Adie's tonic pupil presenting with unilateral photophobia successfully treated with dilute pilocarpine

A 40-year-old healthy man presented with a 4-month history of photophobia, blurred vision and a right dilated pupil. Examination revealed a right pupil that was not reactive to light but constricted strongly to a near target and slowly redilated when he looked back in the distance. Pharmacological testing with dilute pilocarpine 0.1% resulted in constriction of the right pupil but no change in the left pupil. This also resulted in resolution of his photophobia and blurry vision. Neurological examination was otherwise normal, and a diagnosis of Adie's tonic pupil was made. The main differential diagnosis to consider for a large pupil is a third nerve palsy, pharmacological mydriasis, tonic pupil and local iris processes, such as iris sphincter tears from trauma. Knowledge of the key features of these conditions can avoid wasted resources from unnecessary testing. Dilute pilocarpine 0.1% three times a day can be considered as a pharmacological therapy for symptomatic relief.