What is defined as an involuntary oscillation of the eyeball?

Nystagmus is characterized by an involuntary oscillation or rhythmic movement of the eyeballs. This condition can be caused by various factors, including neurological disorders, inner ear problems, or even congenital issues, and it can manifest in side-to-side, up-and-down, or even circular movements of the eyes. The involuntary nature of these oscillations distinguishes nystagmus from other eye conditions, emphasizing its relevance in the context of eye movement disorders.

Keratoconus, on the other hand, is a condition related to the shape of the cornea rather than eye movement. It involves a progressive thinning and cone-like bulging of the cornea, which can affect vision but does not lead to oscillation of the eyeball. Aniridia refers to the absence of the iris, which impacts the appearance and function of the eye but does not involve any oscillatory movement. Astigmatism is an optical defect that results from an irregular curvature of the cornea or lens, leading to blurred vision, yet it also has no relation to involuntary eye motions.