Diagnosis is radiological with computed tomogram (CT) or magnetic resonance imaging (MRI). Patients usually experience pain with this entity. The most well-known, life-threatening cause of TNP is a posterior communicating artery aneurysm causing pressure on the third nerve. Isolated pupillary dilation is not classically considered a third nerve palsy however, careful evaluation for subtle ptosis or abnormal extraocular movement is necessary to eliminate a TNP using this criterion. Important etiologies of anisocoria include third nerve palsy, Adie pupil, pharmacologic mydriasis, pharmacologic miosis, traumatic mydriasis, physiologic anisocoria, and Horner syndrome.Ī third nerve palsy (TNP) may spare the pupil or cause it to dilate with no reaction to light or convergence.
