Introduction Muscles of the EyeMuscleInnervationMajor FunctionSuperior rectusOculomotor nerve (CN III)Elevation and intorsionInferior rectusOculomotor nerve (CN III)Depression and extorsionLateral rectusAbducens nerve (CN VI)Abductionlateral movement of the eyeMedial rectusOculomotor nerve (CN III)Adductionmedial movement of the eyeSuperior obliqueTrochlear nerve (CN IV)Depression and intorsionInferior obliqueOculomotor nerve (CN III)Elevation and extorsion Cranial Nerve Palsies Oculomotor nerve palsy (3rd nerve palsy) results in paralysis of the innervated extraocular muscles therefore, the lateral rectus and superior oblique muscles are preserved leads to a "down and out" position of the eye at rest with additional findings depending on the location and cause of the lesion other findings that can be seen with a third nerve palsy include ptosis due to the oculomotor nerve's innervation to the levator palpebrae muscle mydriasis due to the parasympathetic fibers of the oculomotor nerve innervating the iris sphincter muscles etiologies compression causes aneurysms (e.g., posterior communicating artery aneurysm) uncal herniation pathogenesis first compresses the outer components of the 3rd nerve (where the parasympathetic fibers are) presentation painful "down and out" eye with a "blown pupil" (mydriasis) vascular disease causes diabetes hypertension hyperlipidemia pathogenesis ischemic damage to the interior components of the nerve presentation painless "down and out" eye with sparing of the pupil Trochlear nerve palsy (4th nerve palsy) results in paralysis of the superior oblique muscle, which normally intorts and depresses the eye results in hypertropia (eye elevation) and extorsion of the eye etiologies head trauma the trochlear nerve is thin and has a long course from the brainstem to the eye, putting it at an increased risk for shear injury during head trauma presentation head tilting away from the affected eye corrects the extorsion chin tucking and slightly looking upward corrects the hypertropia Abducens nerve palsy (sixth nerve palsy) results in paralysis of the lateral rectus muscle, which normally abducts the eye etiologies increased intracranial pressure (e.g., intracranial tumors, pseudotumor cerebri, and hydrocephalus) the abducens nerve has a long course over the clivus and petrous bone therefore, it is susceptible to experiencing downward traction in the setting of space-occupying lesions presentation horizontal diplopia