What is the primary purpose of using HGN in DUI testing?

The primary purpose of using Horizontal Gaze Nystagmus (HGN) in DUI testing is to identify signs of alcohol impairment through eye movement. HGN is based on the scientifically established correlation between eye movement patterns and blood alcohol concentration (BAC). When an individual is intoxicated, the smooth pursuit of the eyes can be disrupted, leading to involuntary jerking or nystagmus.

During the HGN test, law enforcement officers carefully observe the eyes as they follow a stimulus, typically a pen or flashlight, moved horizontally. The presence of specific indicators, such as the angle at which the nystagmus begins and the degree of eye jerkiness, can provide evidence suggestive of alcohol impairment. This method is a reliable tool in assessing a driver's level of impairment, as it is specifically designed to evaluate the effects of alcohol on the central nervous system as it relates to eye movement.

Other options focus on unrelated aspects such as physical illness, determining identity, or assessing driving skills, which do not directly pertain to the function of HGN in evaluating impairment specifically due to alcohol consumption.