What is the Horizontal gaze nystagmus (HGN) Test?
Horizontal gaze nystagmus (HGN) is an involuntary movement or jerking of the eyes as they follow a line or moving object from side to side. Officers will typically ask you to follow their finger or a pen with your eyes only, without moving your head. Allegedly, the more alcohol a person has consumed the sooner and more frequently the eyes will jerk as they follow the line.
The officer administers the test by asking the person to follow the tip of a pen while keeping their head totally still. The police officer looks at how smoothly the eyes move, and how much jerking they are doing as they move until they reach their farthest point, and whether there was any movement of the head. Each of these factors is counted by the officer in each eye. If the police officer counts 4 out of 6, he or she will jump to the only conclusion they know assuming that it is very likely the person taking the test has a BAC above the legal limit.
Important Facts about HGN Tests:
- Highly inaccurate
- Causes of HGN are not solely a result of alcohol consumption. Several factors other than alcohol consumption can cause an involuntary jerking of the eye.
- Officers are neither medical doctors nor ophthalmologists (not experts) thus lack proper training and expertise to provide their opinion based on the test results.
- The results of this test are not inadmissible at trial (New Mexico). The officer may testify as to whether the defendant followed directions (i.e. “Defendant did not follow directions because he moved his head after repeatedly asking Defendant to not move his head and to follow my finger with his eyes only.”)