CN III Palsy

A cranial nerve III palsy affects the third cranial nerve, which controls most of the eye's movements, eyelid lifting, and pupil constriction. This condition can cause double vision, drooping of the eyelid (ptosis), and difficulty moving the eye in certain directions. It involves the nervous system, specifically the nerves that control eye muscles. The affected eye may appear to be looking downward and outward due to unopposed action of other eye muscles. Additionally, the pupil may be abnormally large or unresponsive to light. These symptoms can significantly impact vision and daily activities.

CN III palsy is a neurological disorder characterized by dysfunction of the oculomotor nerve, which innervates the majority of the extraocular muscles, the levator palpebrae superioris, and the sphincter pupillae. The core pathology involves impaired nerve conduction due to ischemia, compression, trauma, or inflammation. Common causes include microvascular ischemia (often related to diabetes or hypertension), aneurysmal compression (especially from a posterior communicating artery aneurysm), and traumatic injury. Clinically, it presents with ptosis, ophthalmoplegia (limited eye movements), and pupil abnormalities such as dilation or unreactivity. The presence or absence of pupil involvement helps differentiate between ischemic and compressive etiologies. This condition is significant because it can indicate life-threatening causes like aneurysm rupture or brainstem pathology.