It causes weakness or paralysis of the superior oblique muscle that it innervates.

This condition often causes vertical or near vertical double vision as the weakened muscle prevents the eyes from moving in the same direction together.

To compensate for the double-vision resulting from the weakness of the superior oblique, patients characteristically tilt their head down and to the side opposite the affected muscle.

When present at birth, it is known as congenital fourth nerve palsy.

This article about a medical condition affecting the nervous system is a stub.