The brainstem connects the spinal cord to the brain. The brainstem performs spinal-cord like functions for the head. The cranial nerves emanate from the brainstem. They provide sensory and motor functions that deal with the special senses (smell, sight, hearing, equilibrium, and taste).
The second cranial nerve is called the optic nerve. It sends visual information from the eye to the brain. The third cranial nerve is called the oculomotor nerve. It is involved with eye movement, eyelid movement, and the function of the pupil and lens. The fourth cranial nerve is called the trochlear nerve and the sixth cranial nerve is called the abducens nerve. They each innervate an eye muscle involved in eye movement. The fifth cranial nerve is called the trigeminal nerve. It provides facial sensation (including corneal sensation).
A palsy is a lack of function of a nerve. A cranial nerve palsy may cause a complete or partial weakness or paralysis of the areas served by the affected nerve. In the case of a cranial nerve that has multiple functions (such as the oculomotor nerve), it is possible for a palsy to affect all of the various functions or only some of the functions of that nerve.
A cranial nerve palsy can be congenital, traumatic, or due to vascular disease (hypertension, diabetes, strokes, aneurysms, etc). They can also be due to infections, migraines, tumors, or elevated intracranial pressure. The age of the patient, as well as clinical findings, will help point the physician toward the correct diagnostic tests needed to determine the etiology.
3rd, 4th, and 6th nerve palsies can limit eye movements and produce diplopia (double vision). The positioning of the two images will be different based on which cranial nerve is affected. In addition to limited eye movements, a 3rd nerve palsy can also cause ptosis (droopy eyelid) or mydriasis (an abnormally dilated pupil).
Please refer to the specific FAQ sections on 3rd, 4th, and 6th nerve palsies for specific information and recommendations (located on this website). In general, some cases may resolve spontaneously. In other cases, diplopia may be relieved with prism glasses, occlusion therapy, botulinum toxin, or surgery. The best treatment will be determined by the ophthalmologist after a thorough evaluation.
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