These palsies can occur when pressure is put on the nerve or the nerve does not get enough blood.
People have double vision when they look in a certain direction, the eyelid droops, and the pupil may be widened (dilated).
Doctors do a neurologic examination and magnetic resonance imaging (MRI) or computed tomography (CT) of the brain.
Treatment depends on the cause.
(See also Overview of the Cranial Nerves Overview of the Cranial Nerves Twelve pairs of nerves—the cranial nerves—lead directly from the brain to various parts of the head, neck, and trunk. Some of the cranial nerves are involved in the special senses (such as seeing... read more .)
Palsy refers to paralysis, which can range from partial to complete.
The most common causes of 3rd cranial nerve palsy are
Pressure on (compression of) the nerve
Inadequate blood flow to the nerve
Compression tends to result from serious disorders, such as
A bulge (aneurysm Aneurysms of Arteries in the Arms, Legs, and Heart An aneurysm is a bulge (dilation) in the wall of an artery. (See also Aortic Branch Aneurysms and Brain Aneurysms.) Aneurysms may occur in any artery. Aneurysms are most common in the aorta... read more ) in an artery supplying the brain
A disorder that causes herniation of the brain Herniation: The Brain Under Pressure
Herniation occurs when the brain is forced downward through a small natural opening in the sheets of tissue that separate the brain into compartments. Herniation may result from bleeding (sometimes caused by a head injury Overview of Head Injuries Head injuries that involve the brain are particularly concerning. Common causes of head injuries include falls, motor vehicle crashes, assaults, and mishaps during sports and recreational activities... read more ), a tumor, or another mass in the brain.
Inadequate blood flow in very small blood vessels that supply the nerve or in larger ones in the brain stem is more common. It typically results from
Other disorders that affect blood vessels, such as a stroke Ischemic Stroke An ischemic stroke is death of an area of brain tissue (cerebral infarction) resulting from an inadequate supply of blood and oxygen to the brain due to blockage of an artery. Ischemic stroke... read more
, a transient ischemic attack Transient Ischemic Attacks (TIAs) A transient ischemic attack (TIA) is a disturbance in brain function that typically lasts less than 1 hour and results from a temporary blockage of the brain’s blood supply. The cause and symptoms... read more , vasculitis Overview of Vasculitis Vasculitic disorders are caused by inflammation of the blood vessels (vasculitis). Vasculitis can be triggered by certain infections or drugs or can occur for unknown reasons. People may have... read more 
(inflammation of blood vessels), or a bulge in an artery (aneurysm Aneurysms of Arteries in the Arms, Legs, and Heart An aneurysm is a bulge (dilation) in the wall of an artery. (See also Aortic Branch Aneurysms and Brain Aneurysms.) Aneurysms may occur in any artery. Aneurysms are most common in the aorta... read more ) that carries blood to the brain
Symptoms of Third Cranial Nerve Palsy
The affected eye turns slightly outward and downward when the unaffected eye looks straight ahead, causing double vision. The affected eye may turn inward very slowly and may move only to the middle when looking inward. It cannot move up and down. Because the 3rd cranial nerve also raises the eyelids and controls the pupils, the eyelid droops. The pupil may be normal or be widened (dilated) and may not narrow (constrict) in response to light, as normally occurs. The pupil is often affected when the cause is compression of the 3rd cranial nerve. When the pupil is not affected, the cause is often inadequate blood flow to the nerve.
Some serious disorders causing the palsy may worsen, resulting in a serious, life-threatening condition. For example, a severe headache may occur suddenly, or a person may become increasingly drowsy or less responsive. In such cases, the cause may be a ruptured aneurysm, which then bleeds, or herniation of the brain Herniation: The Brain Under Pressure . People may go into a coma. In such people, dilation of both pupils and lack of response to light by both pupils indicates deep coma and possibly brain death Brain Death Brain death is the permanent loss of brain activity. As a result, people cannot breathe or maintain other vital functions on their own, and they permanently lose all awareness and capacity for... read more .
Diagnosis of Third Cranial Nerve Palsy
Neurologic examination
Magnetic resonance imaging or computed tomography
Sometimes other tests
The diagnosis of 3rd cranial nerve palsy is based on results of a neurologic examination Neurologic Examination When a neurologic disorder is suspected, doctors usually evaluate all of the body systems during the physical examination, but they focus on the different parts of the nervous system. Examination... read more .
Magnetic resonance imaging (MRI) or computed tomography (CT) of the brain is done to identify the cause.
If the pupil is affected or if symptoms suggest a serious underlying disorder, brain MRI or CT is done immediately.
If a ruptured aneurysm is suspected, CT or, if available, MRI is done immediately. If CT or MRI does not detect blood, a spinal tap Spinal Tap Diagnostic procedures may be needed to confirm a diagnosis suggested by the medical history and neurologic examination. Imaging tests commonly used to diagnose nervous system (neurologic) disorders... read more 
(lumbar puncture), magnetic resonance angiography Magnetic resonance angiography (MRA) Magnetic resonance imaging (MRI) is a type of medical imaging that uses a strong magnetic field and very high frequency radio waves to produce highly detailed images. During an MRI, a computer... read more 
, CT angiography CT angiography Computed tomography (CT) is a type of medical imaging that combines a series of x-rays to create cross-sectional, detailed images of internal structures. In computed tomography (CT), which used... read more 
, or cerebral angiography Angiography Angiography is a type of medical imaging that uses x-rays and a contrast agent to produce images of blood vessels. In angiography, x-rays are used to produce detailed images of blood vessels... read more is done.
Treatment of Third Cranial Nerve Palsy
Treatment of the cause
Treatment of 3rd cranial nerve palsy depends on the cause. Emergency treatment is required if a life-threatening disorder is the cause.
