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Nystagmus Tests

What is Nystagmus for DUI roadside tests?

Horizontal Gaze Nystagmus (HGN) Testing is a field sobriety test recognized by the National Highway Traffic & Safety Administration (NHTSA). The HGN test involves the police officer having the driver follow a pen (or any "stimulus") with his eyes. The police officer is looking for specific responses from the eyes (nystagmus) that show the driver is under the influence.

Nystagmus is the involuntary rapid movement of an eye either horizontally or vertically. It can be brought on by disease, head trauma, and many other physiological conditions. (See our article on Nystagmus Causes). Alcohol consumption also causes this condition.

How is the HGN test conducted?

To conduct the test, the police officer will hold a pen or finger approximately 12 inches from the driver's face at eye level and move it back and forth parallel to the ground in front of the driver. The police officer is looking for three clues,  (1) lack of smooth pursuit, (2) onset of nystagmus before 45 degrees, and (3) distinct nystagmus at maximum deviation. Each of the above three indicators counts as one point in the test and a total of four points is considered as indication of impairment.

Is the HGN test admissible in Georgia courts for evidence of DUI?


The results of the HGN may be excluded from evidence where it is shown that the test was not performed according to standards accepted by NHTSA. A health condition affecting the eyes such as an astigmatism or lazy eye can cause the results to be inaccurate. A trained Georgia DUI lawyer can challenge an incorrectly performed DUI test and exclude it from evidence. 

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