Third Nerve Palsy: Complete, Partial & Pupil-Sparing

A clinically accurate animation of a right third nerve (oculomotor) palsy, comparing a complete pupil-involving palsy, a complete pupil-sparing palsy and a partial palsy. A 3D eye model shows which muscles stop working, with animations of how an aneurysm and small-vessel disease damage the nerve. What to look for: • Ptosis - the eyelid droops (levator palpebrae superioris) • The eye rests "down and out" - lateral rectus (CN VI) and superior oblique (CN IV) still work • Abduction preserved; elevation, depression and adduction affected • Intorsion on downgaze - the superior oblique, showing the trochlear nerve is intact • Pupil: dilated and unreactive to light (direct and consensual) in a pupil-involving palsy Why the pupil matters: • Complete palsy + dilated pupil: compressive until proven otherwise (e.g. posterior communicating artery aneurysm) - urgent vascular imaging • Complete palsy + normal pupil: commonly microvascular (diabetes, high blood pressure, smoking); also consider other systemic causes e.g. vasculitis. Rarely, a compressive lesion can spare the pupil • Partial palsy: a normal pupil does not rule out compression - urgent vascular imaging Chapters 0:00 The oculomotor nerve 0:13 Eye model: which muscles stop working 0:34 Variants 0:39 Complete palsy: ptosis and "down and out" 1:15 Eye movements 1:34 Intorsion 1:54 The pupil 2:28 Compressive causes 2:46 Pupil-sparing palsy 3:16 Partial palsy 4:02 Summary This video is for educational purposes only and is not medical advice. #Neurology #ThirdNervePalsy #OculomotorNerve #CranialNerves #NeuroExam #Ophthalmology #MedicalEducation