A palsy of the 6th cranial nerve impairs the ability to turn the eye outward.
Sixth cranial nerve palsy has many causes, including damage to small blood vessels by diabetes, but the cause is often unidentified.
The affected eye cannot turn fully outward and may turn inward when people look straight ahead.
Doctors can identify 6th cranial nerve palsy based on the symptoms, but tests, including brain imaging, are done to try to identify the cause.
Sixth cranial nerve palsy usually resolves whether the cause is identified or not.
(See also Overview of the Cranial Nerves.)
Palsy refers to paralysis, which can range from partial to complete.
Many disorders can cause this palsy
Diabetes when it damages small blood vessels in the eyes
Head injuries
Tumors
Multiple sclerosis
A bulge (aneurysm) in an artery in the skull
Brain infections, such as meningitis, a brain abscess, or a chronic fungal infection
Complications of an ear or eye infection
Bleeding within the brain
Blockage of an artery supplying the nerve, as can result from diabetes, a stroke, a transient ischemic attack, or vasculitis (inflammation of blood vessels)
Wernicke encephalopathy (commonly due to chronic alcoholism)
Idiopathic intracranial hypertension (pseudotumor cerebri)
Sometimes high blood pressure
Rarely, upper respiratory infections (in children)
Some of these disorders, such as tumors and brain abscesses, increase pressure within the skull and put pressure on (compress) the nerve. Other disorders, such as a blocked artery, interfere with blood flow to the nerve.
If 6th cranial nerve palsy occurs alone (without other cranial nerve palsies), its cause is often never identified.
