Extraocular motor nerve palsies
Dysfunctions of the third, fourth, and sixth cranial nerves are called extraocular motor nerve palsies. Each of these nerves innervates specific muscles.
The oculomotor (third cranial) nerve innervates the inferior, medial, and superior rectus muscles; the inferior oblique extraocular muscles; the pupilloconstrictor muscles; and the levator palpebrae muscles.
The trochlear (fourth cranial) nerve innervates the superior oblique muscles.
The abducens (sixth cranial) nerve innervates the lateral rectus muscles.
The superior oblique muscles control downward rotation, intorsion, and abduction of the eye. Complete dysfunction of the third cranial nerve is called total oculomotor ophthalmoplegia and may be associated with other central nervous system abnormalities. Myasthenia and dysthyroid disease should be examined as differential diagnoses.
The most common causes of extraocular motor nerve palsies are diabetic neuropathy and pressure from an aneurysm or brain tumor. Other causes of these disorders vary, depending on the cranial nerve involved.