How accurate is the horizontal gaze nystagmus test?

 Posted on March 02, 2024 in DUI Charges

When Maryland drivers are stopped by police and suspected of being intoxicated, officers will usually ask to administer several field sobriety tests. The horizontal gaze nystagmus (HGN) is one of three standardized field sobriety tests that officers often administer to evaluate impairment. However, like all field sobriety tests, the horizontal gaze nystagmus test is not 100% accurate. 

What is horizontal gaze nystagmus? 

Horizontal gaze nystagmus is a medical term that describes the involuntary jerking of the eyeballs. When a person is intoxicated, this jerking in the eyes becomes more prominent and noticeable. Before administering the HGN test, the officer is supposed to examine the individual’s eyes to gauge their resting nystagmus, pupil size and tracking to see if both eyes can follow an object together. 

Administering the horizontal gaze nystagmus test 

To administer an HGN test, the officer will hold a small object, usually an ink pen, about 12-15 inches from the individual’s nose. The officer will then move the object slowly from one side to the other. The individual will attempt to follow the object with their eyes while keeping their head still. The officer looks for any jerking or bouncing in the eyes and will also look for nystagmus before the eyes get to a 45-degree angle. 

Options for DUI defense 

As mentioned earlier, the HGN test is not completely accurate. Reportedly, studies done by the National Highway Traffic Safety Administration found that the HGN test is only around 77% accurate. Many times, officers do not administer these tests correctly and certain pre-existing medical conditions can also affect test results. Those in Maryland who are arrested and charged with DUI have the right to an attorney. A seasoned attorney can assess the situation, protect individual rights and determine the best possible defense strategy.