Mydriasis of Third Nerve Palsy

    • Dilated (mydriatic) pupil as part of third nerve palsy
    • Attributed to damage of the parasympathetic component of the third nerve
    • Common causes: head trauma, cerebral hemispheric herniation, ischemia, inflammation, aneurysm
    • Core clinical features
      • Patient reports diplopia
      • Mydriasis may be marked or minimal and does not cause symptoms
      • Mydriatic pupil constricts less forcefully to direct light than does the unaffected pupil
      • Ptosis on the side of the mydriatic pupil
      • Ocular ductional deficits in the domain of the third nerve on the side of the mydriatic pupil
    • Traumatic, inflammatory, dysplastic iridoplegia
    • Pharmacologic mydriasis
    • Tonic (Adie) pupil
    • In adults, order prompt CT/CTA; in children, order prompt MRI/MRA
    • If CT/CTA or MRI/MRA is negative, order brain MRI only if ischemia is not a likely cause in adults
    • If brain MRI is negative, proceed with LP in the appropriate setting
    • Tip: third nerve palsy never causes mydriasis without also causing ptosis or ocular ductional deficits
    • Depends on the underlying condition
    • Trap: delayed diagnosis of third nerve palsy caused by brain aneurysm could lead to aneurysmal rupture with marked morbidity and 50% mortality

    Pupil Disorders

    Anisocoria Overview Physiologic Anisocoria Horner Syndrome Tonic (Adie) Pupil Argyll Robertson Pupil Pharmacologic Mydriasis Episodic Mydriasis Iridoplegic Mydriasis Mydriasis of Third Nerve Palsy Tectal Pupils