What is the purpose of the "nystagmus" test in field sobriety tests?

The nystagmus test is specifically designed to observe the involuntary jerking of the eyes, which is often a sign of alcohol impairment. When a person consumes alcohol, it can impact their body’s nervous system, leading to impaired control of eye movements. During the test, law enforcement officers typically check for specific characteristics of nystagmus, such as how smoothly the eyes track a moving object and any noticeable jerking that occurs, especially when the eyes are held at certain angles.

Identifying this involuntary eye movement helps officers assess whether a driver may be under the influence of alcohol. Research has shown that the presence of nystagmus can correlate with higher blood alcohol concentration levels, making it a reliable indicator of potential impairment. Therefore, its purpose within a field sobriety context is rooted in assessing a driver’s physical and neurological responses to alcohol rather than evaluating strength, memory, or documentation status.