. The officer will observe each eye individually and may observe one clue for each eye during this part of the test.

The third thing an officer will be looking for is referred to as “onset of nystagmus prior to 45 degrees.” When the officer is watching the eyes move from one side to the other, they are looking to see if your eyes start jerking before the imaginary 45-degree point during the test. Again, an officer must observe each eye individually and may observe one clue for each eye during this portion of the test.

NHTSA bases the use of the HGN test off a study by the Southern California Research Institute. Through the research provided by SCRI, the HGN test is said to be 77% accurate at detecting impairment in a person who has a blood alcohol level of .01 or higher.

Of all field sobriety test administered, NHTSA purports the HGN to be the most reliable of the field sobriety tests. However, the HGN test is rarely used alone. In most potential DWI encounters, police will use a battery of tests to complete their assessment of whether or not an individual is impaired. Some of the most popular tests used in conjunction with the HGN are the walk and turn and the one leg stand test. Both of which we will break down in future blogs.

DWI cases are very technical and many precise steps must be followed by an officer to get a correct assessment. Fortunately, at wh Law | We Help, we understand the procedures which must be followed and are able to pick out the issues when protocols are not performed correctly. If you or someone you know has been charged with a DWI in Arkansas, contact our offices and speak to an experienced Arkansas DWI attorney today.

About the Author
Degen Clow Arkansas Lawyer

Degen D. Clow

Partner

Degen Clow joined wh Law in 2015 after serving as a Deputy Prosecuting Attorney for several years in Pulaski County. During that time, he spent almost every day in court, which he now considers his office away from the office. He developed confidence and, most importantly, learned what it takes to beat a criminal charge. Before law school, Degen graduated from…

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