Nystagmus can be defined as what phenomenon?

Nystagmus is characterized by involuntary jerking or movement of the eyes, often occurring in a rhythmic pattern. This phenomenon can manifest in various forms, such as horizontal or vertical movements, and is typically a result of disturbances in the vestibular system, neurological conditions, or other medical issues. Understanding nystagmus is crucial in various fields, including medicine and law enforcement, as it can indicate impairment or alcohol intoxication during field sobriety tests.

The other options describe phenomena that do not accurately encapsulate the nature of nystagmus. While voluntary jerking of the eyes implies conscious control over eye movements, nystagmus is an involuntary condition. Loss of focus and blurred vision relate to the clarity of the visual image but do not describe the specific movement characteristics inherent to nystagmus. Therefore, the definition as involuntary jerking is the most precise and aligns with the clinical understanding of the term.