Final answer:
Rapid movement of the eyeball is known as nystagmus, which is characterized by quick, involuntary movements of the eyes in various directions.
Step-by-step explanation:
Rapid movement of the eyeball is known as nystagmus. This condition involves quick, involuntary movements of the eyes, which can be horizontal, vertical, or rotary. It's distinct from the concept of saccadic eye movements, which are rapid and conjugate movements of the eyes used to survey a visual stimulus or follow a moving object.
Hyperopia, also referred to as farsightedness, is a condition where the eyes focus light behind the retina, causing nearby objects to appear blurry. Presbyopia, on the other hand, is an age-related condition where the eyes struggle to focus on close objects due to less elasticity of the lens or weakening of the associated muscles.
Hordeolum, commonly called a stye, is an infection of the oil glands in the eyelid. Therefore, the correct answer to the aforementioned question is A. nystagmus.