What is it?

The fourth cranial nerve controls the actions of one of the external eye muscles, the superior oblique muscle.
Diseases or injuries to the fourth cranial nerve can cause the superior oblique muscle to be paralyzed. The name for this condition is fourth nerve palsy. Other names for it are superior oblique palsy and trochlear nerve palsy.
You may have fourth nerve palsy from birth, or you may develop it later. It usually happens in only one eye, but it can also occur in both.

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Additional names

This group contains additional names:
- Trochlear nerve palsy
- Trochlear dysplasia

Signs & symptoms

Double vision (diplopia) is a common symptom of fourth nerve palsy. It only occurs when both eyes are open. With one eye shut, you see one image. But when you open both eyes, you may see two images. One of the images may appear to be above the other, or above and to the side of the other. For some people, one image may appear slightly turned compared with the other. If there is little separation between images, the overall image may appear blurry instead of double.

Other symptoms may include:
* One iris higher than the other. The iris is the colored part of your eye.
* Holding your head at a tilt. This is to help with the vision problem.
* Pain, usually above the eyebrow. This can happen if the fourth nerve palsy is idiopathic or related to diabetes.
If you have had the palsy for a while, your brain may have started to ignore images from that eye. If this is the case, you may not have double vision.


The doctor will probably take a health history, asking you about your recent symptoms and your past health information. The doctor can check the cranial nerves by doing a medical exam. They will look at the position of the eyes at rest and then have you follow an object with your eyes. The doctor may also check how the pupils react to light, measure the pressure in your eye, and look at the backs of your eyes. They may ask to look at old photos of you to try to find out when the problem started.

Several other conditions can cause double vision. The doctor may order tests to help tell fourth nerve palsy from other conditions. These may include:
* Blood tests, to look for autoimmune diseases and thyroid hormone levels
* CT scan or MRI, to look at your brain and cranial nerves
* Ultrasound, to look at the muscles of the eye
* Spinal tap (lumbar puncture), to look for causes of increased intracranial pressure
* Nerve stimulation tests
The doctor may send you to an eye doctor (ophthalmologist) for diagnosis and to manage your condition. You may even need to see a neuro-ophthalmologist. This is an eye doctor with special training to treat nerve problems of the eye.


Treatment of fourth nerve palsy depends on its cause. Idiopathic fourth nerve palsies tend to go away on their own. Palsies caused by injury can also get better with time. If something is pressing on the fourth cranial nerve, you may need surgery to ease the pressure.

Possible treatment of fourth nerve palsies include:
* Over-the-counter pain medicines
* Prism glasses- These can bring the double images together as one image.
* Eye patch- You switch this from one eye to the other so that one eye doesn’t get weak or lazy.
* Surgery to realign the eyes
The goal of surgery is to get rid of the double vision. This can also correct the tendency to tilt your head. You may need surgery on both eyes if the eye problem is severe.

☝️ This is not a substitute for professional medical advice. Please consult with your physician before making any medical decision.

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