What does Horizontal Gaze Nystagmus (HGN) test determine?

The Horizontal Gaze Nystagmus (HGN) test is a reliable indicator of impairment, particularly in the context of DUI assessments. This test assesses the involuntary jerking of the eyes as they move from side to side. When an individual is under the influence, this eye movement tends to become more pronounced; thus, the HGN test is used as part of a field sobriety test to evaluate a driver’s level of impairment.

While other options may relate to aspects of sobriety or driving capabilities, the HGN specifically focuses on the eye movements and their relation to impairment. It does not measure alcohol consumption levels directly, nor does it evaluate overall vision or coordination outside of the nystagmus response. Additionally, it does not assess a driver's reaction times, as reaction times involve response speed to stimuli, which is outside the scope of what the HGN is designed to determine. This makes the HGN test a critical component of field sobriety assessments, specifically aimed at gauging impairment in drivers.