Which cranial nerve is associated with the ability to move the eye downward?

The trochlear nerve is primarily responsible for the downward movement of the eye, specifically controlling the superior oblique muscle. This muscle plays a crucial role in allowing the eye to move downward and laterally, which is vital for facilitating complex visual tasks and coordinating movement when looking downwards, such as when reading or descending stairs.

The strength of the trochlear nerve's function can be observed when executing these downward eye movements; a dysfunction can lead to difficulty with those actions, such as vertical diplopia or misalignment in vision. The other cranial nerves listed do involve eye movement but do not specifically focus on the downward motion as the trochlear nerve does.