BPOC SFST Practice Test 2025 – Complete Prep Guide

The presence of jerking of the eyes, specifically during the Horizontal Gaze Nystagmus (HGN) test, is a significant indicator of impairment. HGN is a test used by law enforcement to assess a person's ability to track a moving object smoothly with their eyes. When a person is sober, their eyes should follow the stimulus smoothly. However, impairment from substances like alcohol can cause involuntary jerking or jerking of the eyes, known as nystagmus, which becomes noticeable when the eyes are moved to the side at certain angles.

This involuntary jerking suggests a disruption in the normal functioning of the central nervous system, aligning with the effects of alcohol or other drugs. Consequently, the presence of eye jerking observed during the test provides critical evidence that the individual may be under the influence.

In contrast, the other options do not directly indicate impairment in the same way. Being able to follow directions, exhibiting a steady focus, and the ability to maintain balance are not clear indicators of intoxication. In fact, those traits could suggest that the individual is sober, as impaired individuals may struggle with following directions, focusing, or maintaining physical stability. Thus, jerking of the eyes is the unequivocal clue indicating impairment during the