Cranial Nerve Palsies (Video)


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 Vimeo, Youtube, or download the video file directly to your computer (links below).


SuperPalsies.m4v (234 mb)
SuperPalsies720p.m4v (790 mb)

SCREEN SHOTS  (comments below)

Rectus Muscles
The rectus muscles attach to the eye and control the basic eye movements such as looking up/down and left/right.
Oblique Muscles
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.
Third Nerve Palsy
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.
Cranial Nerve 3 Palsy Differential
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.
CN3 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.
6th Nerve Palsy
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).
CN6 Differential
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.
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.
Fourth Cranial Nerve
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.
4th Palsy
When the fourth nerve is damaged, the eye has a tendency to shoot upwards when looking nasally. This is called a “nasal upshoot.”
CN4 Differential
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.
Aberrant Regeneration of 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.
Aberrant Regeneration Tumor
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 Down and Out
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.
Sixth Nerve Inwards
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 Palsy
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
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
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.
Subjective Maddox Rod
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.
Normal Maddox Rod
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.
Abnormal Maddox Rod
If the red line is described as being located “below the light” … this means the right eye is deviating upwards.
Fourth Nerve Trauma
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.
Vertical Fusion Amplitude
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.


Dr. Timothy Root is a practicing ophthalmologist and cataract surgeon in Daytona Beach, Florida. His books, video lectures, and training resources can be found at:


  1. Preciously well delivered! Thanks so very much sir! Pls kindly consider doing a video on HOW TO USE THE BINOCULAR INDIRECT OPHTHALMOSCOPE! This is one area that you have NOT touched on in terms of instrumentation usage. Pls sir counting on you so very much as we enjoy all your educative videos. God bless you sir and thanks once again for sharing your knowledge!!!!

  2. The video being a mix of opthalmo-knowledge and super powers, is awesome way of learning, keep it up sir, its very unique ways of learning difficult things so easily

  3. Saw this lecture LIVE in Daytona and it was wonderful – best and most concise explanation I’ve heard for these 3 motility disorders.

  4. This so amazing. I love the effort you put in to simplifying the eye. I was just searching for a good web to understand the eye muscles and I get your email.

    This is well explained and has definetly opened the pandoras box on palsies and cranial nerves.

    you rock Dr Tim

  5. Absolutely superb. So easy to understand. It is a pity I could not have seen a lecture like this when I was a student some 50 years ago.
    It is a must for any college student.

  6. Thank you very much Dr. Root,
    This video is the most interesting the way to learn the nerves and palsies.
    I always had struggle to learn and memorize them BUT with this video like every thing were engraved into my brain and will remember them always.

    Thank you very much.

  7. …Well,I can not find the right words for that kind of education. It is great ; it is fun ; it is effective and for me it will be more and more a “addiction” – again – THANK YOU !!

  8. Dear Dr.Timm thank you very much for your effort to make ophthalmology better and easier, I wish that someday I will be like You, again thanks .

  9. Great video! Wonderful lecture! I have been in private practice for 18 years and found this video to be entertaining revision of important clinical entities.
    Clive Novis
    Ophthalmologist, South Africa.

  10. merci
    thank you
    your videos are very helpfull for me at my work
    as an optician i am often the one that see s the customers for appointments
    and many times we need to know if we have and ermegency in front of us
    to have the patient seen more quikly
    Sight can be dammaged so fast that timming is important

    question when dammage has occured the option of working with prismes may be a possibility to use on a portion of the retina that is not dammaged
    by making glasses will you treat of that subject in the futur

    sorry for my english

    again thank you for the help you are spreading


  11. Dr.Root:
    Love your lectures and have even used one in my lecturing to Medical residents. I am an ophthalmologist. The most recent video “Super Eye Palsies” has a small error when you mention that the 3rd nerve innervates the Lateral Rectus. Thank you for all that you are doing and please don’t stop.
    Bob Morello

    Tim Root: Thanks Dr. Morello. I picked up on the typo before I uploaded the lecture. This is one of the difficulties with video lectures … it is hard to retract or “fix” these typos as I can’t simply delete that portion of the video. You’ll see that I inserted a “verbal typo” notice hovering over the animation at the moment I made the mistake. Thanks for commenting!

  12. Your videos has and continue to make me understand and retain immensely especially difficult and boring topics which are so important as this as mentioned can be life threatening ones. You have out done yourself ones more. So grateful, at the same time you are enjoying yourself too!

  13. Thanks for your wonderful works!I have followed this page for a long time. But English is not my mother language,so it is difficult to understand the audio.Could you provide some text materials?

  14. Not only you are a great teacher, you are also a great videographer! Looking forward to more of your great works.

  15. You are a very impressive and good teacher….would love to have more tutorial videos from you…yes, indirect ophthalmoscopy is another topic which I am awaiting….Thanks.

  16. With vertical deviations, is a Right Hyper the same as a Left Hypo during cover test? If so, how would you know which eye has the actual palsy?

  17. Pablo, you are correct … with small vertical deviations, it is hard to tell which eye has the problem. Using cover-uncover testing, however, you can sometimes tell which eye is deviated (because it is the one that moves to refixate). You may want to watch my tropia/phoria video to see examples of this.

    In real life, I’ll often just document what the right eye is doing vertically (hyper,hypo) on paper … and try to figure out the pattern later.

  18. with a trauma injury that is suspected of causing my fourth nerve palsy….does the double vision, etc happen right after the accident or can it get worse over time?

  19. excellent way to present such a hard topic for beginners ..thank you so much doctor.
    intern doctor hoping to be an Ophthalmologist
    Saudi Arabia

  20. Very hard subject. I think it´s difficult for everyone at the begining, specially the first 33 times (LOL)
    Very educational video. So far the easiest way to remember it I have found.

    Resident in ophthalmology

    Thank you


Please enter your comment!
Please enter your name here