How many clues may appear in one eye during the Horizontal Gaze Nystagmus (HGN) test?

The Horizontal Gaze Nystagmus (HGN) test is a key indicator used by law enforcement to assess potential impairment due to alcohol or drugs. During this test, officers look for specific clues of nystagmus—an involuntary eye movement—while observing the eyes as they follow a stimulus, such as a pen or flashlight.

In this context, three distinct clues may appear in each eye, which allows officers to evaluate the level of impairment. These clues include: (1) the inability to smoothly follow the stimulus, (2) the presence of distinct nystagmus at maximum deviation (when the eye is at the farthest point to the side), and (3) the onset of nystagmus prior to a 45-degree angle from the centerline of the gaze.

The significance of identifying these three clues in each eye is that they contribute to determining whether a driver is likely under the influence. Recognizing all three in one eye increases the likelihood of impairment and assists in establishing the need for further testing or intervention.