What is a Third Nerve Palsy?
The third cranial nerve supplies innervation to the superior rectus muscle, inferior rectus muscle, medial rectus muscle, and inferior oblique muscle. These muscles are attached to the eye and control a majority of the movements of the eye. The third nerve also supplies innervation to the superior levator muscle which elevates the upper eyelid. The third nerve innervates a muscle in the iris of the eye that causes the pupil to constrict or become smaller when exposed to light or other stimuli.
A third nerve palsy is the complete or partial loss of innervation to the different muscles that it innervates.
What Causes a Third Nerve Palsy?
There are many possible causes of a third nerve palsy and they include:
CVA (cerebrovascular accident or stroke)
Aneurysm (most likely due to a aneurysm of the posterior communicating artery of the circle of Willis)
Cavernous sinus disease
Symptoms of a Third Nerve Palsy
The symptoms vary depending on the severity of the third nerve palsy and the degree of loss or decrease in innervation to each of the different ocular muscles.
Characteristic symptoms or sign is typically the eye turned down and out. There will be drooping of the upper eyelid to varying degrees. The pupil may or may not be dilated. The person may or may not have double vision depending on whether the upper lid is drooping enough to cover the pupil and block the vision. The eye position can also vary depending on which of the ocular muscles are affected and to what degree.
Treatment of Third Nerve Palsy
The treatment will depend on the etiology of the third nerve palsy. If the patient is having double vision, Fresnel prisms may be applied to the glasses to temporally relieve the double vision. The double vision may be relieved depending on the severity of the third nerve palsy. Patching of the eye may be necessary to relieve the double vision.
After six to twelve months, permanent prisms may be placed in glasses to control the double vision.
Eye muscle surgery may be necessary in some cases to try and relieve the double vision.