This video shows the cranial nerve palsies that affect the eye … specifically third nerve palsy, fourth nerve palsy, and sixth nerve palsy. You can watch this presentation in full screen and high-definition by clicking the appropriate buttons. If you have problems you can also watch directly at
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SuperPalsies.m4v (234 mb)
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The rectus muscles attach to the eye and control the basic eye movements such as looking up/down and left/right.
The oblique muscles attach toward the back of the eye and allow the eye to rotate side to side. The superior oblique muscle on top is particularly important as it is innervated by the fourth cranial nerve.
When the third nerve stops working, the eye looses innervation to most of the extraocular muscles. This causes the eye to drift down and outwards. Also, the levator muscle stops working and so the upper eyelid droops. Finally, the parasympathetic nerves that run along with the third nerve stop working, causing the pupil to dilate.
A 3rd nerve palsy has specific pattern … a down and out eye, combined with a droopy eyelid and blown pupil. The underlying differential is extensive, but tends to be from vasculopathic problems (diabetes and hypertension), tumor, or aneurysm.
The parasympathetic fibers run along the outside of the third nerve. Compressive lesions (such as an aneurysm) tends to push on these fibers and cause the pupil to blow. This is in contrast to deeper ischemic nerve damage, which may leave the parasympathetics intact.
The 6th cranial nerve (abducens nerve) innervates the lateral rectus muscle. When this stops working, the eye turns inward and has a difficult time moving outwards (abducting).
Sixth nerve palsies are easy to diagnose. The cause is much harder, however. Most of these palsies are caused by vasculopathic problems (diabetes and hypertension). Tumor is another possibility. We also occasionally see a 6th palsy with increased intracranial pressure … also known as pseudotumor cerebri.
The brain sits suspended in the skull, floating in CSF (cerebrospinal fluid). The fluid pressure can increase and cause neurologic symptoms. Something about the sixth nerve anatomy makes it predisposed to disfunctioning with high intracranial pressure.
The fourth cranial nerve has a long course and innervates only a single muscle … the superior oblique.
The superior oblique runs through a trochlea or “pully” that effectively changes the functional origin of the muscle. To simulate the action of the superior oblique muscle, you can pretend that your head is a giant eyeball. Simply wrap your hand behind your head and pull. The direction of eye movement changes depending upon which direction you look. When the eye (your head) is turned nasally (toward your elbow) you get more up-down movement. When the eye is turned outwards, the muscle creates more of a side-to-side rotational action.
When the fourth nerve is damaged, the eye has a tendency to shoot upwards when looking nasally. This is called a “nasal upshoot.”
There are many causes for a 4th nerve palsy. Like the other cranial nerves, vasculopathic problems like diabetes and hypertension are common. Tumor can also cause a palsy because the fourth nerve has a long course through the cranial vault. Congenital palsies are common in children and often overlooked because children learn to adapt with a head tilt. Trauma can also cause a palsy because of the long and skinny nerve.
With vasculopathic nerve damage, the underlying structure of the peripheral nerve is still intact. This allows the axons to regrow over time … typically 3-6 months for the cranial nerves.
If the nerve is damaged from trauma or a mass lesion (or aneurysm) the nerve structure is damaged. This can lead to aberrant regeneration as the axons become confused and can inappropriately connect to the wrong muscles.
Third nerve palsies make the eye turn down and outwards. A blown pupil is troubling, as it may imply a compressive lesion such as aneurysm.
A sixth nerve palsy makes the eye turn inward, such as with this patient’s right eye. You can sometimes detect an ocular alignment problem by examining the corneal light reflex.
Fourth nerve palsies are difficult to check. They cause a nasal upshoot … the eye turns upwards when looking toward the nose. While this may be obvious in this snapshot, in reality a 4th palsy is tricky to detect.
Temporal arteritis (also known as giant cell arteritis) is an inflammatory disorder where blood vessels in the face and brain become inflamed. This inflammation can get so bad that an artery actually blocks up entirely, causing an instant palsy or paralysis to a cranial nerve, retina, or even brain (i.e.. stroke). Prodrome symptoms include scalp tenderness, jaw claudication (pain with chewing), polymyalgias (muscle aches), weight loss, fatigue, and night sweats. Temporal arteritis should be considered in people over the age of 60-65 year of age with a new palsy. Workup includes labwork (ESR, CRP, platelets) and potentially temporal artery biopsy in certain cases.
Increased intracranial pressure (ICP) can manifest as papilledema, swelling of the optic nerves in the back of the eye. This can be seen during a dilated retina exam.
Increased cranial pressure can cause a 6th nerve palsy. Some believe that the twisting course of the 6th nerve makes it more susceptible to pressure damage.
The maddox rod can be used to pick up vertical alignment problems. When held in front of the eye at this angle, the patient will see a red horizontal line in their vision.
If both eyes are in good vertical alignment, the red line from the right eye, and the white light from the left, should be touching.
If the red line is described as being located “below the light” … this means the right eye is deviating upwards.
Unlike the other cranial nerves, the fourth nerve comes out the BACK of the brainstem. The nerve is also very long and skinny. For these reasons, the 4th nerve is susceptible to damage from trauma.
This is a test used to look for ocular alignment problems. You hold a prism (base-up or base-down) and see how much vertical prism your patient can handle before developing double vision. Most people can only handle one or two diopters of prism before getting double vision or eye strain. If your eyes have been out of alignment for a long time (such as from a congenital 4th nerve palsy) then you may be able to handle a LOT of prism before experiencing double vision. This implies that the alignment issue has been there for a long time.