Why is it important to evaluate the onset of nystagmus at a specific angle?

Evaluating the onset of nystagmus at a specific angle is crucial for assessing the level of alcohol impairment in an individual. Nystagmus refers to the involuntary eye movement that can indicate impairment when a person has consumed alcohol or other substances. By observing the angle at which nystagmus begins, law enforcement officers can gather evidence regarding the degree of impairment. If nystagmus is detected at 45 degrees or earlier, it typically suggests a higher level of intoxication. This measurement is a key component of the Horizontal Gaze Nystagmus test, which is used to help establish whether a driver is under the influence of alcohol, thereby aiding in the determination of their fitness to operate a vehicle. The onset angle is a critical factor that enhances the reliability of this assessment.