A reader recently wrote to medical experts at UCLA Health after experiencing an episode in which their left eye felt out of alignment and they were unable to focus. Although a brain scan did not reveal any issues, the individual was diagnosed with cranial nerve IV palsy, also known as trochlear nerve palsy. The doctor attributed the condition to a concussion that occurred last spring.
According to UCLA Health, “You have been diagnosed with a condition known as cranial nerve IV palsy. It causes weakness or paralysis of the nerve that animates the muscle responsible for moving the eye downward and inward toward the nose. The Roman numeral in the name refers to the fourth cranial nerve, also known as the trochlear nerve. The word ‘palsy’ indicates limited or impaired movement. The medical term for this condition is trochlear nerve palsy.”
The human body contains 12 cranial nerves, each serving different functions. The third, fourth, and sixth cranial nerves control eye movement through six muscles. For the fourth cranial nerve, its function involves controlling the superior oblique muscle, which moves the eye downward and inward toward the nose and helps move it outward as well.
Damage to this nerve can interfere with signals sent to the superior oblique muscle, leading to vision problems such as those described by the patient. Trochlear nerve palsy may be congenital (present at birth) or acquired due to injury. Its long path through the skull makes it especially vulnerable during head trauma.
Symptoms include misalignment of vision, inability to focus, double vision—often worse at night—dizziness when looking down, a need to tilt one’s head for clarity, and crossed eyes. Diagnosis is based on symptoms and vision tests; treatment depends on what caused the problem.
UCLA Health states: “It is possible that you will have another episode. However, the good news is that when trochlear nerve palsy results from an injury, it often resolves on its own, typically in six to eight months.” During recovery, patients may be prescribed prism glasses—special eyewear designed with wedge-shaped lenses that help correct misalignment—or an eye patch if needed.
If symptoms persist beyond eight months without improvement from these measures, surgery may be considered to realign the eyes.
Readers seeking more information or wishing to schedule an appointment can contact UCLA Health through their online booking options or by mail at Ask the Doctors c/o UCLA Health Sciences Media Relations.
