What is the third clue in the HGN test?

The third clue in the Horizontal Gaze Nystagmus (HGN) test is the onset of nystagmus prior to 45 degrees. This aspect of the test is crucial because it indicates that the eyes are exhibiting involuntary jerking movements, which can be a sign of impairment, particularly from substances like alcohol.

During the HGN test, an officer assesses the eyes of the subject as they follow a stimulus, typically a pen or finger, moving horizontally. The angle at which the nystagmus begins—specifically before reaching 45 degrees—suggests a potential level of impairment, as a sober person typically displays nystagmus beyond this angle. Therefore, this clue serves as an important indicator of the subject's ability to maintain visual coordination and control, which can be compromised by intoxication or drug influence.

The recognition of this specific behavior aids officers in making informed decisions during sobriety evaluations, as the presence of this sign can play a significant role in determining whether further evaluation or action is warranted.