Your eye is made up of three nerves that control the movement of your eyes, the location of your eyelids, and the size of your pupils. These nerves are the oculomotor nerve, the trochlear nerve, and the abducens nerve. They are also known as the third cranial nerve, the fourth cranial nerve, and the sixth cranial nerve respectively.
The actions of the superior oblique muscle, also known as the external eye muscle, are controlled by the fourth cranial nerve. The superior oblique muscle is located in the back of the eye socket. It runs along the top of the eye and passes through a loop of tissues located alongside the nose. These tissues are known as trochlea. The superior oblique muscle allows the eye to be turned downward and inward.
When the fourth cranial nerve is injured or diseased, it can cause paralysis of the superior oblique muscle. This is known as superior oblique palsy, trochlear nerve palsy, or fourth nerve palsy.
Some individuals are born with this condition while others develop it later on in life. It usually affects just one eye.
Superior Oblique Palsy Causes
Most adolescents are born with superior oblique palsy. When present from birth, it is referred to as congenital fourth nerve palsy.
Adults are commonly diagnosed with superior oblique palsy after sustaining an injury. Though the injury may seem minor to the individual in question, it can still result in this condition. In fact, even conditions such as whiplash or concussions can lead to superior oblique palsy developing. If an injury causes superior oblique palsy to form, it might never heal.
Diabetic individuals are also at an increased risk of developing superior oblique palsy due to their poor blood circulation.
More often than not, though, there is no known cause of fourth nerve palsy. When there is no known cause, the condition is referred to as idiopathic fourth nerve palsy. Many adults have this type of fourth nerve palsy. Oftentimes, idiopathic fourth nerve palsy goes away on its own.
Some other common causes of superior oblique palsy include:
Superior Oblique Palsy Symptoms
The most common symptom of superior oblique palsy is diplopia (double vision). This visual distortion occurs only when both eyes are open and disappears when one eye is closed. When those affected see two images, one image may look as though it is floating above the other one. Sometimes, though, there isn’t much separation between the two images, so you may not see two images apart from one another and will instead just see one blurry image.
Other symptoms of superior oblique palsy include:
- One iris that is higher than the other
- A tilted head to compensate for vision problems
- Pain located above the eyebrow, more common in cases of idiopathic fourth nerve palsy or diabetes
Some individuals may not experience double vision, though. This is especially true for individuals who have had fourth nerve palsy for a while.
When congenital superior oblique palsy occurs at birth, there are usually subtle symptoms that occur alongside it. These symptoms gradually increase as the child ages.
Because there are rarely symptoms present at birth, congenital superior oblique palsy may not be diagnosed until late childhood or even early adulthood. This usually depends on the severity of the condition. Additionally, double vision usually does not occur in congenital cases, though a head tilt may still be present.
Diagnosing Superior Oblique Palsy
First, your doctor will check your health history. They will ask you questions regarding any recent symptoms you have experienced, as well as any past health information. A medical exam will be performed in order to examine your cranial nerves. Your eyes will be examined: Your doctor will look at them while they are resting as well as when they are following an object. A pupil test may also be conducted, as well as tests to measure the pressure in your eyes and to observe the backs of your eyes.
Your doctor may also ask to see photos of you from years before to try and determine when the condition first began. Since many other conditions can result in double vision occurring, your doctor may order additional tests to help determine whether you have fourth nerve palsy or another disease.
The tests your doctor performs could include:
- Blood tests. These can check for autoimmune disorders and ensure that you have proper thyroid hormone levels.
- CT scans or MRIs. These tests can help your doctor view your brain and cranial nerves.
- Ultrasound. An ultrasound can help examine the eye muscles.
- Spinal tap. Also known as a lumbar puncture, this test is done to look for the cause of increased intracranial pressure.
- Nerve stimulation tests. These tests will test your nerves and how they react.
In addition to these tests, your doctor may refer you to an ophthalmologist (eye doctor) for a proper diagnosis and treatment.
Superior Oblique Palsy Treatment
How superior oblique palsy is treated will depend on the cause and the severity. Some superior oblique palsies tend to go away on their own. This is often the case with idiopathic fourth nerve palsy. Palsies that are a result of injuries may also improve over time, though in other cases they do not go away at all.
Surgery might be required in cases where there is pressure on your fourth cranial nerve. Otherwise, other possible treatments include:
- Over-the-counter pain medications
- Prism glasses, which can help with double vision
- An eye patch, which can also help with double vision
- Surgery that can realign the eyes
Superior Oblique Palsy Complications
Living with superior oblique palsy doesn’t have to be difficult. It usually has few complications. If this condition does not resolve on its own, it may simply change how your eyes work together.
Children with this condition are susceptible to a change in how their face looks, though. This is a concern, especially for children who present a head tilt. In cases where a head tilt is present, muscles on one side of the face will not develop the same as the muscles on the other side. This leads to the face appearing different over time.
With the right treatments or even surgery, however, you and your child can live a life unaffected by these complications.