What does a jerking motion in the eyes during HGN test indicate?

The jerking motion in the eyes, known as nystagmus, during the Horizontal Gaze Nystagmus (HGN) test is a key indicator of potential alcohol impairment. When an individual is under the influence of alcohol, it affects the central nervous system and can result in eye movements that are not smooth. The HGN test involves observing the eyes as they follow a stimulus, and the presence of nystagmus at certain angles—specifically, as the eye reaches a maximum deviation—can suggest that the person's blood alcohol concentration may be above legal limits, typically around 0.08%.

In contrast, high anxiety levels may cause some physical responses, but they do not specifically cause the jerking motion associated with HGN. Similarly, fatigue may lead to a lack of coordination, but it also typically doesn’t produce the distinct pattern of eye movement seen in the HGN test. Disinterest in the test might result in poor performance, but it won’t cause the physiological response of nystagmus that indicates impairment due to alcohol. Hence, the presence of a jerking motion in the eyes is most reliably linked to potential alcohol impairment.