The trochlear nerve, also known as cranial nerve IV, is one of the twelve pairs of cranial nerves in the human body. It is primarily responsible for controlling the movement of the superior oblique muscle, which helps rotate the eye downward and laterally. This nerve is unique because it is the only cranial nerve that emerges from the dorsal aspect of the brainstem. The trochlear nerve is small and has a long course, making it susceptible to injury. Damage to this nerve can lead to double vision and difficulty with eye coordination, particularly when looking down. Proper functioning of the trochlear nerve is essential for normal visual tracking and depth perception.