Final answer:
The correct option is C. nystagmus. The involuntary, rhythmic movement of the eyes is called nystagmus, which is different from dysphagia, hyperopia, or anisocoria. Nystagmus can be part of normal eye movement or indicate an underlying condition.
Step-by-step explanation:
The involuntary, rhythmic movement of the eyes that is being referred to in the question is known as nystagmus. This condition can occur as a normal reflex, or it might signal a problem with the inner ear, brain, or ability of the eyes to maintain a stable position. While dysphagia refers to difficulty swallowing, hyperopia denotes farsightedness, and anisocoria is characterized by unequal pupil sizes, nystagmus specifically describes the eye movements in question.
Testing eye movement can involve having a patient follow an object with their eyes, which checks for the proper function of the eye muscles and neural pathways, including the medial longitudinal fasciculus (MLF). Failures in conjugate eye movement can lead to conditions like internuclear ophthalmoplegia, which might result in diplopia or double vision. The accommodation-convergence reflex is another aspect of eye function, coordinating eye muscle movement with the lens's ability to focus on near objects, which is particularly relevant as a person ages and might need corrective lenses.