Oculomotor nerve palsy

A complete oculomotor nerve palsy produces the following constellation of findings:

• Ptosis - paralysis of the levator palpebrae muscle and unopposed contraction of the orbicularis oculi muscle, which is innervated by the facial nerve (the lid space may be slightly open because of contraction of the frontalis muscle).

• Fixed position of the eye - looking downward and outward, caused by unopposed contraction of the lateral rectus and superior oblique muscles (innervated by CN VI and IV, respectively).

• Dilation of the pupil - caused by loss of contraction of the sphincter pupillae muscle, innervated by the parasympathetic portion of the oculomotor nerve; the pupillary light and accommodation reflexes are absent.