Dr Ben Wild
Overview |
There are 12 cranial nerves that form the parasympathetic nervous system responsible for controlling the body. Interestingly, most of these nerves affect either the eyes or the eye muscles in some shape or form.
There are two 3rd nerves, otherwise known as oculomotor nerves. One controls some muscles around the right eye and the other controls the same muscles around the left eye. Muscles under control of the oculomotor nerve include the levator muscle that raises the top eyelids, the ciliary body muscles that control the ability to change focus, the iris sphincter muscle that shrinks your pupils, the superior, inferior and medial recti muscles responsible for moving the eyes up, down, and inwards, and the inferior oblique muscle responsible for pushing the eye upwards among other things.
A healthy pair of eyes looking off into the distance.
When the 3rd nerve stops working, called a 3rd nerve palsy, investigations must be done to determine the cause as some causes are life threatening. In some cases, a 3rd nerve palsy may present as a partial palsy (not showing all of the deficiencies in the actions listed above). It can present as just droopy eyelids, with just limited elevation of the eye, with just limited depression of the eye, or with or without enlarged pupils.
A right 3rd nerve palsy (eye on left shows a “down and out” appearance, an enlarged pupil, and a droopy eyelid.
Frontal view of a right eye with extraocular muscles. Highlighted muscles include the superior rectus, medial rectus, inferior rectus and inferior oblique muscles all of which are all controlled by the 3rd nerve.
Signs and Symptoms |
Signs
One eye is turned outwards and downwards, the pupil may or may not be enlarged, droopy eyelid, limited ability to move the eye up, down or inwards. Note: not all of these signs need to be present.
Symptoms
Vertical and horizontal double vision, loss of near vision.
Causes and Risk Factors |
Causes and Risk Factors
Without enlarged pupil: vascular diseases like diabetes and high blood pressure, aneurysms, meningiomas, granulomatous inflammation (auto-immune disease related), head trauma, brain tumors, giant cell arteritis.
With enlarged pupil: Same as without pupil involvement but more likely a compressive lesion post head trauma or brain aneurysm or brain tumor.
Prevention and Treatment |
Prevention
Ensure a healthy lifestyle to avoid vascular issues like high blood pressure, diabetes, etc.
Treatments
· Needs full neurological work up to identify the cause.
If the pupil is enlarged it necessitates a same day work up.
· Fresnel or permanent prism in glasses for the double vision.
· Patching one eye temporarily for the double vision.
· Botox.
· Surgery.
Prognosis |
If the 3rd nerve palsy is due to vascular diseases, this condition does tend to resolve on its own. If not, surgery for the droopy eyelid or double vision may be necessitated. When a 3rd nerve palsy is caused by a compressive lesion like a brain tumor or aneurysm, the nerve tends to regenerate but does so by creating new connections. These can range from the upper eyelid moving upwards when looking down, the pupil shrinking when looking towards the opposite eye, or the eye moving towards the opposite eye when trying to look upwards or downwards. These new connections become permanent even after treatment of the underlying issue.