The trochlear nerve is one of 12 sets of cranial nerves. It is part of the autonomic nervous system, which innervates many of your organs, including the eyes.
This nerve is the fourth set of cranial nerves. It is a motor nerve that sends signals from the brain to the muscles. Fourth cranial nerve works with the oculomotor nerve and other eye muscles to control eye movements.
It enables movement in the eye’s superior oblique muscle. This makes it possible to look down. The nerve also enables you to move your eyes toward your nose or away from it.
The trochlear nerve gets its name from the Latin word pulley, “trochleae.” A pulley is a device that lifts an object.
In each eye, the superior oblique muscle functions as the trochlea. The trochlear nerve innervates this muscle to lift the eyes so you can look down. The nerve also enables you to move your eyes toward your nose or away from it.
When the trochlear nerve doesn’t function as it should, it’s often due to fourth nerve palsy. The condition is called trochlear nerve palsy. A palsy occurs when illness or injury paralyzes nerves that control muscle movement.
In some people, it’s congenital, meaning they are born with this condition. It may also be due to trauma from rapid head movements, like during motor vehicle accidents. The trochlear nerve is one of the more fragile cranial nerves because it’s thin and long. Cranial nerve palsy sometimes occurs after minor injuries.
Less common causes include:
The treatment that’s right for you depends on what’s causing your symptoms. For vision issues due to minor injuries, symptoms often go away on their own.
For more severe injuries or palsies due to medical conditions, your care may include:
Contact your eye specialist if you experience symptoms of trochlear nerve palsy. They often include vision changes that worsen when you look down. These include blurry or double vision.
Tilting your head up and to the side may help you compensate for the vision changes. But this posture strains neck muscles and can become painful.
Other concerning symptoms that need medical attention include:
The trochlear nerve is fragile. Protecting your head from injury can help keep your trochlear nerve safe. Minor head injuries and more severe ones from trauma can cause fourth nerve palsy. This condition can cause double vision, crossed eyes and more. Depending on the cause, symptoms may go away on their own. Some people need special glasses or surgery.
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