What is a Cranial Nerve Palsy?
Nerve palsies occur when blood flow to a specific nerve is blocked. Numbness and tingling down your leg when sitting too long is a very temporary nerve palsy.
Nerve palsies can occur in both the peripheral nervous system (e.g. arms and legs) but also in the central nervous system, such as your brain.
There are 12 pairs of cranial nerves in the back of the brain. They send and receive signals between your face, neck, and torso. These nerves each have a specific function:
- Olfactory nerve: Sense of smell
- Optic nerve: Ability to see
- Oculomotor nerve: Ability to move and blink your eyes
- Trochlear nerve: Ability to move your eyes up and down
- Trigeminal nerve: Sensations in your face and cheeks, taste and jaw movements
- Abducens nerve: Ability to move your eyes
- Facial nerve: Facial expressions and sense of taste
- Auditory/vestibular nerve: Sense of hearing and balance
- Glossopharyngeal nerve: Ability to taste and swallow
- Vagus nerve: Digestion and heart rate
- Accessory nerve (or spinal accessory nerve): Shoulder and neck muscle movement.
- Hypoglossal nerve: Ability to move your tongue
If blood flow to one of these nerves is reduced or blocked, or if the nerve is damaged by a head trauma or infection, then the muscles that respond to the impulses from these nerves cannot function properly. When this occurs, it is called a palsy.
A palsy to the 3rd, 4th, and 6th cranial nerves affects the eyes. Each of the palsies of these three nerves are discussed below. Damage to the optic nerve (glaucoma) is not discussed in this article.
What causes cranial nerve palsy?
A cranial nerve palsy can be present at birth, caused by trauma, or due to blood vessel disease (hypertension, diabetes, strokes, aneurysms, etc.). It can also be caused by viral infections, migraines, tumors, or elevated intracranial pressure.
The most common causes are:
- Birth trauma
- Head injury
- Viral infection
- Brain tumor
Third cranial nerve palsy
A palsy of the third cranial nerve is known as “oculomotor nerve palsy” and occurs when the 3rd cranial nerve is damaged by disease or injury. The 3rd cranial nerve controls the action of the four external eye muscles. Those muscles move the eye upward and downward, they rotate the eye outward toward the ear and they turn the eye inward.
Symptoms of third nerve palsy include:
- An enlarged pupil that does not react normally to light
- Double vision (diplopia)
- Droopy eyelid (ptosis)
- Eye misalignment (strabismus)
- Tilted head to compensate for binocular vision difficulties
Fourth cranial nerve
A palsy of the fourth cranial nerve is called “superior oblique palsy” and it affects the muscle that turns the eye upwards and downwards. The most common symptom of superior oblique palsy is double vision that occurs only when both eyes are open and disappears when one eye is closed.
Sixth cranial nerve palsy
This is the most common type of cranial nerve palsy in adults and the second-most common in children. The 6th cranial nerve sends signals to the muscle that moves the eye outward, away from the nose.
Common symptoms and signs of 6th cranial nerve palsy:
- The eye may turn inward
- Inability to move the eye outward, away from the nose
- Horizontal double vision
- Turning of the head to the side in order to avoid the double vision
Tests used to diagnose cranial nerve palsies
- Neurological exam to test sensation, reflexes, balance and mental status
- Electromyography (EMG) to measure the electrical activity of the muscles when working and at rest
- CT or MRI scans
- Nerve conduction tests to help find out where the nerve is damaged
- Biopsies of the skin and nerves to find out how severely nerves are damaged
- Angiography, a type of X-ray that uses contrast dye and takes pictures of your heart and blood vessels.
Treatments for cranial nerve palsies
Often the palsies will get better without any treatment. In some cases, medicines are used to treat an infection, help reduce swelling in or near a nerve, or ease pain if the palsy is causing pain or discomfort. In some cases, surgery may be needed. Other times, the nerve damage can’t be treated or repaired.
Other treatments that may be used are:
- Vision therapy
- Patching one eye to improve binocular vision
- Prism lenses to reduce or eliminate double vision
It is important to diagnose and treat any health conditions that are causing the nerve palsies, such as high blood pressure, infections, and diabetes. Eating nutritious foods, avoiding smoking, and limiting alcohol can also be beneficial.
Gregory Scimeca, M.D.
Ophthalmologist and Medical Director
The Eye Professionals