An involuntary, repetitive, and rhythmic movement of the eyes characterized by alternating slow and fast phases. It can occur in a horizontal, vertical, rotary, or combined pattern. Nystagmus may be congenital, appearing in infancy, or acquired later in life due to vestibular disorders, neurological conditions, medications, or toxins. It can affect visual acuity, depth perception, and balance. Treatment depends on the underlying cause and may include corrective lenses, medications, or surgery in some cases.