The third cranial nerve, which is also called the oculomotor nerve, has many roles in controlling the eyes. If something happens and damages this cranial nerve, there are several classic signs and symptoms that present. A cranial nerve three palsy occurs when the damage to the nerve is so severe that it no longer provides any innervation to the tissue.
What are Cranial Nerves?
There are twelve cranial nerves which are major nerves in the head and neck. These twelve nerves arise from the brain stem and are responsible for many major functions throughout the body.
The cranial nerves are named and numbered with each having a written name based on the function of the structures that the nerve innervates and being numbered based on how high in the brainstem the nerve originates.
The cranial nerves which directly impact the eyes are cranial nerves 2, 3, 4, 5, 6, and 7.
Most of the cranial nerves take a path through the brain to the front of the head, including the eyes.
What Does the Oculomotor Nerve Do?
The third cranial nerve, the oculomotor nerve, has several major functions related to the eyes. As the name of the nerve suggests, the oculomotor nerve is responsible for many eye movements including moving the eye up, down, and in towards the nose.
The oculomotor nerve also provides motor innervation to the muscle that raises the eyelid when opening the eye normally without eyebrow movement.
An involuntary function of cranial nerve three is the constriction of the pupil when light enters the eyes.
What are the Signs and Symptoms of a Cranial Nerve 3 Palsy?
If there is a complete palsy or paresis of cranial nerve three, the three main signs that will be observed.
The first and most apparent sign will be that the eyelid on the side of the cranial nerve palsy is closed and cannot be opened.
If the eyelid is completely closed, it must be manually lifted to observe the eye as there is no innervation to the muscle needed to lift the eyelid.
Another sign of a cranial nerve three palsy is that the eye of the affected side will appear to be deviated slightly outward and downward.
The eye muscles which move the eye out and down are the only muscles that are still receiving innervation and have function so the eye will be directed in that direction.
If the cranial nerve three palsy is truly a complete palsy, the third sign that will be seen is that the pupil of the affected eye will be large and nonresponsive to light.
The pupil will appear much larger than the other eye’s pupil.
What is the Prognosis for a Cranial Nerve 3 Palsy?
Depending on the cause and severity of the cranial nerve three palsy, the prognosis may vary.
In the best cases, most of the function to the nerve can return if the palsy is due to a lack of blood flow to the nerve and the blood flow is restored.
In the most severe cases, there can be little to no recovery of function. These cases are more likely due to permanent damage such as trauma or surgical severing of the nerve.