Do unequal pupils always indicate significant pathology?

Author: Eugene Lloyd / Editor: Jason Kendall / Reviewer: Jolene Rosario, Philip Delbridge / Codes: NeuP2, OptC2, SLO1, SLO2 / Published: 10/12/2020 / Reviewed: 01/11/2024

A 31-year-old female presented to the Emergency Department (ED) complaining of a dilated left pupil that had been noticed by a colleague at work. There was no history of ocular trauma or use of mydriatic drugs. The patient had experienced intermittent right occipital headaches for the previous week that were reduced in severity by paracetamol. The patient had experienced migraines during her teenage years but was otherwise well. She did not use any regular medication, was a non-smoker, consumed approximately three units of alcohol per week and denied using illicit drugs.

On examination she was apyrexial, appeared well and there were no signs of meningeal irritation. The left pupil had a diameter of 8mm and the right 3mm. The left pupil did not demonstrate a direct nor consensual reflex but exhibited a weak response to convergence. The visual acuity was 6/6 for both eyes and there were no visual field defects. The function of the extraocular muscles was normal and the patient did not exhibit ptosis. The rest of the neurological examination was normal.